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44 Cards in this Set
- Front
- Back
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Why are viruses inaccessible to antibodies and other soluble mediators such as complement
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Because they reside within the cytoplasm of infected cells
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What is the only way to eliminate a virus from the body
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Eliminate the infected cell
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Name some important viruses
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Hepatitis B, Influenza, Herpes simplex, Cytomegalovirus, Epstein-Barr, Human immunodeficiency
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What are the two main innate effector mechanisms that defend the body against viruses
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Type 1 interferons; NK cell-mediated killing of infected cells
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What cells produce IFN-alpha
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mononuclear phagocytes (leukocyte interferon)
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Why are viruses inaccessible to antibodies and other soluble mediators such as complement
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Because they reside within the cytoplasm of infected cells
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What cells produce Interferon-beta
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Many cells, including fibroblasts (fibroblast interferon)
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When is interferon produced
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When viral double-stranded RNA (PAMP) is recognized by a Toll-like receptor
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What is the mode of action of interferon
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Paracrine. It induces MHC class 1 expression to enhance presentation of viral antigens to CD8 cells. It also induces IL-12 receptor expression by CD4 T cells
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How do NK cells mediate killing of infected cells
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Many viruses attempt to inhibit MHC class 1 expression by the infected cells. Using inhibitory receptors that recognize MHC class 1, NK cells detect the loss of MHC class 1 expression and become activated
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Who are the two main players in adaptive immunity to viruses
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Cytotoxic T lymphocytes and Antibodies
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What is required for a robust CD8 T cell response
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CD4 T cell help
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How do cytotoxic T lymphocytes mediate killing of infected cells
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They secrete perforin and granzyme and express FasL. They can also cause pathology, as with Hepatitis B
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During what viral stage are antibodies effective
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Extracellular stages
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Which immunoglobulin plays an important role in blocking viral entry at mucosal surfaces
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Secretory IgA
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How do viruses evade the immune system
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Antigenic variation; Inhibition of antigen presentation by MHC class 1; Production of proteins which antagonize immune responses; Target immune system cells
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What are some example of intracellular bacteria
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Mycobacterium tuberculosis, Mycobacterium leprae, Leigonella pneumophila, Listeria monocytogenes
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Who are the three important players in innate immunity to intracellular bacteria
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Phagocytes (neutrophils and macrophages); NK cells (important source of IFN-gamma); Cytokines (IL-12, which stimulates production of IFN-gamma by NK cells and development of CD4 Th1)
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What role do CD4 T cells play in adaptive immunity to intracellular bacteria
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Stimulated to become Th1 by IL-12. Express CD40L and IFN-gamma.
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What type of hypersensitivity does macrophage activation by CD4 T cells cause
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Delayed type (IV) hypersensitivity
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Histologically, what is extensive macrophage activation by CD4 T cells described as
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Granulomatous inflammation
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What role do Cytotoxic T lymphocytes play in adaptive immunity to intracellular bacteria
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Crucial for controlling some intracellular bacterial infections (Listeria monocytogenes) which readily escape from the phagolysosome into the cytoplasm
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In humoral immunity to intracellular bacteria, what stimulates B cells to class switch
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IFN-gamma produced by CD4 T cells (Th1)
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What are some methods of immune evasion by intracellular bacteria
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Inhibition of phagolysosome function (M. tuberculosis, L. pneumophila)
Neutralization of ROI (M. leprae) Escape into cytoplasm (L. monocytogenes) |
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Who are the important players in adaptive immunity to intracellular bacteria
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CD4 T cells (activate macrophages)
CTL (kill the escapees from the phagolysosome) Humoral immunity (B cell class switching) |
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How do extracellular bacteria mediate pathology
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By inducing inflammation and directly producing toxins that damage host cells and tissues
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What are some examples of extracellular bacteria
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Meisseria spp.; Eschericia coli; Staphylococcus aureus; Streptococcus pyogenes
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What are some common players in innate immunity to extracellular bacteria
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Complement, phagocytes, innate response to LPS, Fever/pyrexia, Acute phase reactants
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How does complement aid in innate immunity to extracellular bacteria
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The alternative pathway of complement activation is directly activated by components of bacterial cell walls, as well as the mannose-binding lectin (MBL) pathway. Complement enhances phagocytosis of bacteria through opsonization, directly mediates bacterial cell lysis by formation of MACs, and generates inflammatory mediators that attract and activate phagocytes
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How do phagocytes aid in innate immunity to extracellular bacteria
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They express scavenger receptors, complement receptors, and Toll-like receptors that allow them to phagocytose bacteria and become activated to kill
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What are the innate responses to LPS
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LPS binds to TLR-4, and induces inflammation that both enhances bacterial killing and mediates pathology. LPS has potent effets on macrophage activation, as well as other phagocytes. It can induce cytokine production and the respiratory burst, and cause the "left shift"
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What role does fever play in innate immunity to extracellular bacteria
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Fever can be helpful in limiting bacteria replication. Pyrogens can be derived from bacteria or may be synthesized by the body
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What are acute phase reactants
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Serum plasma proteins that serve to protect the body from bacterial infection. They include C-reactive protein, fibrinogen, and serum amyloid A. They are stimulated by cytokines such as TNF, IL-1, and IL-6
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In adaptive immunity to extracellular bacteria, what role does humoral immunity play
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Antibodies produced by B cells are the primary mechanism of adaptive immunity to extracellular bacteria
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What are some complications of immune response to extracellular bacteria
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Septic Shock (respiratory distress and decreased liver function); Toxic Shock Syndrome (massive polyclonal activation of CD4 T cells); Rheumatic fever (Type II hypersensitivity); Poststreptococcal glomerulonephritis (antigen deposit in glomeruli)
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What are some tactics used by extracellular bacteria to evade the immune system
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Antigenic variation; Inhibition of complement activation; Resistance to phagocytosis; Inactivation of ROI
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What is unique about fungi
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They are opportunistic pathogens, usually causing infections in the immunocompromised
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What is the innate immune system response to fungi
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Phagocytes, such as neutrophils and macrophages
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What is the adaptive immune system response to fungi
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Cell mediated immunity, such as granulomatous inflammation
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What is the adaptive immune response to protozoa
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Cell mediated immunity (Th1 responses) and Humoral immunity (in the extracellular stages)
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What is the innate immune response to helminths
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There is none
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What is the adaptive immune response to helminths
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Th2 responses primarily. IL-4 (class switching to IgE) and Il-5 (stimulates eosinophils). Eosinophils use FceR1 to recongize IgE, and release major basic protein. Mast cells and basophils also express FceR1
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How do parasites evade the immune system
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Antigenic variation and resistant surface coats
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What are some complications of immune responses to parasites
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Delayed-type hypersensitivity and immune complex deposition
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