Chapter 26

phagocyte

a cell that engulfs foreign particles, and can ingest, kill, and digest most pathogens

plasma cell

a differentiated B cell that produces soluble antibodies

Major Histocompatibility Complex (MHC)

a genetic region that encodes several proteins important for antigen processing and presentation. MHC I proteins are expressed on all cells. MHC II proteins are expressed only on antigen-presenting cells

macrophages

a large leukocyte found in tissues that has phagocytic and antigen-presenting capabilities

granulocyte

a leukocyte derived from a myeloid precursor that contains cytoplasmic granules consisting of toxins or enzymes that are released to destroy target cells.

neutrophil

a leukocyte exhibiting phagocytic properties, a granular cytoplasm (granulocyte), and a multilobed nucleus; also called polymorphonuclear leukocyte or PMN

B cell

a lymphocyte that has immunoglobulin surface receptors, produces immunoglobulin, and may present antigens to T cells

inflammation

a nonspecific reaction to noxious stimuli such as toxins and pathogens, characterized by redness (erythema), swelling (edema), pain, and heat (fever), usually localized at the site of infection

leukocyte

a nucleated cell in blood; also called a white blood cell

Mucosa-associated lymphoid tissue (MALT)

a part of the lymphatic system that interacts with antigens and microorganisms that enter the body through mucous membranes, including those of the gut, the genitourinary tract, and bronchial tissues

dendritic cell

a phagocytic antigen-presenting cell found in various body tissues; transports antigen to secondary lymphoid organs

complement system

a series of proteins that react sequentially with antibody-antigen complexes, mannose-binding lectin, or alternative activation pathway proteins to amplify or potentiate target cell destruction

cytokine

a soluble protein produced by a leukocyte or damaged body cell; modulates an immune response

Chemokine

a soluble protein that recruits immune cells to an injury site; a type of cytokine

natural killer cells (NK cells)

a specialized lymphocyte that recognizes and destroys infected host cells or cancer cells in a nonspecific manner

lymphocytes

a subset of nucleated cells in blood involved in the adaptive immune response

What other factors may control the outcome of an infectious disease?

a. Adaptive immunity b. Acquired ability to recognize a particular pathogen or its products c. Dependent on previous exposure to pathogens or its products d. Directed toward an individual molecular component of the pathogen e. Host hygiene f. Innate immunity g. Normal host microbiota

Describe the circulation of a leukocyte from the blood to the lymph and back to the blood.

a. Blood is pumped through arteries and capillaries and returns from the body through veins. b. In capillary beds, leukocytes and solutes pass from blood into the lymphatic system. i. Lymph nodes contain high concentrations of lymphocytes and phagocytes. c. Lymph versus blood i. Lymph 1. Made up of +/- lymphocytes 2. Thicker 3. Movement via skeletal muscle 4. Travels through vessels with valves 5. Nodes with T cells a. Swollen with infection (spread of cancer, etc.) ii. Blood 1. Serum 2. RBC/WBCs 3. Movement via the heart 4. Travels through veins with valves

Describe the relative importance of innate immunity compared to adaptive immunity. Is one more important than the other? Can we survive in a normal environment without immunity?

a. Both are equally as important immune responses. The two go hand-in-hand. The innate immune response can react to pathogens much quicker than adaptive immunity, but more types of pathogens can get past the innate immunity. We need both to work together to stay healthy and alive. b. No, we cannot. Too many pathogens would easily kill us.

What are complement and the complement pathway?

a. Complement—serum protein that binds in a cascade and lyses cell; circulates, waiting for a response to a pathogen b. Complement pathway (complement cascade)—series of binding complement proteins to cell; end with opsonization, direct attack, and recruitment of phagocytes.

Describe host tissue specificity for pathogens?

a. Different pathogens invade different tissues. i. Binding receptors must match up b. Routes of infection are crucial (e.g., tetanus is in wounds, while Salmonella is ingested, not vice versa).

Describe the potential problems that would arise if a person had an acquired inability to phagocytose pathogens. Could the person survive in a normal environment such as a college campus? What defects in the phagocyte might cause lack of phagocytosis? Explain.

a. If a person couldn't phagocytize pathogens, then he would not be able to present the antigens of the pathogens to T cells or B cells to create antibodies that would destroy the pathogen. Pathogens wouldn't be able to be destroyed through phagocytosis, so pathogens would just keep growing and growing, destroying the body b. This person would not be able to survive in a normal environment; only hopes for survival is a sterile bubble c. The phagocyte needs antibodies to present the pathogen to the phagocyte, or it needs complement proteins to be able to phagocytize the pathogen. If the receptors for the antibodies or receptors for the complement proteins are not functioning, then phagocytosis would not be able to be achieved.

Describe the inflammation reaction. What are some causes of inflammation?

a. Inflammation is a nonspecific reaction to noxious stimuli. i. Steps 1. Damaged cells release histamines, prostaglandins, and leukotrienes 2. Cause vasodilation 3. More blood (phagocytes, O2, and nutrients) delivered to injury a. Proteins called cytokines and chemokines draw white blood cells to a site of inflammation. 4. Direct effect on local capillaries—leakier; fluid leaves to cause swelling b. Effective inflammatory response isolates and limits tissue damage, destroying damaged cells and pathogens. c. Causes i. local infection ii. innate immune responses iii. adaptive immune responses iv. injury to tissues by trauma, toxins, heat, or other damage

What major class of immune cells mediates an innate immune response? What additional type of immune cells is required for an adaptive immune response?

a. Innate—macrophages, dendritic cells, neutrophils, natural killer cells (phagocytes) b. Adaptive—B and T (lymphocytes)

Under what conditions are interferons produced, and how do they limit the transmission of viruses from one host cell to another?

a. Interferons are produced in large amounts by cells infected with viruses of low virulence b. Interferons serve as a warning system and prevent viral replication by stimulating the production of antiviral proteins in uninfected cells once they receive the interferon signal from infected cells.

Identify the major symptoms of localized inflammation and of septic shock.

a. Local inflammation -- redness, swelling, pain, and heat localized at site of infection b. Septic shock -- an inflammatory response that spreads inflammatory cells and mediators through the entire circulatory and lymphatic systems i. Widespread (systemic) inflammation can lead to shock as the increased vascular permeability decreases a host's blood pressure, which can cause damage to multiple organs at the same time. ii. low blood pressure, pale and cool arms and legs, chills, difficulty breathing, decreased urine output

What are examples of lymphoid tissue?

a. Lymph nodes b. Spleen c. Tonsils d. Adenoids e. Thymus

What are MHCs and why are they important?

a. MHC—major histocompatibility complex i. Antigens found on the surface of nucleated cells ii. Antigens cause an immune response iii. Blood does not have MHC because RBC have no nuclei iv. RBC antigens are A, B, or RH antigens b. Importance—Allow body to recognize itself, so we don't kill off our own, healthy cells

Identify physical and chemical barriers to pathogens. How might these barriers be compromised?

a. Mucosal membranes are coated with a thick layer of mucus. i. Thick layer of mucus to suspend and move microorganisms outside the body ii. Contains lysozyme b. Stomach acid inhibits bacterial growth. c. Skin is salty and acidic, limiting bacterial growth. d. Wounds especially compromise physical barriers to pathogens

Although technically not part of the immune system, nonpathogenic normal microbiota plays a major role in preventing disease. Describe this role.

a. Normal Microbiota helps host resist pathogens, particularly on the skin and in the gut by means of competitive exclusion. The normal microbiota out-competes most pathogens for nutrients, not allowing the pathogenic organisms to grow and thrive.

What is opsonization, and how does opsonization help fight bacterial infections?

a. Opsonization—coating of pathogens with antimicrobial host proteins (antibodies or C3b), resulting in enhanced phagocytosis of target cells i. a step within phagocytosis and complement systems b. It neutralizes pathogens and makes them much more likely to be identified, engulfed, and destroyed by phagocytes

What term is used to describe the unique molecules found on the surface of different pathogens?

a. Pathogen-associated molecular patterns (PAMP) i. Pathogens have structures and molecules not found in or on host cells (e.g., peptiglycan, flagellin, dsRNA).

Describe the process of phagocytosis. What types of cells are phagocytic?

a. Phagocytes will engulf pathogens upon recognition of PAMPs by their TLRs (toll-like receptors) b. When engulfed, the bacteria will be held in a membrane bound vesicle called the phagosome. c. The phagocytic host cell will fuse lysosomes, making a phagolysosome. d. Phagocytes also produce toxic reactive oxygen intermediates to kill the bacteria within a phagolysosome. i. Some pathogens can survive the phagolysosome. 1. Mycobacteria tuberculosis 2. Streptococcus pyogenes produces leukocidins, which kill white blood cells. Dead white blood cells are found in pus. ii. Lastly, some pathogens contain a capsule, which makes it difficult for the phagocyte to engulf them.

Where do all blood cells originate? What determines what they differentiate into?

a. STEM cells located in the red bone marrow of long bones b. Differentiation occurs based upon which lymphoid organ the cells mature in i. Cytokines influence the development of stem cells. c. Ex. Leukocytes (nucleated WBCs) i. Lymphocytes are specialized leukocytes involved exclusively in adaptive immune response. 1. two types of lymphocytes a. B cells: originate and mature in bone marrow from plasma cells i. Make antibodies b. T cells: originate in bone marrow, but mature in thymus. ii. Bone marrow and thymus are primary lymphoid organs.

Describe several reasons why phagocytes are not always effective at removing pathogens from the body.

a. Some pathogens can survive the phagolysosome. i. Mycobacteria tuberculosis ii. Streptococcus pyogenes produces leukocidins, which kill white blood cells. Dead white blood cells are found in pus. b. Lastly, some pathogens contain a capsule, which makes it difficult for the phagocyte to engulf them.

Identify and compare the targets and the recognition mechanisms used by T-cytotoxic cells and NK cells.

a. T-cytotoxic cells i. Targets—infected cells ii. Recognition mechanisms—in cells that have been infected by viruses or other intracellular pathogens, MHC I proteins display peptides derived from the infectious agent (pathogen). This is the signal to the T-cytotoxic cells b. NK cells - cytotoxic lymphocytes i. Targets—cancerous or virus-infected host ii. Recognition mechanisms—recognizes cells that do not display Major Histocompatibility Complex I (MHC I) proteins, as all normal host cells should have MHC I. iii. If a cell lacks MHC I and displays a stress protein, an NK cell will activate to destroy the target, which is likely a virally infected or cancerous host cell.

fever

an increase in body temperature resulting from infection or the presence of toxins in the body

phagosome

an intracytoplasmic vacuole containing engulfed materials, especially pathogens or foreign particles

Antibody-dependent cell-mediated cytotoxicity

antibodies attached to target cell cause destruction by macrophages, eosinophils, and NK cells

T cell receptor (TCR)

antigen receptor on the surface of a T cell

immunoglobulins

bind with specific antigens in the antigen-antibody response

hematopoietic stem cell

cell in the bone marrow that gives rise to all types of blood cells

Antigen-presenting cells (APCs)

cells such as B cells, macrophages, and dendritic cells that can present exogenous antigens to naive or memory T cells, activating them

interferons

cytokine proteins produced by virus-infected cells that induce signal transduction in nearby cells, resulting in transcription of antiviral genes and expression of antiviral proteins

Hematopoiesis

formation of blood cells

immune memory

immune system remembers invaders it has destroyed before and kills them quickly the second time

T-cell

o a lymphocyte that interacts with antigens through a T cell receptor for antigen o T cells are divided into functional subsets including Tc (T-cytotoxic) cells and Th (T-helper) cells. Th cells are further subdivided into Th1 (inflammatory) cells and Th2 cells, which aid B cells in antibody formation

Antibody

o a soluble protein produced by B cells and plasma cells that interacts with antigen; also called immunoglobulin - serum proteins produced by plasma cells in response to antigens - antibody levels : titre

Adaptive immunity

o the acquired ability to recognize and destroy a particular pathogen or its products, dependent on previous exposure to the pathogen or its products - specific - antigen presenting - cell-mediated immunity · T cells - Humoral immunity · B cells · Antibodies

lymph nodes

organs that contain lymphocytes and phagocytes arranged to encounter microorganisms and antigens as they travel through the lymphatic circulation

invasion

the ability of a pathogen to enter into host cells or tissues, spread, and cause disease

immunity

the ability of an organism to resist a particular infection or toxin by the action of specific antibodies or sensitized white blood cells.

specificity

the ability of the immune response to interact with particular antigens

Antigen

A protein that, when introduced in the blood, triggers the production of an antibody

opsonization

the deposition of antibody or complement protein on the surface of a pathogen or other antigen that results in enhanced phagocytosis

monocyte

Circulating phagocyte in the blood that contains many lysosomes and can differentiate into a macrophage or dendritic cell - Antigen presenting

plasma

the liquid portion of the blood containing proteins and other solutes

serum

the liquid portion of the blood with clotting proteins removed

innate immunity

the noninducible ability to recognize and destroy an individual pathogen or its products that does not rely on previous exposure to a pathogen or its products - non-specific - first line of defense (skin) - phagocytosis (dendritic cells) - inflammation - complement system (serum) - natural killer cells · levels do NOT go up · born with set amount

phagocytosis

the process of engulfing and killing foreign particles and cells - chemotaxis attracts à pseudopods attach - adherence à opsonization - ingestion into the phagosome via endocytosis - + lysozyme = phagolysozome (10-30 min.) -exocytosis/elimination · this is where antigen presenting takes plac

eosinophil

Leukocyte that is active in the presence of parasites and malaria

B cell receptor (BCR)

Molecule on the surface of a B cell that binds to a specific antigen.

mast cell

tissue cells adjoining blood vessels throughout the body that contain granules with inflammatory mediators like histamine (vasodilator)

stem cell

unspecialized cell that can give rise to one or more types of specialized cells

epitope

Small, accessible portion of an antigen that can be recognized.

Basophil

white blood cell containing granules that stain blue; associated with release of histamine and heparin