Microbiology Exam 1

Type I Interferons

-Human type I Interferons comprise a large group of IFN proteins. The name was meant to suggest "interfering with a virion", which is a viral particle. -There are two very important anti-viral type I interferons: Interferon-α and Interferon-β The IFN-α proteins come in 13 subtypes that are called IFNA1, IFNA2 and so on... -There is but one functionally active IFN-β. -The most potent stimulus for IFNs are viral nucleic acids - as detected by pattern recognition receptors. (Double-stranded RNA, Single-stranded RNA, and unmethylated CpG DNA) -Homologous molecules to IFN-α/β are found in many species, including most mammals, and some have been identified in birds, reptiles, amphibians and fish species.

Biological Events of Inflammation

-Increased blood supply: increases delivery of proteins and leukocytes. -Increased permeability: increases tissue entry of proteins and leukocytes. -Increased migration: increases entry of leukocytes into tissue -Increased tissue activation= interactions between leukocytes, endothelial cells, extracellular matrix components, cytokines, chemokines, hormones & antigen/pathogen.

How does soluble antigen activate B cells?

-Involves crosslinking of immunoglobulin receptor (primarily IgM) -Typically involves antigens with long repeating epitopes (e.g., LPS), but not proteins -Primarily results in the production of IgM A B cell's phenotype and function changes. In response to antigen, their proliferation increases, increased expression of B7-1/B7-2, of cytokine receptors (IL-2, IL-4), and of expression of CCR7 (a chemokine).

2 major functions of monoctyes and (as they differentiate) macrophages

1. Act as professional phagocytes to take up/remove particulate antigens. 2. Act as antigen-presenting cells (APC) to take up, process, and present antigenic peptides to T cells.

Controlling leukocyte entry into peripheral sites

1. Blood flow (shear force): Post-capillary venules have less shear force and thin vessel wall. 2. Electrostatic interactions: Net (-) charge on endothelia and inflammatory cells There is repulsion under physiological conditions, but electrostatic grasping can occur after injury/infection due to changes in charge distribution

Reactive Endothelium

1. TNF-α and IL-1 increases the expression of selectins, which bind to ligands and are responsible for rolling. 2. Integrin on leukocytes are expressed as a result of chemokine/receptor complex binding. Shifts from low affinity to high affinity binding, and are clustered. 3. Expression of integrin ligands on the endothelium are increased as a result of TNF-α and IL-1 After Step 3, Cells Are Stably Adhered 4. Leukocytes transmigrate through the endothelium and chemokines act on the cell to draw the cell toward the site of infection.

5 basic steps in antigen processing

1. Tagging the antigen for destruction 2. Proteolysis of antigen (broken down) 3. Peptide delivery to MHC molecules 4. Peptide binding to MHC molecules 5. Display of MHC-peptide complexes on APC surface

MHCII processing of EXOGENOUS antigen

1. Uptake extracellular proteins into vesicular compartments of APC 2. Processing of internalized proteins in endosomal/lysomal vesicles 3. biosynthesis and transport of MHCI Ito endosomes 4. association of processed peptides with MHCII molecules in vesicles 5. expression of peptide-MHCII complexes on cell surface

MHCI processing of ENDOGENOUS antigen

1. production of proteins in the cytosol 2. proteolytic degradation of proteins 3. transport of peptide from cytosol to the ER 4. assembly of peptide-class I complexes in ER 5. Surface expression of peptide-class I complexes

First true "test" of a vaccine

1796, Jenner tested his theory by inoculating James Phipps, 8 years old, with material from the cowpox blisters of the hand of Sarah Nelmes, a milkmaid who had caught cowpox from a cow named Blossom. (The VACCINE) Jenner inoculated Phipps with cowpox pus in both arms on one day, by scraping the pus from Nelmes' blisters onto a piece of wood then transferring this to Phipps' lacerated arms. This produced mild cowpox with fever and some uneasiness. (The TEST) Later, he injected Phipps with liquid from sores from a patient with a mild case of smallpox that would normally cause disease. No disease followed. (Memory) Jenner reported that later the boy was again challenged with variolacious material and again showed no sign of infection.

MHC Restriction

Allows individual T cells to recognize foreign Ag displayed on the surface of an individual APC to distinguish between self and non self In the thymus, the organ where T cells mature, T cells which are specific for foreign Ag + MHC (POSITIVE selection) bind with low avidity to self peptide-MHC complexes survive and TCRs that bind with high avidity die (NEGATIVE selection). Prevents destruction of self tissue (autoimmunity).

Non-professional APCs

Almost all nucleated cells can become an APC after infection and activation. "Non-professional" APCs do not constitutively express MHC II, which is required for naïve T cell activation (all have MHC I for self-recognition). They express MHC only upon stimulation of the cell by certain cytokines such as INF-g.

Antigen

An antigen (Ag) is any substance that can be specifically bound by a cell of the adaptive immune system

Allergen

An antigen that causes an immediate hypersensitivity (allergic) reaction.

Immunogen

An antigen that ellicits an immune response.

Tolergoen

An antigen that induces immunological tolerance or immune non-responsiveness.

Eradication of Smallpox

Announced by the WHO in 1980. Today, it is the only completely eradicated human infectious disease.

Exogenous antigen

Antigen directly entering the body from the environment. Ex. Inhaled antigen (e.g. cat hairs, pollen), ingested antigen (e.g. shellfish protein, peanuts), injected antigen (e.g. splinter, injected vaccine). These are antigens presented by APCs to CD4+ Tcells. B cells and antibodies play an important role.

Steps in CTL-mediated lysis of target cells

Antigen recognition and conjugate formation is the first step. CTL is activated. Granules are exocytosed which enter target cell cytoplasm through perforin-dependent mechanisms, activating apoptosis pathway. The CTL detaches, and the target cell dies. This whole process happens within minutes.

Endogenous antigen

Antigens generated within the cells of the body as a result of normal metabolism or viral infection. Proteins encoded for by genes of viruses and abberant proteins encoded for by mutated genes (e.g. cancer cells). These are antigens presented by APCs to CD8+ T cells. NK cells play an important role.

Recruitment of leukocytes

At sites of infection, macrophages that have encountered microbes produce cytokines (such as TNF and IL-1) that activate the endothelial cells of nearby venules to produce selectins, ligands for integrins, and chemokines. Selectins mediate weak tethering and rolling of blood leukocytes on the endothelium; integrins mediate firm adhesion of neutrophils, and chemokines increase the affinity of neutrophil integrins and stimulate the migration of the cells through the endothelium to the site of infection. Blood neutrophils, monocytes, and activated T lymphocytes use essentially the same mechanisms to migrate to sites of infection.

Antigen recognition during an adaptive immune response

B cells recognize by membrane bound immunoglobulin. T Cell requires APC, MHC, and antigen. The CD3 ligand is what actually phosphorylates and creates a response.

Professional APCs

B cells, macrophages, and dendritic cells. - They constitutively express high(er) levels of MHCII and costimulatory molecules, and are efficient inducers of T cell responses.

Humoral vs. cell-mediated adaptive immunity

B lymphocytes secrete antibodies that prevent infections and eliminate extracellular microbes. In cell-mediated immunity, helper T lymphocytes activate macrophages to kill phagocytosed microbes or cytotoxic T lymphocytes (CTLs) directly destroying infected cells.

APC co-stimulatory molecules

B71/B72- Ligates (activates) CD28 or CTLA4 on a T cell and sends important signals for cell functions.

How do intracellular pathogens try to avoid the immune system?

Block MHC synthesis, block transport mechanisms of HSV, interfere with CTL receptors

T cell Co-stimulatory molecules

CD28 - Activates T cell induces proliferation (clonal expansion). CTLA4 - negative signal, stops clonal expansion. It can competitively inhibit CD28 binding to CD28. When bound to B7, will actively block signals from the TCR and from CD28.

CD4+ T cells

CD4+ T cells are MHC II restricted and recognize extracellular and intravesicular pathogens (exogenous). They produce INF-y to activate macrophages, and produce cytokines to provide costimulation for CD8+ T cell activation, and cytokines to enhance activity of APCs.

CD8+ T cells

CD8+ T cells are MHC I restricted and recognize cytosolic (endogenous) proteins such as virus and tumor cells.

Cytoxic T Cells (CTLs) and antigen

CTLs recognize antigens on infected cells and kill these cells (especially viruses). Their characteristic surface marker is CD8. They secrete perforins, granzymes, and cytokines.

Macrophages

Cells of the INNATE immune system, their main function is phagocytosis of and intracellular killing of microorganisms. They are capable of extracellular killing of infected or altered self target cells and contribute to tissue repair. They can act as antigen-presenting cells, which are required for the induction of specific immune responses. They express both MHCI and MCHII

Natural Killer (NK) Cells

Cells of the INNATE immune system, they, and lymphokine activated killer (LAK) cells, can nonspecifically kill virus infected and tumor cells. They can produce cytokines (IFN-Y) for macrophages early in infection. When activated, they are degranulated=killing. They are important in nonspecific immunity and are the first line of defense to viral infections and tumor surveillance.

Eosinophils

Cells of the INNATE immune system. Eosinophils have proteins in granules that are effective in killing certain parasites. Involved in inflammatory and allergic responses (particularly in the skin and airway). Release histamine. They induce their function by degranulating and releasing: eosinophil catitonic protein, major basic protein, eosinophil peroxidase, ROS/NO intermediates.

What is the principal cell connecting the innate and adaptive immune systems

Dendritic cells

Microglia

Differentiated macrophages of the CNS

Osteoclasts

Differentiated macrophages of the bone

Kupffner Cells

Differentiated macrophages of the liver

alveolar macrophages

Differentiated macrophages of the lung

Deaths due to smallpox

During the 20th century, it is estimated that smallpox was responsible for 300-500 million deaths. As recently as 1967, the World Health Organization (WHO) estimated that 15 million people contracted the disease and that two million died in that year.

How do cells of the innate immune response detect antigen?

Extracellular surface TLRs and intracellular endosomal TLRs

How do Fas:FasL interactions eradicate cells with INTRACELLULAR pathogens

Fas receptor trimerization activates the death domain Fas Associated Death Domain (FADD), leads to signaling cascades that activate caspase 8, which can activate Bid and Caspase 3.

Innate Immunity: Chemical Barriers

Fatty acids in sweat, lysozyme and phospholipase found in tears/saliva/snot, low pH of sweat and gastric secretions, defensins (low molecular weight proteins) found in the lung and gastrointestinal, surfactants in the lung.

Which interleukins drive the development of helper T cells?

IL-12 - drives development of Th1 cells IL-4 - drives development of Th2 cells

Antibody Isotypes After Exposure to a Microbial Infection...

IgM shown in the first few days, and it's usually T cell INDEPENDENT. IgG shown 10-14 days after infection and is T cell DEPENDENT.

Innate Immunity: Physical Barriers

Include epithelial and mucosal surfaces. Skin is the FIRST line of defense. Cilia and mucus protect GI tract and respiratory passages from infection. The flushing action of tears and saliva helps prevent infection of the eyes and mouth.

Isotype switching

Isotype switching of B cells is dependent on interactions with BOTH T cells, and cytokines. An activated IgM B cell, will mature into and IgM B cell that can assist in complement. A B cell with IFN-y will mature into IgG. A B cell with IL-4 will mature into IgE. Finally, other cytokines such as TGF-B will lead to a mature B cell that expresses IgA.

How does the immune system kill an intracellular pathogen?

It kills the entire host cell with the pathogen too

Properties of MHC genes

Known also as HLA (human leukocyte antigen) in humans. MHC genes are highly polymorphic w/ hundreds of alleles in humans with approximately 1013 combinations (most polymorphic genes in the human genome). Leads to transplant difficulties. MHC alleles are concomitantly expressed.

Where do mature B cells take residence?

Long lived antibody producing plasma cells are in the bone marrow and memory B cells take up residence in lymph nodes.

Defensins

Low molecular weight proteins part of chemical innate immunity found in the lung and GI tract, and have antimicrobial activity.

MHC

MHC is essential for antigen presentation to T cells T cells constantly survey for foreign antigens. Self MHC + foreign Ag = T cell response Self MHC + self Ag = No T cell response. MHC is expressed or it's expression can be induced on almost every nucleated cell in the body. Viruses can infect virtually any nucleated cell so MHC I functions to alert the CD8+ T cells. MHC expression tells the immune system that the cell is a "self" cell. MHC is a KEY factor in determining tissue matching for transplant donors and recipients.

MHC-peptide interactions

MHC molecules have a broad specificity for peptides, i.e. many different peptides can bind within the MHC binding cleft. Peptides associated with MHC have a slow on and slow off rate. MHC molecules do not discriminate from self and foreign peptides. The MHC haplotype of an individual determines which peptides bind and how peptides bind.

How does granzyme B induce apoptosis

Method One: 1. By activating caspases (specifically caspase 3) 2. Caspase 3 activation will lead to Caspase Activated DNAse (CAD) 3. CAD causes DNA fragmentation and, thus, apoptosis. Granzyme B can also directly activate CAD Method Two: 1. By activating BH3-interacting domain death agonist (BID). BID destroys the integrity of the mitochondrial outer membrane (induces formation of BAD/BAX channel. Pro-apoptotic factors are released from the mitochondrial membrane. Cytochrome C will activate caspase 9 and endonuclease G (ENDOG) which cleaves DNA.

Method of phagocytosis

Microbes may be ingested by different membrane receptors of phagocytes; some directly bind microbes, and others bind opsonized microbes. (Note that the Mac-1 integrin binds microbes opsonized with complement proteins). The microbes are internalized into phagosomes, which fuse with lysosomes to form phagolysosomes, where the microbes are killed by reactive oxygen species (ROS), nitrogen intermediates such as nitric oxide (NO) and proteolytic enzymes.

Maturation of monoctyes

Mononuclear phagocytes develop in the bone marrow, circulate in the blood as monocytes, and are resident in all tissues of the body as macrophages. They may differentiate into specialized forms (note different names!) in particular tissues.

Important non-specific receptors on innate immune cells

N-formyl-methionyl-receptor, mannose receptor, scavenger receptor all aid in phagocytosis. TLR's recognize antigen.

Naive B cells

Naïve B cells express antibody on it's surface, but it's secured to its surface it won't circulate (because it's never seen the antigen, whether exposed or vaccinated). Therefore, it CANNOT secrete antibodies.

Innate immunity: biological barriers

Normal flora of the skin and in the gastrointestinal tract can prevent the colonization of pathogenic bacteria by secreting toxic substances or by competing with pathogenic bacteria for nutrients or attachment to cell surfaces.

T and B cell interaction

Occurs in the lymph node. B cells migrate to the edge of the follicle, and into the T zone. T cells migrate to the edge of the T zone (to interact). The interaction leads to B cell Ig secretion, and isotype switching, and requires CD40 co-stimulation as well as cytokines. Then, a reaction in the germinal center of the lymph node causes B cells to undergo affinity maturation, become long-lived plasma cells, or memory cells.

What is the function of the antibody IgG?

Opinsization and phagocytosis of microbes (through phagocytes), and antibody-dependent cellular cytotoxicity (through NK cells).

Lymphocyte Activation

Part of ADAPTIVE immunity. Lymphocytes mature in the bone marrow (B cells) and thymus (T cells), and enter secondary (peripheral) lymphoid organs as "naive" lymphocytes. Antigens are captured from their site of entry by dendritic cells (APCs) and concentrated in lymph nodes, where they activate naive lymphocytes that migrate to the nodes through blood vessels. Effector and memory T cells develop in the nodes and enter the circulation, from which they may migrate to peripheral tissues. Antibodies are produced in lymphoid organs and enter the circulation, from which they may locate antigens at any site. Memory cells also enter the circulation and may reside in lymphoid organs and other tissues.

Kinetics of T cell activation

Part of adaptive immunity. 1. Adhesion to APC or target cell. 2. Signal one: Ag specific activation and signal transduction. 3. Co-stimulation by B7.

B cells

Professional APCs. Internalize Ag via Ig receptor (therefore restricted to single antigenic specificities) They have high constitutive levels of MHC II (highest of the three). They are efficient activators of CD4+ T cells. They become activated by helper T cells, where they can secrete antibodies, isotype switch, and become memory B cells.

Professional phagocytes

Professional phagocytes include: neutrophils, monocytes, macrophages. Serve to protect the host by recognizing, taking up, and killing invading microbes.

Cytokines

Proteins produced by many different cell types that mediate inflammatory and immune reactions. Cytokines are principal mediators of communication between cells of the immune response. Termed interleukins. Critical for activating a cell, turning on proteins that regulate apoptosis, trafficking cells to an infection. Ex. TNF (tumor necrosis factor), IL-1, IL-12

Helper T cell lymphocytes and antigen

Recognize antigens on the surfaces of APCs (in the context of MHC) and secrete cytokines, which stimulate different mechanisms of immunity and inflammation. TH1 (helper T 1) activate macrophages. TH2 aids B lymphocytes in proliferation and antibody secretion.

B lymphocytes and antigen

Recognize soluble antigens and develop into antibody-secreting cells.

Regulatory T cells and antigen

Regulatory T cells suppress and prevent immune response, e.g. to self antigens.

Desquamation

Shedding of the outer keratinoctyes. Helps remove bacteria and other infectious agents. A part of innate immunity.

Smallpox

Smallpox is believed to have appeared around sometime before 4,000 BC. The earliest evidence of skin lesions resembling those of smallpox is found on faces of mummies from the time of the 18th and 20th Egyptian Dynasties (1570-1085 BC). The mummified head of the Egyptian pharaoh Ramses V (died 1156 BC) bears evidence of the disease Between 20 and 60% of all those infected—and over 80% of infected children—died from the disease. Those who survived, were left permanently scarred, disfigured, and many times blind.

Hematopoiesis

Stem cells differentiate into lymphoid progenitors (forming B/T cells AND NK cells) or myeloid progenitors (forming all others)

Th1

T Helper 1 cell. Important in delayed type hypersensitivity, cytotoxicity, t-cell mediated autoimmunity, and graft rejection. Specifically in cell-mediated immunity: activates macrophages, opsinization for complement, and neutrophil activation. INF-Y is an important Th1 cytokine.

Th2

T Helper 2 cell that drives the antibody response. Important in humoral immunity, allergies, autoimmune diseases, and tolerance. IL-4 is an important Th2 cytokine that activates isotype switching, macrophages, and eosinophils; produces IgE.

Structure of a TCR (toll cell receptor)

TCR is a heterodimer linked by a disulfide bond. Majority of TCRs composed of one a chain and one b chain The small subset is a g d heterodimer. CD3 and zeta chain are non-covalently associated to the TCR. Expression of the TCR, CD3 and zeta chain are required for antigen recognition and signalling TCR recognizes Ag, and then CD3 and zeta chain start the signal cascade.

T cell surface molecules

TCR recognizes antigen. CD3, CD4, CD8, and CD28 are part of signal transduction. Integrins function in adhesion.

Edward Jenner's Observation

That milkmaids did not generally get smallpox. He theorized that the pus in the blisters which milkmaids received from cowpox (a disease similar to smallpox, but much less virulent) protected the milkmaids from smallpox. It was common knowledge that survivors of smallpox became immune to the disease. As early as 430 BC, survivors of smallpox were called upon to nurse the afflicted.

Immunodominant epitope

The epitope for which most of the responding T cells in a given individual is specific. Typically correspond to the peptides proteolytically generated within APCs that bind most avidly to MHC molecules

What do monocytes, macrophages, and dendrites all have in common?

The production of cytokines and chemokines

MHC haplotype

The set of MHC alleles on an individual chromosome. It can influence susceptibility to certain diseases, transplant success, and how an individual responds to certain pathogens.

Neutrophils

These are Polymorphonuclear cells (PMNs) of the INNATE immune system, and are recruited to the site of infection where they phagocytose invading organisms and kill them intracellularly (they are professional phagocytes). Attracted to sites of infection by multiple signals including bacterial products. They can contribute to tissue damage during inflammation. Make up 95% of circulating granulocytes.

Dendritic Cells

These cells of the INNATE immune system's main function is antigen processing and presentation to T-cells (they are professional APCs). A critical cell in initiating the adaptive immune response by activating naive T cells (their extensive folds=maximum contact with T cells). They have high levels of MHC and co-stimulatory molecules.

What is the function of antibodies IgM, IgG, and IgA?

They serve to directly fight infections through the neutralization of microbes and toxins. They act indirectly by activating the complement cascade (lysis, phagocytosis--enhanced by opsinization which requires Cb3, inflammation).

TLRs

Toll-like receptors are highly conserved across species. Also known as pattern recognition receptors, they recognize molecules that are broadly shared by pathogens but distinguishable from host molecules, collectively referred to as pathogen-associated molecular patterns (PAMPs). They can recognize endogenous AND exogenous antigen. They elicit a response that eventually expresses inflammatory cytokines, chemokines, and co-stimulatory molecules. Therefore, they affect innate AND adaptive immunity.

Functions of IFN-a/B

Type I IFN inhibits viral replication and inhibits viral protein synthesis.

B cell receptor (Ig)

Unlike TCR, it does NOT require MHC. It recognizes soluble intact macromolecules (proteins, lipids, polysaccharides) and small chemicals.

Primary lymphoid organs

aka. generative. Consist of bone marrow and the thymus (where T cells mature). Bone marrow is the progenitor for both B and T cells, where B cells mature, and the site of residence for long-lived plasma cells.

HEV

high endothelial venule; an enlarged epithilial lining of a lymphatic vessel that allows naive t-cells to pass through. These are NOT present in the CNS.

Lysozyme and phospholipase in tears, saliva, and nasal secretions

A chemical barrier, part of innate immunity, that breakdown the cell wall of bacteria and destabilize bacterial membranes

Fatty acids in sweat

A chemical barrier, part of innate immunity, that inhibits the growth of bacteria.

Low pH of sweat and gastric secretions

A chemical barrier, part of innate immunity, that prevents growth of bacteria

Surfactant

A chemical component of innate immunity, these are found in the lung and enhance antigen clearance.

INF-Y

A chemokine produced during the innate immune response. It strongly activates macrophages. Cytokines (IL-1, IL-12, TNF) act on NK cells and T cells, which release INF-Y to activate macrophages.

Chemokines

A large family of structurally homologous, low molecular weight cytokines that stimulate leukocyte movement and regulate the migration of leukocytes from the blood to the tissues. They are a subclass of cytokines that cause cells to move from one point to another and to stay there.

Epitope

A peptide fragment that binds an MHC molecule for recognition by TCR

Cross-reactivity

A reaction between an antigen and an antibody that was generated against a different but similar antigen. Method used in generating the smallpox vaccine (and later paved the way for all many vaccines).

Immunological Tolerance

A state of unresponsiveness for a particular antigen. It is LEARNED, very specific and induced by prior exposure to antigen. Includes tolerance to non-self antigen. - Immunological tolerance is NOT simply a failure to recognize an antigen..It IS an active response to a particular epitope and is just as specific as an immune response. Tolerance can be natural (self tolerance, oral tolerance)...or induced (e.g.- prevent allergies, graft rejection or autoimmunity).

Consequences of co-stimulatory molecules

Absence of co-stimulatory molecules= T cell will not be activated (anergy) Absence of antigen-TCR interaction= T cell will not be stimulated. Co-reception of both signals activate T cells (antigen in the context of MHC + co-stimulatory molecule (such as B7)). At the termination of the immune response, CTLA-4 replaces CD28 and downregulates T cell function. So, CD28 doesn't bind to B7--there is no co-stimulation.

Active vs. Passive Immunity

Active immunity is conferred by a host response to a microbe or microbial antigen (vaccine or infection), whereas passive immunity is conferred by adoptive transfer of antibodies (serum) or T lymphocytes (cells) specific for the microbe. Both forms of immunity provide resistance to infection and are specific for microbial antigens, but only ACTIVE immune responses generate immunologic MEMORY!

Interleukin-2 (IL-2)

Acts on T cells to affect T cell clonal expansion/differentiation. Before T cells are activated, native cells express By IL-2. After activation, it becomes a trimer of aBy IL-2, increasing affinity 1,000 FOLD! Acts on NK cells to increase proliferation and cytotoxic activity.

Phases of adaptive immunity

Adaptive immune responses consist of distinct phases, the first three being the recognition of antigen, the activation of lymphocytes, and the elimination of antigen (the effector phase). The response contracts (declines) as antigen-stimulated lymphocytes die by apoptosis, restoring homeostasis, and the antigen-specific cells that survive are responsible for memory.