Microbiology: Module 10 - Host Defenses and Innate Immunities + Adaptive Specific Immunity and Immunization

Benefits and Treatment of Fever

- Inhibits multiplication of temperature-sensitive microorganisms i.e. poliovirus, cold viruses, herpes zoster virus, systemic and SQ fungal pathogens, Mycobacterium species, syphilis spirochete - Impedes nutrition of bacteria by reducing the available iron = retards several enzymatic reactions needed for pathogen growth - Increases metabolism - Stimulates immune reactions and protective physiological processes - speeds up hematopoiesis, phagocytosis, and specific immune reactions - Stimulates the activities of T cells and increase the effectiveness of interferon

Characteristics of Immunoglobulin (Ig) Classes**

IgG - Monomer # of antigen binding sites: 2 MW: 150,000 % of total antibody in serum: 80% Average life in serum (days): 23 Crosses placenta: Yes Fixes complement: Yes Binds to: Phagocytes Biological Function: Long-term immunity; memory antibodies; neutralizes toxins; viruses IgA - Dimer, Monomer # of antigen binding sites: 2 or 4 MW: 170,000-385,000 % of total antibody in serum: 13% Average life in serum (days): 6 Crosses placenta: No Fixes complement: No Binds to: Epithelial cells Biological Function: Secretory antibody; on mucous membranes IgM - Pentamer # of antigen binding sites: 10 MW: 900,000 % of total antibody in serum: 6% Average life in serum (days): 5 Crosses placenta: No Fixes complement: Yes Binds to: NA Biological Function: Produced at first response to antigen; can serve as B-cell receptor IgD - Monomer # of antigen binding sites: 2 MW: 180,000 % of total antibody in serum: 0.001% Average life in serum (days): 3 Crosses placenta: No Fixes complement: No Binds to: NA Biological Function: Receptor on B cells for antigen recognition IgE - Monomer # of antigen binding sites: 2 MW: 200,000 % of total antibody in serum: 0.002% Average life in serum (days): 2.5 Crosses placenta: No Fixes complement: No Binds to: Mast cells and basophils Biological Function: Antibody of allergy; worm infections

T-Cell Responses and Cell-Mediated Immunity

• Cell-mediated immunity (CMI)* - requires the direct involvement of T lymphocytes in the immune response - Response of T cells • T cells secrete cytokines that act directly on other cells • Before T cells get activated, the antigen must be presented in association with an MHC complex on a APC, to ensure recognition of self • Once activated, the T cell transforms in preparation for mitotic divisions to become a subset of effector and memory cells • Differentiation will be determined by APC interleukin secretion • T cell responses involve a direct interaction with other cells, rather than the secretion of molecules into circulation like that seen in humoral immunity carried out by B cells**

T-Cell Activation

1. APCs (here a dendritic cell) are found in large numbers in lymphatic tissues, where they frequently encounter complex antigens such as microbes. APCs engulf the microbes, take them into intracellular vesicles, and degrade them into smaller, simpler peptides. 2. The antigen peptides complexed with MHC-II receptors are transported to the APC membrane (inset A). From this surface, location the antigens are readily presented to a T helper cell, which is specific for the antigen being presented. 3. The APC and T helper cell cooperate in the formation of a receptor complex that triggers T-cell activation (inset B). - First, the MHC-II antigen on the APC binds to the T-cell receptor. - Next, a coreceptor on the T cell (CD4) hooks itself to a position on the MHC-II receptor. This combination ensures the simultaneous recognition of the antigen (nonself) and the MHC receptor (self). - These stimuli provide a signal that is relayed to the T-cell genetic material, thus activating the T helper cell. - The activated T cell is stimulated to release interleukins and to assist other lymphocytes in their functions.

Main Events in B-cell Responses

1. Clonal selection and binding of antigen - precommitted B cell of a particular clonal specificity picks up the antigen on its Ig receptors and processes it into small peptide determinants - Antigen is then bound to the MHC-II receptors on the B cell - MHC/Ag complex on the B cell is bound by T-cell receptors 2. Induction by chemical mediators - B cell receives developmental signals from macrophages and T cells (interleukin-2 and interleukin-6) and other growth factors (IL-4, IL-5) 3. Combination of these stimuli on the membrane receptors causes a signal to be transmitted internally to the B-cell nucleus 4. Events trigger B-cell activation - activated B cell (Lymphoblast) enlarges and increases its synthesis of DNA and protein in preparation for entering the cell cycle and mitosis 5-6. Clonal expansion - stimulated B cell multiples through successive mitotic divisions and produces large population of genetically identical daughter cells - Memory Cells - cells that stop short of becoming fully differentiated - remain for long periods to react with that same antigen later - Expands clone size - exposure to that antigen provides more cells with that specificity - Expansion of clone size = increased memory response - Plasma cells - progeny of activated B cell that actively produces and secretes antibodies against specific microbe 7. Antibody production and secretion - primary action of plasma cells is to secrete copious amounts of antibodies with the same specificity of original receptor into the surrounding tissues - Individual plasma cell can produce around 2000 antibodies per second - production does not continue indefinitely - Plasma cells do not survive for long, deteriorate after synthesizing antibodies

Examples of Origins of Immunity

1. Natural Active immunity: Getting an infection - After recovering from infectious disease, a person may be actively resistant to reinfection (period varies according to the disease 2. Natural Passive Immunity: Mother to Child - IgG antibodies bodies from the maternal bloodstream can pass or be actively transported across the placenta to the fetus - IgA antibodies from mother's milk react against microbes entering the intestine - Immunity to the fetus occurs when the transfer of maternal tetanus antibody (mainly lgG) across the placenta is provided* 3. Artificial Active Immunization: Vaccination - Microbial (antigenic) stimulus, which triggers the immune system to produce antibodies and memory cells 4. Artificial Passive Immunization: Immunotherapy - A patient at risk for acquiring a particular infection is administered a preparation that contains specific antibodies against that infectious agent - Pooled human serum from donor blood (gamma globulin) and immune serum globulins containing high quantities of antibodies are the usual sources - Immune serum globulins are used to protect people who have been exposed to certain diseases i.e. Hepatitis A, rabies, tetanus - Used prophylactically in case of immunodeficiency diseases* • Artificial Immunization - any clinical process that produces immunity to a subject; often used to give advance protection against infection = Immunoprophylaxis • Term vaccination originated from vacca (cow) - cowpox virus was used in the 1st prep for active immunization against smallpox

Which of the following are associated with adaptive or acquired immunity?

1. Specificity 2. Memory 3. recognition of antigens

Development of the Immune Response System

• Cell receptors or markers confer specificity and identity of a cell • Major functions of RECEPTORS are**: - To perceive and attach to non-self or foreign molecules - To promote the recognition of self antigens - To receive and transmit chemical messages among other cells of the system - To aid in cellular development

Characteristics of Leukocytes

Cell Type - Prevalence in Circulation - Primary Function - Features - Appearance: Neutrophils - 55%-90% of white blood cells - General phagocytosis - Life span of 2 days, with only 4-10 hours spent in the circulation - Multilobed nuclei; small purple granules containing digestive enzymes Eosinophils - 1%-3% of white blood cells - Destruction of parasitic worms; mediators of allergy - Found in much higher numbers in the spleen and bone marrow - Bilobed nucleus with large orange granules containing toxic proteins, inflammatory mediators, and digestive enzymes Basophils - 0.5% of white blood cells - Active in allergy, inflammation, parasitic infections - Cytoplasmic granules contain histamines, prostaglandins, and other chemical mediators of the allergic response - Pale-staining, constricted nuclei with dark blue to black granules Monocytes - 3%-7% of white blood cells - Phagocytosis, followed by final differentiation into macrophages and dendritic cells - Monocytes also secrete several chemicals that moderate the functions of the immune system - Largest WBC; nuclei large, ovoid, and often indented-no cytoplasmic granules visible using a light microscope Lymphocytes - 20%-35% of white blood cells - Specific (acquired) immunity - Two types of lymphocytes exist., T cells are responsible for cell-mediated immunity, whereas B cells are responsible for humoral immunity - Small spherical cells with uniformly staining dark, round nuclei

Selected Monoclonal-Antibody Based Drugs

Drug Names Chemical (Trade) - Used in Therapy for: Cancer Drugs - • Trastuzumab (Herceptin) - Breast cancer • Rituximab (Rituxa) - B-cell disorders (lymphomas, leukemias) • Alemtuzumab (Campath) - Chronic T-cell leukemia and lymphoma • Pembrolizumab (Keytruda) - Metastatic melanoma and lung cancer Other Applications - • Omalizumab (Xolair) - Asthma • Vedolizumab (Entyvio) - Ulcerative colitis • Infliximab(Remicade) - Crohn's disease • Palivizumab(Synagis) - Respiratory syncytial virus (RSV) • Adalimumab (Humira) - Rheumatoid arthritis, psoriasis

Overview of Host Defense Mechanisms

Line of Defense - Innate/Acquired - Specific or Nonspecific - Development of Immunologic Memory - Examples: ▪ First - Innate - Nonspecific - No - Physical barriers: skin, tears, coughing, sneezing; Chemical barriers: low pH, lysozyme, digestive enzymes; Genetic barriers: resistance inherent in genetic makeup of host (pathogen cannot invade) ▪ Second - Innate - Mostly nonspecific - No - Phagocytosis, inflammation, fever, interferon, complement ▪ Third - Acquired - Specific - Yes - T lymphocytes, B lymphocytes, antibodies

sequence for the processing of antigens originated outside of the cell after their ingestion by phagocytes:

Proteins are broken into fragments within a vesicle - which fuses with a Golgi vesicle containing Class II MHCs - and this complex is transported to the plasma membrane

B Cells versus T Cells

T CELLS Site of Maturation: Thymus gland Immune surface Markers: T- cell receptor, CD molecules, MHC I receptors Circulation in Blood: High numbers Receptors for Antigen: T-cell receptor (TCR) Distribution in Lymphatic Organs: Paracortical sites (interior to the follicles) Require Antigen Presented with MHC: Yes Product Antigenic Stimulation: Helper and cytotoxic T cells and memory cells General Functions: Regulate immune functions, kill foreign and infected cells, synthesize cytokines B CELLS Site of Maturation: Bone marrow Immune surface Markers: Immunoglobulin MHC I and MHC II receptors Circulation in Blood: Low numbers Receptors for Antigen: Immunoglobulins D and M Distribution in Lymphatic Organs: Cortex (in follicles) Require Antigen Presented with MHC: No Product Antigenic Stimulation: Plasma cells and memory cells General Functions: Produce antibodies to target, inactivate, and neutralize, antigens*

complex structure of the bacterial cell surface in regard to immunity

They have many different epitopes, which each bind to specific antibodies.

Types of T Cells

Types - Primary Receptors on T Cell - Functions/Important Features: • T helper cell 1 (TH1) - CD4 - Activates other CD4 and CD8 cells; secretes IL-2, tumor necrosis factor, and interferon gamma; responsible for delayed hypersensitivity; interacts with MHC-II receptors • T helper cell 2 (TH2) - CD4 - Drives B-cell proliferation; secretes IL-4, IL-5, IL-6, IL-10; can dampen TH1activity • T helper 17 - CD4 - Promotes inflammation; secretes IL-17 • T regulatory cell (Treg) - CD4, CD25 - Involved in development of immune tolerance; suppression of pathological immune responses, inflammation, autoimmunity • T cytotoxic cell (TC) - CD8 - Destroys a target foreign cell by lysis**; important in destruction of cancer cells, virus-infected cells; graft rejection; requires MHC I for function May have some regulatory functions.

Lymphatic Circulation

a) The finest level of lymphatic circulation begins with blind capillaries (green) that pick up foreign matter from the surrounding tissues and transport it in lymph away from transport it in lymph away from transport it in lymph away from the extremities via a system of small ducts. b) The ducts carry lymph into a circuit of larger ducts that ultimately flow into clusters of filtering organs, the lymph nodes. c) A section through a lymph node reveals the afferent ducts draining lymph into sinuses that house several types of white blood cells. Here, foreign materials is filtered out and processed by lymphocytes, macrophages, and dendritic cells. d)and (e) Lymph continues to trickle from the lymph nodes via efferent ducts into a system of larger drainage vessels, which ultimately connect with large veins near the heart. In this way, cells and products of immunity continually enter the regular circulation.

Antivenin, given to people who have been bitten by rattlesnakes, consists of antibodies that bind to and inactivate the snake's venom. Antivenin is produced by injecting sheep with rattlesnake venom (which causes the sheep to produce antibodies) and then collecting the antibodies from the blood of the sheep, for later injection into humans. In this case, the sheep develops__________ immunity while the human experiences __________ immunity.

artificial active artificial passive

Stages in the Complement Cascade

b) Cascade and Amplification. C5 factor is acted on by C3b, which converts it to C5b. C5b becomes bound to the membrane and serves as the starting molecule for the chain of events that assemble the complex in (c) and (d). c) Polymerization. C5b is a reactive site for the final assembly of an attack complex. In series, C6, C7, and C8 aggregate with C5b and become integrated into the membrane. They form a substrate upon which the final component, C9, can bind. Up to 15 of these C9 units ring the central core of the final membrane attack complex (MAC). d) Membrane Attack. Insertion of MACs produces hundreds of tiny holes in the cell membrane. This can cause lysis and death of eukaryotic cells and many gram-negative bacteria. - Two products of the cascade reaction — C3a and C5a — have additional inflammatory functions. Both molecules stimulate mast cell degranulation, enhance chemotaxis of white blood cells, and act as inflammatory mediators.

Artificial Passive Immunization

• 1st attempts involved transfusion of horse serum containing antitoxins to prevent tetanus and to treat patients exposed to diphertheria • Useful for immunocompromised patients who cannot be vaccinated. Acts immediately; protection lasts 2-3 months ▪ Human antisera • Immune serum globulin (ISG)* - called gamma globin, contains immunoglobin extracted from the pooled blood of at least 1000 human donors * - Method of processing ISG concentrates the antibodies to increase potency and eliminates potential pathogens i.e. Hep B and HIV - Treatment of choice in preventing measles and hepatitis A and in replacing antibodies in immunodeficient patients • Specific immune globulin (SIG) - from donors in a hyperimmune state after being vaccinated or infected by pertussis, tetanus, chickenpox, and hepatitis B ▪ Antisera and antitoxins of animal origin • Antisera and antitoxins of animal origin - Sera produced in horses are available for diphtheria, botulism, and spider and snake bites

Classes of Immunoglobulins

• 5 functional classes (isotopes) of immunoglobulins (Ig): - IgG - monomer, produced by plasma cells (primary response) and memory cells (secondary), most prevalent - IgA - monomer circulates in blood, dimer in mucous and serous secretions - IgM - five monomers, first class synthesized following Ag encounter - IgD - monomer, serves as a receptor for antigen on B cells - IgE - Involved in allergic responses and parasitic worm infections • The differences in these classes are due primarily to variations in the Fc

Necrotizing Fasciitis

• A condition in which a wound does not respond to antibiotic treatment and the surrounding tissue becomes damaged and dies.

1st Line of Defense: Barriers at the Portal of Entry

• A number of defenses are a normal part of the body's anatomy and physiology • These are inborn (innate), nonspecific defenses can be divided into three categories: 1. Physical or anatomical barriers at the body surface 2. Chemical defenses 3. Genetic resistance to infection • They block the entry of not only microbes but any foreign agent (living or not)

Immunity Categories by Mode of Acquisition: ACTIVE IMMUNITY PASSIVE IMMUNITY NATURAL IMMUNITY ARTICIFIAL IMMUNITY

• Active Immunity - The result of the body's response to exposure to antigen** - occurs when an individual receives an immune stimulus (microbe) that activates specific lymphocytes causing an immune response i.e. production of antibodies - Can be stimulated by natural or artificial means - Several characteristics: 1. Essential attribute of an immunocompetent individual 2. Creates a memory that renders the person ready for quick action upon re-exposure to that same microbe 3. Requires several days to develop * 4. Can last for a relatively long time* • Passive Immunity - occurs when an individual receives immune substances (primarily antibodies) that were produced actively by the immune system of another human or animal donor - Recipients are protected for a time even though they have not had actual exposure to the microbe - Can be stimulated by natural or artificial means - Ultimately body disposes of them - Characteristics: 1. Lack of memory for the original antigen 2. No production of new antibodies against that disease 3. Immediate onset of protection 4. Short-term effectiveness because antibodies have limited period of function - Ultimately body disposes of them • Natural Immunity - encompasses immunity that is acquired during any normal biological experiences of an individual but not through medical intervention Ex) Occurs when you get chickenpox from contact with an infected person. • Artificial Immunity - protection from infection obtained through medical procedures; type of immunity induced by immunization with vaccines and immune serum

Macrophages

• After emigrating out of the bloodstream into tissues, monocytes turn into Macrophages by inflammatory mediators • Process marked by increase in size and development of lysosomes and other organelles • Retain capacity to move about • Macrophage and dendritic cells can remain nomadic or take up residence in a specific organ depending on stage of development and immune stimuli received • Scavenge and process foreign substances to prepare them for reactions with B and T lymphocytes • Specialized macrophages - Histiocytes* - migrate to a certain tissue and remain there Ex) Alveolar (lung) macrophages, Kupffer cells (liver), Langerhans cells (skin), and macrophages in spleen, lymph nodes, bone marrow, kidney, bone, brain • Dendritic cells - another product of the monocyte line - constructed in skin and linings of mucous membranes - Process foreign substances and prepare them for reactions w/ selected lymphocytes

Functional Categories of ANTIGENS**

• Alloantigens - cell surface markers and molecules that occur in some members of the same species but not in others - Determine blood group and major histocompatibility profile - Responsible for incompatibilities in blood transfusion or organ grafting • Superantigens - bacterial proteins that are potent T cell stimulators - Toxic shock toxin (massive release of cytokines leading to cell death) and enterotoxin of Staphlyococcus • Allergens - antigens that evoke allergic reactions • Autoantigens - molecules that escaped lymphocyte differentiation during which immune tolerance to self tissue developed; molecules on self tissues for which tolerance is inadequate Ex) Autoimmune diseases i.e RA

Development of Immunoglobulins

• An undifferentiated lymphocyte has: - ~150 genes that code for the variable region of light chains - ~250 genes for the variable(V) and diversity (D) regions of the heavy chains - Only a small number of genes code for the constant (C) regions and the joining (J) regions that link segments of the final molecule • After development only the selected V and D gene segments are active in the mature cell, and all the other V and D genes have been deleted - This maintains the lymphocytes specificity • Once synthesized, immunoglobulin is transported to cell membrane and inserted there to act as a receptor 1) The heavy-chain genes are composed of four separate segments (V, D, J, and C) that are 2) transcribed and translated to form the heavy polypeptide chains. 3) The light-chain genes are put together like heavy ones, except that the final gene is spliced from three gene groups (V, J, and C), making smaller polypeptides. 4) During final assembly, first the heavy and light chains are bound, and then the heavy-light combinations are connected to form the immunoglobulin molecule.

Monoclonal Antibodies

• Antibodies used as tools for locating or identifying antigens • Polyclonal Antibodies - mixture of different antibodies because it reflects dozens of immune reactions from a wide variety of B-cell clones • Even single species of microbe has many epitopes and will induce expression of antibodies with different specificities • Antibodies produced from a single B-cell clone that recognize a single antigen are called Monoclonal Antibodies* (MABs) - used to target specific cells in the body that may differ only slightly from other cells i.e. cancerous lung cells from healthy lung cells

Characteristics of Antigens and Immunogens

• Antigen (Ag) - substance that elicits immune response in specific lymphocytes - Antigenicity - property of behaving as an antigen - Must meet criteria to be antigenic: Foreignness, size, shape, and accessibility • Immunogen / Immunogenicity - type of antigen that does induce a specific immune response when introduced into the body; not all antigens fit the conditions to stimulate an immune response Ex) small polysaccharides from the capsule of the bacterium Haemophilus influenzae (cause of meningitis) - Molecules are foreign and antigenic but are too small to trigger a lymphocyte response = antigenic but not immunogenic - Must be altered to produce a vaccine so the immune system can recognize and react to it • Important characteristic of antigen: immune cells react to it as non-self or as foreign = it is not a "normal" constituent of the body • Most materials that serve as antigens fall into these chemical categories: - Proteins and large polypeptides (enzymes, cell surface receptors, hormones, exotoxins) - Molecules that contain 2 or more different macromolecules bound together Ex) lipoproteins and lipopolysaccharides - originate from the cell membranes or cell walls of microbes; nucleoproteins - unbound DNA is too regular and repetitive in structure to be antigenic; polysaccharides (bacterial capsules) and glycolipids (mycolic acid of M. TB)

Phases of a Specific Immune Response

• Antigen-Independent Development - lymphocytes arise from the same stem cells but differentiate into two distinct cell types • Antigen Contact - foreign cells bear molecules that are recognized by B cells or engulfed by dendritic cells or macrophages • Humoral Immunity - involves production of antibodies by plasma cells • Cell-Mediated Immunity - involves helper T cells and cytotoxic T cells • Antigen Presentation - required for activation of T cells

Events in B-Cell Responses

• B-cell activation and antibody production - Once B cells process the Ag, interact with THcells, and are stimulated by growth and differentiation factors, they enter the cell cycle in preparation for mitosis and clonal expansion - Divisions give rise to plasma cells that secrete antibodies and memory cells that can react to the same antigen later

Lymphatic System

• Begins in tissues as tiny capillaries that transport a special fluid (lymph) through an increasingly larger system of vessels and filters (lymph nodes) • Connects to major vessels that drain back into the regular circulatory system • Major Functions of Lymphatic or Lymphoid System related to Immune Defense**: 1. Provide an additional route for the return of extracellular fluid to the circulatory system 2. Help drain fluid that has accumulated due to the inflammatory response; carries away excess fluid from inflamed tissue 3. Render surveillance, recognition, and protection against foreign materials through a system of lymphocytes, phagocytes, and antibodies • Main function of lymphatic system is returning lymph to the circulation, lymph flows only in one direction, moving from the extremities toward the heart - eventually will be returned to the bloodstream through the thoracic duct and RT lymphatic duct near the base of the neck • Lymph travels through the vessels of the lymphatic system, only moved through the contraction of skeletal muscles that surround the lymphatic ducts • Dependence on muscle movement helps to explain the swelling of the hands and feet that sometimes occurs during the night (when muscles are inactive) yet goes away soon after walking

Nonspecific Physical or Anatomical Barriers

• Built-in defenses in skin - Outermost layer of skin (Stratum Corneum) with epithelial cells compacted/cemented together, and impregnated with protein, Keratin* = thick, tough layer that is impervious and waterproof - Flushing effect of sweat glands also helps remove microbes • Built-in defenses in mucous membranes - Coating of digestive, genitourinary, and respiratory tracts are moist and permeable - Despite normal wear and tear, damaged epithelia cells are rapidly replaced - Mucous coat impedes attachment and entry of bacteria - Blinking and tear production flush the eye surface and rids of irritants - Flow of saliva helps carry microbes into the harsh conditions of stomach - Flushing effect of urination, defecation, vomiting also evacuate Noxious* substances or microorganisms from the body - Anti-Microbial Effect* - Sebum, saliva, and tears - Respiratory Tract: Ciliary defense of respiratory tree - nasal hair traps larger particles Ex) Rhinitis - inflammation of the nasal mucosa ofeten seen w/ allergy/colds, creates copious flow of mucus and fluids that helps to flush out nasal passageways Ex) Respiratory tree (trachea/bronchi) - ciliated epithelium (ciliary escalator) converys forgein particles entrapped in mucus toward the pharynx to be removed Ex) Irritation of the nasal passage reflexively initiates a sneeze that expels a large volume of air at high velocity Ex) Acute sensitivity of bronchi, trachea, larynx to foreign matter triggers coughing that ejects irritants • Normal microbiota presence can also block access of pathogens to epithelial surfaces - Compete with pathogens for limited resources or alter environment of the body Ex) Bacterial residents of large intestine secrete bacteriocins or ATBs that can inhibit or kill other bacteria

C-Reactive Protein (CRP)

• CRP - pattern recognition receptor that is an early indicator of inflammation - A large protein synthesized by the liver that circulates in the blood - Released in response to cytokines produced by macrophages during infections and other pathologic conditions - Attached to PAMPs and other receptors on dead or injured body cells and infectious agents = increases phagocytosis and promotes the complement system - Serves as a source of localized, immediate, innate protection - Can be detected within the first few hours of the onset of inflammation = effective marker for inflammation and can be measured with blood tests - Elevated levels of CRP can also be found in cardiovascular disease, cancer, tissue injury, and necrosis (often used to DX risks for these) • Edema* - accumulation of fluid gives rise to local swelling and hardness - Capillaries become leaky under the influence of cytokines - plasma that escapes from small vessels into the tissues is called exudate* > accumulation of this fluid = edema • Edematous exudate contains: plasma proteins (globulins, albumin), the clotting protein (fibrinogen), blood cells, and cellular debris - Exudate can be clear (serous) or may contain RBCs or pus* Pus - composed of mainly WBCs, microbes, and debris from phagocytosis

Artificial Active Immunity

• Can be conferred artificially by vaccination- deliberately exposing a person to material that is antigenic but not pathogenic - Principle is to stimulate a primary and secondary anamnestic response to prepare the immune system for future exposure to a virulent pathogen - Response to a future exposure will be immediate, powerful, and sustained

Vascular Changes: Chemical Mediators, Cytokines, Chemokines

• Chemical Mediators - small molecules that are released during inflammation and specific immune reactions that allow communication between cells of the immune system and facilitate surveillance, recognition, and attack • Cytokines* - chemical substance produced by WBCs and tissue cells that regulates development, inflammation, and immunity - Released by blood cells, tissue cells, and platelets in the injured area • Vasoactive mediators - affect the smooth muscle cells surrounding veins and arteries, changing the flow of blood to the area by causing constriction or dilation of vessels • Chemotactic factors/Chemokines - chemical mediators that stimulate the movement and migration of WBCs • Inflammatory mediators cause fever, stimulate lymphocytes, prevent infection spread, and cause allergic symptoms Ex) Constriction if 1st stimulated, lasts for a few seconds/minutes - once clot has formed to prevent blood loss, it is followed in quick succession by the opposite reaction = vasodilation - Vasodilation - to increase the flow of blood into the area which facilitates the influx of immune components and also causes redness and warmth (rubor and calor)

Functions of MHC Groups

• Class I MHC- genes code for markers that display unique characteristics of self and allow recognition of self molecules* and regulation of immune reactions - Display unique characteristics of self which is important to the process of tissue rejection* - Required for T lymphocytes to interact with pathogens - all nucleated cells possess Class I molecules. • Class II MHC - genes code for immune regulatory receptors found on Antigen- Presenting Cells* (APCs): macrophages, dendritic cells, and B cells - Involved in presenting antigen to T-cells • Only "professional" antigen presents = possess both class I and II receptors necessary for interactions with T cells

Cytotoxic T Cells

• Cytotoxic T (Tc) cells (also called CD8 cells and killer T cells) - They express CD8 receptors and are activated by antigen/MHC I - Destroy foreign or abnormal cells by secreting perforins and granzymes* (cytotoxic enzymes produced by cytotoxic T cells and NK cells that participate in cell death) • Must recognize a foreign peptide carried by an MHC-I receptor and mount a direct attack upon the target cell to become activated • Perforins - proteins that can punch holes in the membranes of target cells • Granzymes - enzymes that digest proteins • Perforins cause ions to leak out of target cells and create passage for granzymes to enter • Granzymes induce loss of selective permeability > target cell death through process called Apoptosis* • Apoptosis* - is genetically programmed for destruction of nucleus and complete cell lysis and death Target cells that can be destroyed by TC cells**: • Virally* infected cells - cytotoxic cells recognize and react against other cells that carry virus peptide MHC combinations expressed on their surface; defenses are essential protection against viral infections • Cancer* cells - T cells constantly survey the tissues and immediately attack any abnormal cells they encounter; importance of this function is clearly demonstrated in the susceptibility of T-cell-deficiency people to cancer • Cells from other animals and humans - cytotoxic CMI is the most important factor in graft rejection*; Tc cells attack the foreign tissues that have been implanted into a recipient's body

Genetically Engineered Vaccines

• DNA vaccines - create recombination by inserting microbial DNA into plasmid vector • Human cells pick up the plasmid and express the microbial DNA as proteins causing B and T cells to respond, be sensitized, and form memory cells - Experimental vaccines for Lyme disease, hepatitis C, herpes simplex, influenza, tuberculosis, malaria 1) DNA that codes for protein antigen is extracted from pathogen genome. 2) Genomic DNA is inserted into plasmid vector; plasmid is amplified and prepared as vaccine. 3) DNA vaccine is injected into subject. 4) Cells of subject accept plasmid with pathogen's DNA. DNA is transcribed and translated into various proteins. 5) Foreign protein of pathogen is inserted into cell membrane, where it will stimulate immune response.

Development of New Vaccines

• Despite considerable successes, dozens of bacterial, viral, protozoan, and fungal diseases still remain w/o functional vaccine • No reliable vaccines are available for: HIV/AIDS, various diarrheal diseases (E.coli, Shigella), a # of respiratory diseases, worm infections - which affect over 200 million people per year worldwide • • •

Specific Events in B-Cell Maturation

• Directed by bone marrow sites that harbor Stromal Cells, which nurture the lymphocyte stem cells and provide hormonal signals • Millions of distinct B cells develop and "home" to specific sites in the lymph nodes, spleen, and GALT • Come into contact with antigens throughout life • Have immunoglobulin as surface receptors for antigens

Proliferative Stage of Lymphocyte Development

• Does not require actual presence of foreign antigens • DOES require the removal of clones of lymphocytes that can react against self MHC antigens - Presence of "forbidden" clones could cause severe damage if the immune system mistakes self molecules as foreign and responds against host's own tissues • Part of the clonal selection theory says that some clones are eliminated during development through clonal deletion - Removal of harmful clones is one basis of Immune Tolerance* (tolerance to self) a) Antigen-Independent Period 1. During development of early lymphocytes from stem cells, a given stem cell undergoes rapid cell division to form numerous progeny. During early cell differentiation, there are random rearrangements of the genes that code for cell surface protein receptors. The result is a large array of genetically distinct cells, called clones, each clone bearing a different receptor to react with only a single type of foreign molecule or antigen. 2. At this time, any lymphocyte clones that carry a specificity for self molecules and could be harmful are eliminated from the pool of diversity. This is a way to achieve immune tolerance. 3. The specificity for a single antigen molecule is programmed into the lymphocyte and is set for the life of a given clone. The end result is an enormous pool of mature but naive lymphocytes that are ready to further differentiate under the influence of their "home" organs and immune stimuli.

Clonal Selection Theory

• Each distinct lymphocyte has an ability to recognize only one specific antigen or epitope* • A conceptual explanation for the development of lymphocyte specificity and variety during immune system maturation* • Lymphocyte specificity is genetically preprogrammed and exists before antigen has ever been encountered. • Clonal Selection Theory - Undifferentiated lymphocytes in embryo and fetus undergo a continuous series of divisions and genetic changes that generate millions of different cell types, each with a particular/unique receptor specificity • Lymphocytes use 500 genes to produce a tremendous variety of specific receptors

Complement Pathways

• End stages all converge at the same point and yield similar end result - destruction of microbe or infected cell • Focus of damage is on the cell membrane, this portion of complement defense is not as effective on microbes whose outer walls block access to the membrane • Effective on cells and viruses with exposed membranes Classical Pathway - Complement-fixing antibodies have rapid, specific effects > C1q, C1r, C1s, Factors C4, C2, C3* - Most specific, activated by presence of antibody bound to microorganism - Links complement to reactions of acquired immunty MB-Lectin Pathway - Mannose-binding lectin (MBL) binds mannose on pathogen surfaces; nonspecific for bacteria and viruses > MBL, MASP-1, MASP-2, Factors C4, C2, C3* - Host serum protein or lectin binds a sugar called mannan present in walls of bacteria/microbes - Nonspecific, triggered by common foreign molecules on the surface of microbes Alternative Pathway - Molecules on surfaces of bacteria viruses and parasites; nonspecific > Factors B, D, and C3* - Initiated by complement proteins that bind to certain surface molecules of microbes (PAMPs) - Nonspecific, triggered by common foreign molecules on the surface of microbes; can also be triggered spontaneously

Erythrocytes and Platelet Lines

• Erythrocytes: produced by stem cells that go through several stages of differentiation and lose their nucleus just prior to entering the circulation - Resultant RBCs are simple, biconcave sacs of HGB that transport O2 and CO2 to/from tissues - Most numerous of circulating cells; appear in stains as small pink cycles - RBCs do NOT ordinately have immune functions, can be TARGET of immune reactions • Platelets: formed elements in circulating blood that are NOT whole cells - Formed by the disintegration of a large, multinucleate cell, the Megakaryocyte* - Blue-gray with fine red granules, are readily distinguished from cells by their small size - Function primarily in Hemostatsis (plugging broken blood vessels to stop bleeding) and in releasing chemicals that act in blood clotting and inflammation

Strategies in Vaccine Design

• Exact antigenic determinants can be used when known: - Capsules - pneumococcus, meningococcus - Surface protein - anthrax, hepatitis B - Exotoxins - diphtheria, tetanus • Antigen can be taken from cultures, produced by genetic engineering, or synthesized • Insert genes for pathogen's antigen into plasmid vector, and clone them in an appropriate host - Stimulated clone host to synthesize and secrete a protein product (antigen), harvest and purify the protein - hepatitis • "Trojan horse" vaccine - genetic material from a pathogen is inserted into a live carrier nonpathogen; the recombinant expresses the foreign genes - Experimental vaccines for AIDS, herpes simplex 2, leprosy, tuberculosis

VACCINATION / Principles of Vaccine Preparation

• Exposing a person to the antigenic components of a microbe without its pathogenic effects for the purpose of inducing a future protective response* • The basic principle behind vaccination is to stimulate a primary response that primes the immune system for future exposure to a virulent pathogen* • Most vaccines are prepared from: - Killed whole cells or inactivated viruses - Live, attenuated cells or viruses - Antigenic molecules derived from bacterial cells or viruses - Genetically engineered microbes or microbial agents

Functions of the Fc (crystallizable fragment) Fragment

• Fc fragment binds to cell membranes - macrophages, neutrophils, eosinophils, mast cells, basophils, lymphocytes • Regions on the Fc portion in certain antibodies fix complements - Binding of Fc may cause release of cytokines • •

Fever: An Adjunct to Inflammation

• Fever - abnormally elevated body temp - Also associated with Allergies, Cancers, other organic illnesses** - Body temp maintained by hypothalamus region in the brain = regulates body heat production and loss - Core temp is around 37C • Fever is initiated by circulating Pyrogens* which reset the hypothalamus to increase body temperature; signals muscles to increase heat production and vasoconstriction • Pyrogens (Exogenous = outside) - products of infectious agents i.e. viruses, bacteria, protozoans, fungi - Endotoxin - lipopolysaccharide found in the cell walls of gram(-) bacteria - Blood, blood products, vaccines, or injectable solutions can also contain exogenous pyrogens • Pyrogens (Endogenous = inside) - liberated by monocytes, neutrophils, and macrophages during phagocytosis - Macrophages release 2 potent pyrogens interleukin-1 (IL-1) and tumor necrosis factor (TNF) • Chills? = brain reacts to pyrogen

T-Cell Receptors for Antigen

• Formed by genetic recombination like B-cell receptors, with variable and constant regions • 2 parallel polypeptide chains • Unlike B-cell receptors, T-cell receptors are small, not secreted

Nonspecific Chemical Defenses

• From skin and mucous membranes - Secretions from Sebaceous* glands in the skin exert antimicrobial effect - Specialized glands (i.e. Meibomian Glands of the eyelids) lubricate the conjunctiva with an antimicrobial secretion • Other defenses in tears, saliva and skin: - Lysozyme* - an enzyme that hydrolyzes the peptidoglycan in the cell wall of bacteria - Defensins* - peptides that produce cells/tissues that damage cell membranes and lyse bacteria and fungi - Skin cells produce defensin called Dermicidin* that helps eliminate bacteria - Paneth cells in the intestine secrete defensins that can destroy or inhibit several types of infectious agents - High lactic acid, electrolyte concentration in sweat, skin's acidic pH and fatty acid content are inhibitory to many microbes - Hydrochloric acid in stomach protects against pathogens that are swallowed - Digestive juices and bile of intestines are destructive to some microbes - Semen contains an antimicrobial chemical that inhibits bacteria - Vagina has protective acidic pH (maintained by lactobacilli)

Genetic Defenses

• Genetic makeup of a person is different enough to ensure protection from some pathogens • Some pathogens have such great specifity for one host SPECIES* that they are incapable of infecting others - "Humans can't acquire distemper from cats, and cats can't get mumps from humans" • Viruses have great specificity for their specific host receptors Ex) Newcastle virus may kill your parrot while you are safe; okay to cuddle your dog recovering from mumps - However is not true for zoonotic infectious agents that attack a broad spectrum of animals • Some genetic differences in susceptibility exist for other pathogens, including differences within members of the same species - Humans carrying a mutation of gene or genes for sickle-cell anemia are resistant to malaria - Genetic differences in susceptibility exist also to TB, leprosy, and certain systemic fungal infections

Agranulocytes: Lymphocytes - B Cells, T Cells, Antibodies

• Globular, nonlobed nuclei and lack prominent cytoplasmic granules; appear small, spherical cells w/ uniformly dark, rounded nucleus surrounded by a thin fringe of clear cytoplasm • Cornerstone of the 3rd line of defense • 2nd most common WBC in the blood (20-35% of total circulating leukocytes); 1/10th of all adult body cells are lymphocytes (exceeded only by erythrocytes, fibroblasts) 2 Types of Lymphocytes (key cells in the 3rd line of defense): - When stimulated by foreign substances (antigens), Lymphocytes are transformed into activated cells that neutralize and destroy those substances - Both display specificity and memory (key characteristics of immune system) 1. B Lymphocytes (B cells) - produced in the bone marrow; transported by the bloodstream and lymph, move freely between lymphoid organs and connective tissues - Form specialized plasma cells and secrete antibodies* - Activated B cells form specialized plasma cells that produce Antibodies* - Antibodies are proteins that bind to foreign cells or molecules and participate in their destruction - B cells contribute to Antibody-Mediated Immunity (Humoral Immunity)* - Following stimulation by antigen, B cells differentiate either into plasma cells, which produce and secrete antibodies* or into memory cells* which will react rapidly if the antigen is encountered at some point in the future** 2. T Lymphocytes (T cells) - produced in the bone marrow BUT mature in the Thymus gland; transport is the same as B cells - Modulate immune functions and kill foreign cells* - Activated T cells engage in spectrum of immune functions called Cell-mediated Immunity* = killing foreign cells directly and exerting control over immune function • Natural Killer Cells (NK) - develop from the same precursor as T and B cells but follow a different developmental path - Unlike B/T cells, NK cells NEVER develop specificity for a single antigen and are generally NOT considered part of the 3rd like of defense

Blood Cells

• Hemopoiesis (or hematopoiesis) - production of blood cells - begins in early embryonic development in the yolk sac (embryonic membrane), later taken over by the liver and lymphatic organs, then finally assumed entirely/permanently by red bone marrow • Relatively short life of blood cells demands a rapid turnover that is continues throughout human life • Pluripotential Stem Cells* - primary precursor of new blood cells, pool of undifferentiated cells - maintained in the marrow - During development, stem cells proliferate and differentiate = immature or unspecialized cells develop the specialized form and function of mature cells - Primary lines of cells that arise from this process produce: RBCs, WBCs/Leukocytes, Platelets/Thrombocytes - WBC lines are programmed to develop into several secondary lines of cells during the final process of differentiation - These committed lines of WBCs are largely responsible for immune function • Leukocytes (WBC) - are evaluated by their reactions with a hematologic stain that contains a mixture of dyes and can differentiate cells by color and morphology - When this stain is used on blood smears and light microscope = appear either with or w/o noticeable colored granules in the cytoplasm - They are divided into 2 groups: Granulocytes and Agranulocytes ▪ Granulocytes: lobed nucleus ▪ Agranulocytes: unlobed, rounded nucleus

Vasoactive Mediators

• Histamine - vasoactive mediator produced by mast cells and basophils - Causes vasodilation, increased vascular permeability, and mucus production - Primary function in inflammation and allergy • Serotonin - mediator produced by platelets and intestinal cells - Causes smooth muscle contraction, inhibits gastric secretion, acts as a neurotransmitter • Bradykinin - vasoactive amine from the blood or tissues - Stimulates smooth muscle contraction and increases vascular permeability, mucus production, and pain - Active in allergic reactions

Antibody Structure and Functions

• Immunoglobulins (Ig): molecule with 4 polypeptide chains connected by disulfide bonds • All antibodies have two functionally distinct segments (fragments): - Antigen binding fragments (Fabs) "arms" with their amino-terminal end (variable regions of the heavy and light chains) as antigen-binding sites - Crystallizable fragment (Fc)* binds to various cells and molecules of the immune system

Structure and Function of the Organs of Defense and Immunity

• Immunology: study of the body's 2nd and 3rdlines of defense • Primary functions of a healthy immune system: 1. Surveillance of the body (organs, tissues, other compartments) 2. Recognition and differentiation of normal versus foreign material i.e. pathogens 3. Attack against and destruction of entities deemed to be foreign invaders • The cells of the immune system constantly move about the body, surveying the tissues for potential pathogens - Carried out by WBCs/Leukocytes* - have innate capacity to recognize and differentiate any foreign material in the body i.e. invading bacterial cells - Foreign matter is often referred to as Nonself* - Normal cells of the body are called Self* - monitored and recognized, usually not attacked by immune system = central to effectiveness • Foreign cells must be recognized as potential threat and dealt with • Normal, healthy cells should not come under attack - Exceptions would be abnormal or damaged self cells i.e. cancer cells

Cytokines

• Important groups of cytokines and other mediators and their major functional types: 1. cytokines that mediate nonspecific immune reactions i.e. inflammation and phagocytosis 2. cytokines that regulate the growth and activation of lymphocytes 3. cytokines that activate the immune reactions during inflammation 4. hematopoiesis factors for WBCs 5. vasoactive mediators 6. miscellaneous inflammatory mediators

Development of Lymphocytes

• In the bone marrow, lymphocytic stem cells differentiate into either T or B cells - B cells stay in the bone marrow while T cells migrate to the thymus - Both T and B cells migrate to secondary lymphoid tissue - Secondary lymphoid tissues will constantly be resupplied with B and T cells • When B+T cells reach the lymphoid tissue, each are already equipped to respond to a single unique antigen - generated by rearrangements of the gene segments that code for the antigen receptors on T+B cells • Each genetically unique line of lymphocytes from this process is called a Clone* - All the cells in a clone display identical protein receptors on their surface = will reach with one specific antigen • During lymphocyte development, there is a huge diversity of possible lymphocytes, each with distinct antigen-specific receptors, that results from extensive rearrangements* of the gene fragments that code for T and B cells*

Herd Immunity

• Individuals immune to a communicable infectious disease will not harbor it = reducing the occurrence of that pathogen • With larger number of individuals in a population (herd), it will be less likely that an unimmunized member of the population will encounter the agent and become infected • Collective immunity through mass immunization confers indirect protection on the nonimmune members (i.e. infants too young to be vaccinated) • Most ineffective herd immunity outcome occurs when the healthiest members are vaccinated

Reticuloendothelial System (RES) / Reticular System

• Network of connective tissue fibers that originate in the cellular basal lamina, interconnect nearby cells, mesh with massive connective tissue network surrounding organs • This network / Mononuclear Phagocyte System (MPS) is critical to immune function because it provides a passageway within and between tissues and organs • Inhabited by Phagocytic cells* - mononuclear phagocyte system - macrophages ready to attack and ingest microbes that passed the first line of defense

Late Reactions / Downside of Inflammation

• Inflammatory reactions that last more than a few days attract monocytes, lymphocytes, and macrophages to the reaction site • Macrophages clear pus, cellular debris, dead neutrophils, damaged tissue (engulf and dispose large masses) - B lymphocytes react with foreign molecules and cells by producing specific antimicrobial proteins (antibodies) - T lymphocytes kill intruders directly • Late in the process - tissue undergoes various levels of repair and may be replaced by connective tissue in the form of a scar • If inflammation cannot be relieved or resolved, can become chronic and create long-term conditions: • Inflammatory exudates that build up in the brain in African trypanosomiasis, cryptococcosis, and other brain infections can be so injuries to the nervous system that impairment is permanent - Inflammatory reactions frequently lead to abscess, a swollen mass of neutrophils and dead, liquefied tissue that can harbor live pathogens in the center - Abscesses are prominent feature of staphylococcal, amebic, enteric infections • Chronic diseases i.e. Tubercles of TB, lesions of late syphilis, disfiguring nodules of leprosy, cutaneous ulcers of leishmaniasis - d/t aberrant tissue response called Granuloma formation* • Granulomas develop in response not only to microbes but also inanimate foreign bodies that are difficult to break down - Condition is initiated when neutrophils and macrophages ineffectively and incompletely phagocytose the pathogens or materials involved in inflammatory reaction - Failure to manage the debris of inflammation = "frustrated phagocytosis" - Macrophages respond by storing ingested materials in vacuoles and becoming inactive - Sites are further infiltrated with lymphocytes - Resultant collections make tissue appear granular - Granuloma can exist in tissue for months, years, lifetime • Tumor necrosis factor (TNF) - regulates wide variety of early immune activities i.e. phagocytosis - Powerful pyrogen - Overproduction of TNF is involved in # of diseases i.e. septic shock, psoriasis, asthma, autoimmunity - Several drugs i.e. adalimumab (Humira), etanercept (Enbrel) have been developed to TX damaging effects of TNF • Promising TX with use of chemokine inhibitors that could reduce chemotaxis and massive, destructive influx of leukocytes (may treat cancers, hardening of arteries, Alzheimer)

Benefits of Edema and Chemotaxis

• Influx of fluids and the infiltration of neutrophils are physiologically beneficial activities • Fluids dilute toxic substances • Fibrin clot can effectively trap microbes and prevent their further spread • Neutrophils that aggregate in the inflamed site are immediately involved in phagocytosing and destroying microbes, dead tissues, and particulate matter • Some types of inflammation - accumulated phagocytes contribute to pus • Certain bacteria (streptococci, staphylococci, gonococci, meningococci) are powerful attractants for neutrophils and are termed - PYOGENIC* = pus-forming bacteria

Cytokines that Regulate Lymphocyte Growth and Activation

• Interleukin-2 - primary growth factor from T cells - Acts on the same cells that secrete it - Stimulates cell division and secretion of other cytokines - In B cells, it is a growth factor and stimulus for antibody synthesis • Interleukin-4 - stimulus for development of B cells and production of antibodies that mediate allergies - Inhibits macrophage actions • Granulocyte colony-stimulating factor (G-CSF) - produced by T cells, macrophages, and neutrophils - Stimulates the activation and differentiation of neutrophils • Macrophage colony-stimulating factor (M-CSF) - produced by variety of cells - Promotes growth and development of stem cells that differentiate into macrophages • Interferon gamma - T-cell-derived mediator whose primary function is to activate macrophages - Promotes the differentiation of T and B cells, activiates neutrophils, and stimulates diapedesis

Requirements for an Effective Vaccine

• It should have a low level of adverse side effects or toxicity and not cause serious harm. • It should protect against exposure to natural, wild forms of pathogen. • It should stimulate both antibody (B-cell) response and cell-mediated (T-cell) response. • It should have long-term, lasting effects (produce memory cells). • It should work with minimal doses or boosters. • It should be inexpensive, have a relatively long shelf life, and be easy to administer.

Killed Vaccines Attenuated Vaccines

• Killed or Inactivated Vaccines - prepared by cultivating the desired strain or strains of a bacterium or virus and treating them with formalin, radiation, heat, or other agent that kills the microbe but does not change its antigenic structure Ex) Vaccine for bacterial disease Cholera Ex) IPV polio vaccine and some forms of Influenza vaccine contain inactivated viruses - Because microbe does not multiply, killed vaccines often require a larger dose and more boosters to be effective • Attenuated Vaccines - attenuation is any process that substantially lessens the virulence of viruses or bacteria - Usually achieved by modifying the growth conditions or manipulating microbial genes in a way that eliminates virulence factors - Methods include: long-term cultivation, selection of mutant strains that grow at colder temps, passage of the microbe through unnatural hosts or tissue culture, removal of virulence genes Ex) Vaccine for TB (BCG) was obtained after 13 years of subculturing the agent of bovine TB Ex) Vaccines for measles, mumps, polio (oral vaccine), rubella contain active/non-virulent viruses • Advantages of live preparations are: - Organisms can multiply and produce infection (but not disease) like the natural organism - They confer long-lasting protection - Usually require fewer doses and boosters • Disadvantages include: - Require special storage, can be transmitted to other people, can conceivably mutate back to virulent strain • Subcellular / Acellular Vaccines - vaccines made from bacterial cell parts • Subunit Vaccines - isolated from viruses - Antigens used in these vaccines may be extracted from cultures of the microbes, produced by engineering, or synthesized chemically • Examples of extracted antigens - capsules of pneuomococcus and meningococcus, protein surface of antigen of anthrax, surface proteins of hep B virus • Toxoid - special type of vaccine, consists of a purified fragment of bacterial exotoxin that has been inactivated - By eliciting the production of antitoxins that can neutralize the natural toxin, toxoid vaccines provide protection against toxinoses i.e. diphtheria, tetanus

Agranulocytes: Monocytes/Macrophages

• Largest of all WBCs and 3rd most common in circulation (3-7%) • As it matures, nucleus becomes oval or kidney shaped (indented on one side), off center, often contorted w/ fine wrinkles • Discharged by the bone marrow into the bloodstream, where they live as Phagocytes* for a few days then leave the circulation to undergo final differentiation into Macrophages* - key players in immunity Macrophages are responsible for: - many types of specific and nonspecific phagocytic and killing functions (assume job of cellular housekeepers, "mopping up the messes" created by infection and inflammation) - processing foreign molecules and presenting them to lymphocytes - secreting biologically active compounds that assist, mediate, attract, and inhibit immune cells and reactions • Dendritic Cells - another product of monocyte cell line; named for their long, thin cell processes - Immature dendritic cells move from the blood to the mononuclear phagocyte system and lymphatic tissues (trap pathogens) - Ingestion of bacteria and viruses stimulates dendritic cells to migrate to lymph notes and the spleen to participate in reactions with lymphocytes

Lymphatic Fluid / Lymphatic Vessels

• Lymph is a plasma-like liquid carried by lymphatic circulation - Formed when blood components move out of blood vessels into extracellular spaces and diffuse or migrate into the lymphatic capillaries - Made up of water, dissolved salts and 2-5% proteins (especially antibodies and albumin) - Transports white blood cells (especially lymphocytes), fats, cellular debris, and infectious agents that have gained access to the tissue spaces - RBCs are not normally found in lymph • System of vessels that transport lymph is constructed along the lines of blood vessels - Lymphatic capillaries permeate all parts of the body except the CNS, bone, placenta, and thymus - Thin walls easily permeated by extracellular fluid which is then moved through contraction of skeletal muscles - Functions to return lymph to circulation; flow is one-direction - toward the heart - eventually returning to blood stream Ex) Parasitic Infection Filariasis - when the lymphatic drainage is blocked by infectious agents - Filarial worms from the infection become caught in the lymph nodes and channels of the extremities and plug them up - Prevents the lymph from flowing into the accessory ducts and back to the circulation - Buildup of lymph massively distorts limbs and other body parts i.e. scrotum, breasts

Specific Events in T-Cell Maturation

• Maturation is directed by the thymus gland and its hormones • Different classes of T-cell receptors termed Clusters of Differentiation (CD receptors)* or clusters of differentiation • Clusters of differentiation (CD) receptors are molecules on the surfaces of T cells that act as receptors and may also be involved in cell adhesion and communication** • CD molecules serve multiple roles as cell receptors and may be involved in cell adhesion and communication in variety of cells - CD4 on T helper (TH) cells - CD8 on T cytotoxic (Tc) cells • Mature T cells migrate to lymphoid organs

Second-Line Defenses: Inflammation / Inflammatory Response

• Mechanisms that play important roles in host defenses: 1. Recognition 2. Inflammation 3. Phagocytosis 4. Interferon 5. Complement • Primarily nonspecific in their effects but also support and interact with the specific immune responses • Inflammation* - Reaction to any traumatic event in the tissues that attempts to restore homeostasis - Helps to clear away invading microbes and cellular debris left by immune reactions - Redness (rubor) - increased circulation and vasodilation in response to chemical mediators - Warmth (calor) - heat given off by the increased blood flow - Swelling (tumor) - increased fluid in the tissue as blood vessels dilate - edema; WBC's, microbes, debris, and fluid collect to form pus; prevents spread of infection - Pain (dolor) - stimulation of nerve endings from pressure of swelling or chemical mediators - Loss of function (sometimes added for a complete picture of effects that can accompany inflammation • Serve an important warning that injury has taken place and will set in motion responses that can save the body from further injury • Factors that can elicit an inflammatory response include trauma from infection*, tissue injury or death, and specific immune reactions; main functions: 1. To mobilize and attract immune cells and chemicals to the site of the injury 2. To set in motion mechanisms to repair tissue damage and localized and clear away harmful substances 3. To destroy and block microbes from further invasion • Inflammatory response is a powerful defensive reaction and means for the body to maintain stability and restore itself after an injury - But when chronic*, has potential to actually cause tissue injury, destruction, and disease

Immunization: Providing Immune Protection Through Therapy IMMUNOTHERAPY*

• Methods that actively or passively immunize people are widely used in disease prevention and treatment • Active immunization (a person is administered some form of antigen) is synonymous with vaccination • Passive immunization (a person is given antibodies) is a type of Immunotherapy* • Immunotherapy - preventing or treating infectious diseases by administering substances that produce artificial immunity; may be active or passive - medical procedure that may involve the transfer of premade antibodies to protect the individual** - Preventing or treating infectious diseases by administering substances such as premade antibodies that produce artificial immunity**

Routes of Administration and Side Effects of Vaccines

• Most vaccines are injected by SQ, IM, ID • Few vaccines are oral and have advantages - oral dose of a vaccine can stimulate protection IgA on the mucous membrane of the portal of entry - Also are easier to give, more readily accepted, well tolerated • Intranasal Vaccine - delivered into the nose by aerosol or drops (FluMist) and skin patches • Adjuvant - any compound that enhances immunogenicity and prolongs antigen retention at the injection site - Precipitates the antigen and holds it in the tissues so that it will be released gradually - Gradual release presumably facilitates contact with antigen-presenting cells and lymphocytes Ex) alum (aluminum hydroxide salts), Freund's complete adjuvant (emulsion of mineral oil, water, extracts from mycobacteria), beewax • Stringent requirements for development of vaccines • More benefit than risk • Possible side effects include local reaction at injection site, fever, allergies; rarely back-mutation to a virulent strain, neurological effects • When known or suspected adverse effects have been detected, vaccines are altered or withdraw

Associated Lymphoid Tissue: MALT, GALT

• Mucosal-Associated Lymphoid Tissue (MALT) - embedded throughout systems lined with mucous membranes are discrete bundles of lymphocytes and other WBCs - Widespread positioning provides a local, rapid mechanisms for responding to the constant influx of microbes entering via the GI, respiratory, urinary, and other portals of entry - Pharynx houses a prominent source of MALT in the form of Tonsils* - Breasts of pregnant lactating women also become temporary sites of lymphoid tissues that add protective antibodies to breast milk -MALT is further divided into more than a dozen categories, based on where the specific lymphoid tissue is found - Most important example - gut-associated lymphoid tissue = GALT • Gut-Associated Lymphoid Tissue (GALT)(Peyer's Patches) - includes the appendix and preyer's patch, compact aggregations of lymphocytes in the ileum of the small intestine - Provides immune functions against intestinal pathogens - Significant source of some types of antibodies - Less well-organized collections of secondary lymphoid tissue include: skin-associated lymphoid tissue, bronchial-associated lymphoid tissue

Natural Killer (NK) Cells Natural Killer T (NKT) Cells

• NK cells - Type of lymphocyte related to T cells - Circulate through the spleen, blood, lungs - 1st killer cells to attack cancer cells and virus-infected cells - Destroy cells similar to cytotoxic T cells - Lack antigen receptors = not specific for a single antigen = NOT specific, cell-mediated immune response • NKT cells - have properties of both T cells and NK cells - Express T-cell receptors and NK cell markers and are stimulated by both self and nonself lipids - Once stimulated - produce cytokines, granzymes, and perforins - Important role in regulation of immune reactions against pathogens and tumors and autoimmune and metabolic disorders

Major Categories of Phagocytes

• Neutrophils - general-purpose phagocytes that react early in the inflammatory response to bacteria and other foreign materials and to damaged tissue - Polymorphonuclear phagocytic cells* - Common sign of bacterial infection is high neutrophil count (neutrophilia) - Primary component of pus - A "Workhorse" of innate immunity - Have distinct system for capturing pathogens called "Neutrophil Extracellular Traps" or NETS - Programmed to die after they have gone through their regular engulfment and killing of bacteria/pathogens - Death does not end their protective actions - Dying neutrophils throw out fibrous matrix composed of DNA, enzymes, histones, and other cell contents that continue to stop invading microbes even after neutrophils are completely lysed - NET works at several levels to trap and immobilize bacteria/fungi and degrade their virulence factors, kill them w/ microbicidal chemicals, preventing from spreading • Eosinophils - attracted to sites of parasitic infections and antigen-antibody reactions; minor phagocytic role - Attack and destroy large eukaryotic pathogens*

Granulocytes: Neutrophils, Eosinophils, Basophils

• Neutrophils - lobed (up to 5) nuclei with fine, pale lavender granules; also called Polymorphonuclear Neutrophils (PMNs) - Polymorphonuclear phagocytic cells* - Make up 55-90% of circulating Leukocytes, about 25 billion cells in circulation at any given moment - Main work is PHAGOCYTOSIS - High numbers in blood/tissue = constant challenge from resident microbiota and environmental sources - Lifespan = 2 days • Eosinophils - distinguished by large, orange to red (eosinophilic) granules and bilobed nucleus - Attack and destroy large eukaryotic pathogens* - Much more numerous in the bone marrow and spleen than in circulation (1-3% of total WBC count) - Granules contain peroxidase, lysozyme, other digestive enzymes, toxic proteins, and inflammatory chemicals - Main action is ability to attack and destroy large eukaryotic pathogens - Also involved in inflammation and allergic reactions - Most important targets: larval forms of worm parasites that cause ascariasis, filariasis, schistomomiasis - binding of eosinophils to larval surface release toxic compounds into their cells causes disintegration of the larvae - Earliest cells to accumulate near sites of inflammation and allergic reactions (attract other leukoctyes and release chemical mediators) • Basophils - pale=stained, 2-lobed nuclei, very prominent dark blue-black granules - Release histamine during immediate allergies* - Scarcest type of leukocyte (<0.5% of total circulating WBCs in a normal individual - Share some morphological and functional similarities to tissue cells = Mast Cells* - Contain granules with potent chemical mediators that act on cells/tissues of the body Ex) may attract WBC toward the site of a infection or cause blood vessels to dilate in response to an injury *Mast Cells - nonmotile elements bound to connective tissue around blood vessels, nerves, epithelia - Both cell types originate from the same bone marrow stem cell line - Mast cells are first-line defenders against local invasion of pathogens - they recruit other inflammatory cells; are directly responsible for the release of histamine* and other allergic stimulants during immediate allergies

Major Histocompatibility Complex (MHC)

• One set of genes that codes for human cell receptors and plays a role in recognition of self by the immune system* • Set of cell surface proteins (receptors) essential for the acquired immune system in the recognition of self and in rejection of foreign molecules • MHC molecules (receptors) are found on all cells except RBCs • The MHC is also known as the Human Leukocyte Antigen (HLA) system* • Vital role in recognition of self my immune system and rejection of transplanted tissues** • The MHC gene family is divided in two main groups: - MHC Class I genes - MHC Class II genes

Chemotaxis, Binding, and Ingestion Phagolysosome Formation Destruction and Elimination

• Phagocytes migrate into region of inflammation w/ deliberate sense of direction, attracted by gradient of stimulant products from the pathogen and host tissue at the site of injury • Using TLRs receptors that recognize and bind pathogen-associated molecular pattern (PAMPs) receptors - Exposed end of receptor hooks onto a PAMP and dimerizes/joins with 2nd TLR to encase the molecule - This relays a signal into nucleus that stimulates the intracellular phagocytic processes and release of chemical mediators • Phagocytes trap cells or debris against the fibrous network of connective tissue or the wall of blood and lymphatic vessels - Once phagocyte has "caught" its prey, it extends pseudopods that enclose the cells or particles in a pocket and internalize them in a vacuole called a Phagosome* • Lysosomes* migrate to the scene of the phagosome and fuse with it to form a Phagolysosome* - Granules containing antimicrobial chemicals are released into the phagolysosome - forms brew designed to poison, dismantle ingested material - Destructiveness of phagocytosis by death of bacteria within 30 min after contacting the battery of antimicrobial substances • Destructive chemicals await microbes in the phagolysosome • O2-Dependent System (Respiratory Burst / Oxidative Burst)* - elaborates products of O2 metabolism called ROIs - Reactive Oxygen Intermediate (ROIs)* - any charged O2 radical (i.e. superoxide ions, peroxide) given off during O2 metabolism that can be toxic to microbial and other cells • Myeloperoxidase (enzyme in granulocytes) - forms halogen ions (OCl-) that are strong oxidizing agents • Other products of O2 metabolism i.e. H2O2, superoxide anion (O2-), activated or singlet O2 (1O-), Hydroxyl free radical (HO) seperately/together have formidable killing power - Deliver "knockout" punch necessary to kill AEROBIC pathogens i.e. fungi, many bacteria • Other chemicals include: lactic acid, lysozome, and nitric oxide - power mediator that kills bacteria and inhibits viral replication • Cationic proteins that injure bacterial cell wall and number of Hydrolytic* enzymes complete the job • Undigestible debris are released from the macrophage exocytosis

Phagocytosis

• Phagocytes move through the tissues to seek, capture, and destroy targets • General activities of phagocytes: 1. To survey tissue compartments and discover microbes, particulate matter (dust, carbon particles, antigen-antibody complexes), and dead or injured cells 2. To ingest and eliminate these materials 3. To extract immunogenic information (antigens) from foreign matter • Main phagocytic cells*: Macrophages Neutrophils Dendritic cells Monocytes • Major stages of Phagocytosis*: 1. Chemotaxis 2. Adhesion of pathogen 3. Ingestion 4. Phagolysosome formation 5. Destruction 6. Elimination of debris

Phagocytic Recognition

• Phagocytosis = "eating cell process" • Engulfment, attack and dismantle foreign cells using antimicrobial substances • Can occur as isolated even by 1 phagocytic cell responding to minor irritant part of orchestrated events of inflammation • Events in phagocytosis: chemotaxis, phagolysosome formation, destruction, and elimination • Protein receptors within cell membrane of macrophages, called Toll-like receptors (TLRs) • Detect foreign molecules and signal the macrophage to produce chemicals to stimulate an immune response

Lymphoid Organs and Tissues

• Primary organs - Thymus Gland, Bone Marrow - Locations where lymphocytes are formed or reside - Sites of origin and maturation of lymphocytes - WBCs with specific immune function - Subsequently release these cells to populate secondary lymphatic sites • Secondary organs and tissues - Lymph Nodes, Spleen, Mucosal-Associated Lymphoid Tissue (MALT), Gut-Associated Lymphoid Tissue (GALT)(Peyer's Patches) - Circulatory-based locations where encounters with microbes and immune response often take place - Associated lymphoid tissues are collections of cells widely dispersed throughout body tissues i.e. skin, mucous membranes - ready to react with any locally entering infectious agents

Monitoring Antibody Production over Time: Primary and Secondary Responses to Antigens

• Primary response - after 1st exposure to antigen or immunogen - A latent period - marked by lack of antibodies for that antigen - Antigen is being concentrated in lymphoid tissue and is being processed by the correct clones of B lymphocytes - Plasma cells synthesize antibodies, serum titer increases to a certain plateau and then tapers off to a low level over a few weeks or monts - The first antibody to appear is IgM, followed later by IgG arising from activation of the first memory cells. • Secondary response - when exposed again to the same antigen or immunogen within weeks/months/years - Rate of antibody synthesis, peak titer, and length of antibody persistence are increased - Rapidity and amplification are attributed to memory B cells that were formed during primary response - Also called Anamnestic Response* = because of its association with recall - the anamnestic response has NO latent period* - Recall effect shortens the latent or lag period and yields a faster, stronger, and longer-lasting antibody response - Main factors in creating anamnestic effect are that the memory B cells do not have to go through the early steps in activation and do not require as many signals to form plasma cells • Advantage of this response: provides quick and potent strike against subsequent exposures to infectious agents - Memory effect is the fundamental basis for vaccine boosters* • Titer6 - concentration of antibodies - how immune system reactions to an antigen by studying levels of antibodies in serum over time - level is expressed quantitively as titer6

Antibody-Antigen Interactions

• Principle activity of antibodies: unite with, immobilize, call attention to, or neutralize the Ag for which it was formed - Opsonization* - process of coating microorganisms or other particles with specific antibodies so they are more readily recognized by phagocytes. Carried out by antibodies called "opsonins" - Neutralization* - Antibodies fill the surface receptors on a virus or the active site on a microbial enzyme to prevent it from attaching - Agglutination* - Ab aggregation; cross-linking cells or particles into large clumps - Complement fixation* - Activation of the classical complement pathway can result in the specific rupturing of cells and some viruses - Precipitation* - Aggregation of particulate antigen

Miscellaneous Inflammatory Mediators

• Prostaglandins - produced by most body cells - Complex chemical mediators that can have opposing effects i.e. dilation or constriction of blood vessels - Powerful stimulants of inflammation and pain • Leukotrienes - stimulates the contraction of smooth muscle and enhance vascular permeability - Implicated in the more severe manifestations of immediate allergies (constriction of airways) • Platelet-activating factors - substance released from basophils - Causes the aggregation of platelets and the release of other chemical mediators during immediate allergic reactions

T Cells and Superantigens

• Reaction has drastic consequences • Superantigens are found orimarily in bacteria and viruses, and are a form of virulence factor - Enterotoxin from pathogenic staphylococci, certain toxins of group A streptococci, and proteins of Epstein-Barr virus • Provoke overwhelming immune responses by large numbers of T cells regardless of specificity** - Release of massive amount of cytokines - Blood vessel damage - Toxic shock - Multiorgan failure

Antibodies in Serum

• Regardless of the site where antibodies are first secreted, a large quantity eventually ends up in the blood - Antiserum*: serum containing specific antibodies • If separated by electrophoresis, globulins in antiserum separate into 4 bands: - Alpha-1 (α1), alpha-2 (α2), beta (β), and gamma (γ) • Most are antibodies • Gamma globulin (γ) is composed primarily of IgG • β and α2 globulins are a mixture of IgG, IgA, and IgM

T Regularly (Treg) Cells Gamma-Delta T Cells

• Regulatory T cells - express CD4 and CD25 receptors and prevent the immune system from overreacting - Important role in moderating inflammation, allergy, autoimmunity, and helping to ensure that the immune system doesn't target the body's normal microbiota • Gamma-Delta T cells - both Nonspecific and Specific immune responses - Bind to certain PAMPs on microorganisms in a manner similar to nonspecific WBCs like macrophages and dendritic cells - Display characteristics of a specific response as cells possess T-cell receptors which are rearranged to recognize a wide variety of antigens and produce memory cells when activated - acting like a "traditional" T cell - Biology is unclear - but known to be active against certain bacterial pathogens and tumor cells

Clonal Selection and Expansion (2nd stage of development)

• Requires stimulation by antigens i.e. those that come from microbes 2 Important generalities can derive from clonal selection theory: 1. Lymphocyte specificity is preprogrammed, existing in the genetic makeup before an antigen has ever entered the tissues 2. Each genetically distinct lymphocyte expresses only a single specificity and can react to only one type of antigen • First introduction of each type of antigen into the immune system "selects" a genetically distinct lymphocyte (clone) • This contact causes the clone to expand, through mitotic divisions, into a larger population of lymphocytes that can react to that antigen (same single specificity) b) Antigen-Dependent Period 4. Lymphocytes migrate home to the lymphatic organs where they are situated to encounter antigens. Entry of a specific antigen selects only the lymphocyte clone or clones that carry matching surface receptors. This will trigger an immune response, which varies according to the type of lymphocyte involved.

Components and Connections of the Immune System

• The immune system is a large, complex, and diffuse network of cells and fluids that penetrate into every organ and tissue • The body is partitioned into fluid-filled spaces = intracellular, extracellular, lymphatic, cerebrospinal, circulatory compartments - structures and position permit extensive interchange and communication • Body compartments that participate in immune function*: 1. Reticuloendothelial system (RES) 2. Extracellular fluid (ECF) - spaces surrounding tissue cells 3. Bloodstream 4. Lymphatic system 5. Mononuclear Phagocyte System • For effective immune responsiveness, the activities in one fluid compartment must be conveyed to other compartments • At microscopic level, clusters of tissue cells are in direct contact with reticular fibers that are part of the mononuclear phagocyte system (along w/ blood and lymphatic capillaries) • Bathing of all cells and structures is the ECF - important site of exchange for nutrients and gases • Benefit of Integrated System = NO cell of the body (even the most isolated) is far removed from protection

Overview of Specific Immune Response

• Separate but related activities of the specific immune response: - Development and differentiation of the immune system - Lymphocytes maturation and the nature of antigens - Immune reactions to antigens and the activities of T cells - Immune activities of B cells and the production and actions of antibodies I. Development of the Lymphocyte System - Lymphocytes arise from the same stem cells but differentiate into two distinct cell types early on. T cells mature in the thymus gland and B cells mature in specialized bone marrow sites. Once released, matured cells settle in lymphoid organs and serve as a constant attack force for infectious agents II. Contact with Antigens and III. Presentation by Antigen-presenting Cells (APCs) - Foreign cells bear molecules (antigens) that are recognized and engulfed by APCs such as dendritic cells. For most responses, T helper cells first receive the processed antigen from the APC and go on to activate B and other T cells IVA. Activation of T Cells and IV B. T-cell Responses - An activated T cell forms memory cells and differentiates into helper cells or cytotoxic cells. T-cell immunity is termed cell mediated because the whole T cell acts directly to destroy microbes, rather than by secreting molecules Into the body fluids. VA. B-Cell Responses - A B cell activated by T helper cells undergoes a spurt of cell division, producing memory cells that provide a rapid recall of the antigen, and plasma cells that secrete proteins called antibodies. VB. Humoral Immunity*- Antibodies circulate in fluids (blood, ECF, and lymph) providing humoral immunity. The antibodies react specifically with the antigen and mark it for an enhanced response. *A traditional term for such body fluids is the "humors".

Interferon (IFN)

• Small protein molecules produced by certain* leukocytes and tissue cells in response to viral infection • Produced naturally by certain WBC and tissue cells • Used in therapy against certain viral infections, cancer, and used in immune enhancer • Defense against viruses, microbes and in immune regulation and intercommunication • 3 Major Types are: 1. Interferon alpha - product of lymphocytes and macrophages 2. Interferon beta - product of fibroblasts and epithelial cells 3. Interferon gamma - product of T cells • All produced in response to viruses, RNA, immune products, foreign molecules and antigens • All three types bind to cell surfaces and induce changes in genetic expression of antiviral proteins and inhibit expression of cancer genes, have tumor suppressor effects*** • IFNs alpha and beta stimulate phagocytes • IFN gamma is an immune regulator of macrophages and T and B cells

Complement System

• System of blood proteins enhances the ability of antibodies and phagocytic cells to clear pathogens from an organism* • Complex, multiple-duty system in immune system • Consists of at least 30 proteins released by liver cells, lymphocytes, and monocytes • Form of pattern recognition receptor (PRR) that works in concert w/ inflammation and phagocytosis to destroy a wide variety bacteria, viruses, parasites • Generally nonspecific and innate, also play a role in acquired immune responses 3 Primary Defensive Features: 1. Membrane Attack Complex (MAC) - kills pathogens directly 2. Opsonization - the coating of pathogens with molecules that make them more attractive to phagocytes** 3. Recruitment of inflammatory cells and triggering of cytokine release • Membrane attack function - reactions like blood clotting (1st substance in chem series activates the next and so on until end product is reached)

T Helper Cells

• T Helper (TH) cells (also called CD4 cells) - They express CD4 receptors and are activated by antigen/MHC II - Most prevalent type of T cell in blood and lymphoid organs (65% of population) - Regulate immune reaction to antigens, including other T and B cells - Also involved in activating macrophages and increasing phagocytosis - done directly (receptor contact) and indirectly (releasing cytokines i.e. interlukin-2) which stimulatse primary growth and activation of B + T cells - Interleukin-4,-5,-6,-9,-10,-11,-13 which stimulate development of B cells - Differentiation (TH1 or TH2 cells) depends on what set of cytokines is released from APC - Delayed hypersensitivity (response to allergens) from allergies i.e. hay fever, anaphylaxis

The Role of Antigen Processing and Presentation APC INTERLEUKIN THELPER

• T-cell dependent antigens must be processed by phagocytes called Antigen-Presenting Cells (APC) before their contact with T cells • 3 cell types can serve as APCs: - Macrophages - Dendritic cells (most common) - B cells • APCs modify the antigen; then the antigen is moved to the APC surface and bound to an MHC class II receptor • Antigen presentation involves a direct collaboration among an APC and a T helper cell (TH) - Interleukin-1 (IL-1) cytokine secreted by APC to activate TH(T-Helper) cells** - Interleukin-2 (IL-2) cytokine produced by TH to activate B and other T cells** • T Helper Cells - a class of thymus-stimulated lymphocytes that facilitate various immune activities i.e. assisting the activation of B cells and macrophrages

Antigen-Antibody Binding

• The Fab antigen-binding site is composed of hypervariable regions with an extremely variable amino acid content • The groove of this antigen binding site has a specific three-dimensional fit for the antigen • The specificity of the two Fab sites is identical for each antigen - An Ig molecule can bind antigenic determinants on the same cell or on two separate cells and thereby link the

Cooperation in Immune Reactions to Antigens

• The basis for most immune responses is the encounter between antigens and white blood cells • Lymph nodes and spleen concentrate the antigens and circulate them so they will come into contact with lymphocytes

Overview of the Major Host Defenses

• The body's defenses often work in both parallel and redundant ways to fight pathogens HOST DEFENSES - ▪ Innate, nonspecific: • 1st line of defense: Physical barriers, Chemical barriers, Genetic barriers - The first line of defense is a surface protection composed of anatomical and physiological barriers that keep microbes from penetrating sterile body compartments. • Second line of defense: Inflammatory response, Interferons, Phagocytosis, Complement - The second line of defense is a cellular and chemical system that comes immediately into play if infectious agents make it past the surface defenses. Ex) phagocytes that destroy foreign matter, and inflammation which holds infections in check • Acquired, specific • 3rd line of defense: B and T lymphocytes, antibodies, cytotoxicity - The third line of defense includes specific host defenses that must be developed uniquely for each microbe through the action of specialized white blood cells. This form of immunity is marked by its activity toward specific pathogens and development of memory.

Stages of Inflammation / Inflammatory Response stages

• The inflammatory response is a dynamic sequence of events that can be Acute (lasting from a few minutes to hours) or Chronic (lasting days, weeks, or years) a) Injury/Immediate Reactions: Blood vessels narrow (vasoconstriction); blood clots; and mast cells release chemokines and cytokines into injured area. b) Vascular Reactions: Nearby blood vessels dilate; increased blood flow; increased vascular permeability; increased leakage of fluid forms exudate. c) Edema and Pus Formation: Collection of fluid; edema/swelling; infiltration by neutrophils and formation of pus. d) Resolution/Scar Formation: Macrophages lymphocytes, and fibrolasts migrate in; initiate immune response and repair of injury; scar and loss of normal tissue. Stages**: 1. Chemical mediators are released by tissue cells in response to injury or infection 2. Vasodilation of the blood vessels to increase blood flow 3. Permeability of the capillaries increases, allowing plasma and WBCs to exit the blood vessels into the inflamed tissue 4. WBCs migrate through the tissue spaces toward the actual site of injury or infection 5. Neutrophils clean up the area by phagocytosis of microbes and dead cells; accumulation can contribute to pus 6. Regeneration of the tissue or formation of scar tissue completes the repair process

Lymphocyte Receptors

• The role lymphocytes play in surveillance and recognition is a function of their receptors - B-cell receptors - bind free antigens - T-cell receptors - bind processed antigens together with the MHC molecules on the cells that present antigens to them • Antigens are molecules, so their chemical structures can vary over a very wide range (potentially exhibiting billions of uniquely different structures and shapes) - Sources of antigens include microorganisms and chemical compounds in the environment • Each lymphocyte is genetically programmed to express 1 type* of antigen specific receptor*

Specific Immunities: The Adaptive/Acquired Line of Defense

• Third line of defense - Adaptive or Acquired Immunity - Responsible for long-term protection we develop through infections or vaccinations - Adaptive immunity is needed to prevent life-threatening infections • Adaptive immunity is the product of a dual system of specialized leukocytes - B and T lymphocytes • Immunocompetence - ability of the body to interact with a wide spectrum of foreign substances develops • Antigens - any molecules that can stimulate a SPECIFIC* response by T and B cells - Consist of protein, polysaccharide, and other compounds from cells/viruses - Can also be environmental chemicals - Any exposed or released substance is potentially an antigen even from our own cells • Pathogen-Associated Molecular Patterns (PAMPs) - stimulate responses by phagocytic cells during innate defense response - Molecules shared by many microbes that stimulate a nonspecific response • Difference from Innate Immunity - Adaptive immunity have specificity and memory* - Adaptive/acquired immunity is selective Ex) Antibodies produced against the chickenpox virus during an infection will protect against that virus but no against the measles virus - Memory - lymphocytes have been programmed to recall their 1st engagement w/ an invader and respond rapidly next time during exposure

Thymus Gland / Lymph Nodes / Spleen

• Thymus - Originates in the embryo as 2 lobes in the pharyngeal region that fuse into triangular structure - Located in the thoracic cavity near the tip of the sternum - Size is greatest at birth, continues to exhibit high rates of activity and growth until puberty then shrinks throughout adulthood - Site of T-cell maturation • Lymph nodes - Small, encapsulated, bean-shaped organs along lymphatic channels and large blood vessels of the thoracic and abdominal cavities - Major aggregations of nodes occur in the loose connective tissue of the armpit (axillary nodes), groin (inguinal nodes), and neck (cervical nodes) - Location and architecture of these nodes clearly specialize them for filtering out materials that have entered the lymph and providing appropriate cells and niches for immune reactions • Spleen - Nestled below the diaphragm and left of the stomach - Structurally similar to lymph node except it serves as a filter for blood instead of lymph - Primary function is to remove worn-out blood cells from circulation - Most important immune function = filtering pathogens from the blood and their subsequent phagocytosis by resident macrophages

Molecular Shape and Size on Antigenicity

• To initiate an immune response - substance must be large enough to be seen by surveillance cells • Molecular Weight (MW) of <1000 - not complete antigens • MW 1000-10,000 - weak • Complex macromolecules of at least 100,000 MW are most immunogenic (dominated by large proteins) • Size alone is not sufficient for antigenicity Ex) Glycogen (polymer of glucose) - MW >100,000 and is not normally antigenic Ex) Insulin (protein) - MW 6000 and can be antigenic • Antigens have many Antigenic Determinants (Epitopes)* - small molecular group recognized by lymphocytes - Provides the primary signal that the molecule is foreign** - Shape of determinant fits like a key to the receptor lock of the lymphocyte Ex) certain amino acids accessible at the surface of proteins or carbohydrate side chains protruding from a protein receptor Ex of multiple/mosaic antigens - bacterial cell wall, membrane, flagellar, capsular, toxin antigens, viruses • Haptens* - small foreign molecules that consist only of a determinant group and too small by themselves to elicit an immune response** - Carrier group contributes to the size of the complex and enhances the orientation of the antigen, while the hapten serves as the epitope Ex) vaccine antigens, drugs, metals, variety of chemicals - Also develop immunogenicity in the body by combing with large carrier molecules i.e. serum proteins

Nonspecific Mediators of Inflammation and Immunity

• Tumor necrosis factor (TNF) - substance from macrophages, lymphocytes, and other cells - Increases chemotaxis and phagocytosis and stimulates other cells to secrete inflammatory cytokines - Triggers fever (is an endogenous pyrogen) and stimulates blood coagulation - Potential to damage tissues when produced in excess • Interferon alpha and Interferon beta - produced by leukocytes and fibroblasts, inhibit virus replication and cell division and increase action of certain lymphocytes that kill other cells • Interleukin - group of small peptides originally isolated from leukocytes - Currently more than 50 known interleukins - Other cells besides leukocytes can synthesize them - Variety of biological activities > Interleukin-1 (IL-1) - product of macrophages and epithelial cells - Same biological activities as TNF (inducing fever, activating certain WBCs) > Interleukin-6 - secreted by macrophages, lymphocytes, fibroblasts - Primary effects are to stimulate the growth of B cells - Increase synthesis of liver proteins i.e. C-Reactive Protein - Interleukins - stimulate B cell differentiation** • Various chemokines - chemokines are cytokines that stimulate the movement and migration of WBCs (chemotactic factors) - Included are complement C5a, interleukin-8, and platelet-activating factor

How do WBCs carry out recognition and surveillance?

• WBCs are motile, migratory cells that move about the tissues and body compartments in search of foreign matter that may have gotten through the 1st line of defense • Pattern recognition receptors (PRRs)* - molecules on cell membranes that are "feelers" for sensing pathogens - Several PRRs are involved in recognition including kinases, lectins, and mannose-type molecules - Best understood PRR are Toll-Like Receptors (TLRs)* - reside within the membranes of early responders i.e. Phagocytes • PRRs and TLRs can recognize and interact with molecules on the surface of many pathogens called = Pathogen-Associated Molecular Patterns (PAMPs)* - molecules shared by many microorganisms that act like "red flags" that signal WBCs involved in innate immunity - Detection of PAMPs on pathogens by PRRs and TLRs provides early alert of invasion + triggers reactions that help to control pathogens before they can invade further • This type of recognition is NOT specific or selective for a single type of microbe = NON-specific, innate immunity (should not be confused w/ specific acquired immunity from 3rd line of defense) PAMPs Ex) Peptidoglycan, Lioteichoic Acid, Lipopolysaccharide from bacterial cell walls, double-stranded RNA found in some viruses, zymosan from fungal cell walls, bacterial flagellin

Characteristics of WBCs

• WBCs leave the blood vessels and enter tissues, they adhere to the inner walls of the smaller blood vessels i.e. capillaries and venules - migrate out of the blood into the tissue by Diapedesis* • Diapedesis (transmigration) - migration of intact blood cells between endothelial cells and a blood vessel i.e. venule - Aided by several related characteristics of WBCs i.e. are actively motile and readily change shape - Migration is assisted by the nature of endothelial cells lining venules - Venules contain complex adhesive receptors that develop increased "stickiness" under the influence of inflammatory mediators - Causes WBCs to adhere or marginate at the endothelial cells - can readily crawl into the extracellular spaces • Chemotaxis* - Tendency of cells to migrate in response to a specific chemical stimulus released at a site of injury or infection - Cells swarm from many compartments to the site of infection and remain there to perform general functions i.e. phagocytosis, repair, specific immune reactions = essential for the sort of intercommunication and deployment of cells required for most immune reactions

Characteristics of Antiviral Interferon

• When virus binds to the receptors on a host cell, signal is sent to the nucleus that directs the cell to synthesize interferon • After transcription and translation of the interferon gene, newly synthesize interferon molecules are rapidly secreted by the cell into the extracellular space, and bind to other host cells • Binding of interferon to 2nd cell induces production of another class of proteins that inhibit viral multiplication by preventing the translation of viral proteins • Interferon is not virus-specific • Synthesis in response to 1 type of virus will also protect against other types • Protein is an inhibitor of viruses • It has been valuable treatment for a # of viral infections • Important immune regulatory cytokines that activate or instruct the development of WBCs Ex) Interferon alpha produced by T lymphocytes activates a subset of cells called Natural Killer (NK) cells • 1 type of interferon beta plays a role in the maturation of B and T lymphocytes and in inflammation • Interferon gamma inhibits cancer cells, stimulates B lymphocytes, activates macrophages, and enhances the effectiveness of phagocytosis

Origin, Composition, and Functions of Blood: Whole Blood, Plasma, Serum

• Whole blood: substances that course through arteries, veins, capillaries; liquid connective tissue with blood cells (formed elements) suspended in plasma • Can be seen when tube of unclotted blood is allowed to sit or is spun in a centrifuge = cells' density causes them to settle into bottom of tube - Plasma will be clear, yellowish fluid at the top • Plasma - contains 100s of different chemicals produced by the liver, WBCs, endocrine glands, nervous system, and absorbed from the digestive tract - 92% water; remainder consists of proteins (albumin, globulins, antibodies), immunochemicals, fibrinogen, clotting factors, hormones, nutrients, ions and electrolytes, dissolved gases (O2, CO2), waste products (urea) = substances support the normal physiological functions of nutrition, development, protection, homeostasis, and immunity • Serum: clear, fluid from clotted blood that lacks clotting proteins* - Often used in immune testing and therapy

Host Defenses: Innate Immunity and Adaptive Immunity

▪ Innate immunity, natural defenses: present at birth, provide NONSPECIFIC resistance to infection • First line of defense - Physical barriers - Chemical barriers - Genetic barriers • Second line of defense - Inflammatory response - Interferons - Phagocytosis - Complement ▪ Adaptive immunities: SPECIFIC, must be acquired • Third line of defense - B and T lymphocytes, antibodies, cytotoxicity

Specific B-Cell Receptor: Immunoglobulin = Antibodies

▪ Plasma cells secrete immunoglobulins called antibodies* ▪ Immunoglobulins - large glycoproteins that serve as specific receptors of B cells and as antibodies • Composed of 4 polypeptide chains in a Y-shaped arrangement: - 2 identical heavy chains (H)** - 2 identical light chains (L)** • Wide range of variable antigen binding sites at the end of the forks formed by these chains is due to variable (V) regions • The constant (C) regions do not vary greatly • Each light chain binds to a heavy chain and 2 heavy chains bind to each other with disulfide bonds, creating a symmetrical (Y) shaped arrangement*

Defense Mechanisms of the Host

▪ To protect the body against pathogens, the immune system relies on a multilevel network of physical barriers, immunologically active cells, and a variety of chemicals • First line of defense, nonspecific - any barrier that blocks invasion at the portal of entry - Not considered a true immunity response because it does not involve recognition of a specific foreign substance and is very general. • Second line of defense, nonspecific - protective cells and fluids; inflammation and phagocytosis - Acts rapidly at both local and systemic levels once the 1st line has been circumvented • Third line of defense, specific - adaptive and acquired with exposure to foreign substance - produces protective antibodies against microbes and creates memory cells if encountered again • The lines of defense do not work separately, most overlap and are redundant in some of their effects