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Medical Microbiology Chapter 14 – Immune Responses to Infectious Agents
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Our Defense Systems Our body has 3 layers/walls of defense against pathogens and toxins 1 st = barriers 2 nd = innate responses 3 rd = antigen-specific immune responses
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Barriers Barriers – Figure 14-1
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Innate Responses Innate Responses Acute inflammation Capillary dilation Increased capillary permeability Effects? Exit of WBC to site of infection Chemokines and chemotactic factors give a chemical trail to the infection They lead to diapedesis Figure 14-3
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Innate Responses Once at the site of infection, neutrophils and macrophages carry out phagocytosis Figure 14-4 Complement Chemotactic factors Inflammation Opsonins Membrane attack complex Interferon – “interferes” with viral infections (demo on board)
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Innate Responses Fever – can be stimulated by exogenous pyrogens (LPS) or endogenous pyrogens (cytokines) Effect? Assignment Assignment
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Ag-specific Responses Key features: Must be produced after infection (usually takes 5-7 days) Specificity - B-cells and T-cells are activated by antigens (Ag) Memory – activated cells “remember” which Ag have entered the body
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Ag-specific Responses Activated B-cells produce Antibodies (Ab) These are only effective against extracellular antigens Activated cytotoxic (CD8) T-cells attack and destroy infected cells and cancer cells These are only effective against intracellular antigens
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Specific Immunity (cont.) Activation of B-cells and T-cells: Macrophages, dendritic cells, and other APCs carry out phagocytosis They then process and present the Ag on MHC II Helper (CD4) T-cells then come in contact with the APCs and become activated Helper T-cells can then “help” B-cells and cytotoxic T-cells become activated Demo on board
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Specific Immunity (cont.) B-cells come in contact with extracellular antigens (via membrane- bound Ab) Protein Ag vs. Carbohydrate Ag (for protein Ag) the Ag-Ab binding stimulates phagocytosis and Ag presentation A helper T-cell then comes and gives the “2 nd signal” for activation Once the cell is activated it proliferates and produces large amounts of Ab
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B-cell Activation Antigen B-cell
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B-cell Activation
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Helper T-cell
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B-cell Activation
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Memory Cell
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Antibody Mediated Immunity Ab Functions – Figure from other text and hand-out
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Antibody Mediated Immunity Primary and secondary responses Figure from other text
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Cytotoxic T-cell Activation Cytotoxic T-cell activation also requires helper T-cells APCs present Ag on MHC II for helper T-cells and MHC I for cytotoxic T-cells Once both cells recognize the Ag, the helper T- cells release cytokines These allow the cytotoxic T-cells to become activated Once the cell is activated it proliferates and “goes on patrol” Demo on board
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Immunizations What does an immunization do? A vaccine is made from antigens that are not harmful Leads to memory and an secondary response to the real Ag Figure from other text
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Hypersensitivity Hypersensitivity - immune reactions that occur in an exaggerated or inappropriate fashion these immune responses cause damage to host tissues
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Allergies Allergies are basically an exaggerated immune response to a harmless substance Hay fever is an allergy to plant pollen the initial exposure to the Ag generates an immune response with large amounts of IgE produced IgE can bind to mast cells and basophils and act as an Ag-receptor during the next exposure to the Ag, the Ag will bind to the IgE on a mast cell or basophil
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Allergies (cont.) this results in the release of histamine and other chemicals histamine triggers inflammation as well as runny nose, sneezing, etc. How is hay fever usually treated? Asthma is another form of allergy: the same basic process applies, but the histamine released in the lungs causes the smooth muscles to contract this closes off the air passages
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Allergies (cont.) Desensitization is a method to cure allergies the person is given repeated doses of the Ag How could this cure an allergy? this stimulates the production of IgG and IgA Neutralization of the Ag
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Transplants & Autoimmunity Transplant Rejection Why would transplanted tissues be rejected? Cytotoxic T-cells attack these cells just like they would a tumor cell or a virus-infected cell Autoimmunity - the immune system reacting against normal body proteins rheumatoid arthritis, others
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