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The Immune System Overview

The Immune System Overview. The specific immune system is mediated by leukocytes = white blood cells ( wbcs ). P hagocytosis : wbcs engulf invading organisms and destroy them Macrophages are large, long-lived phagocytic cells c ontaining many lysosomes.

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The Immune System Overview

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  1. The Immune System Overview The specific immune system is mediated by leukocytes = white blood cells (wbcs)

  2. Phagocytosis: wbcs engulf invading organisms and destroy them Macrophages are large, long-lived phagocytic cells containing many lysosomes

  3. Macrophages are found in the lymphatic system

  4. Antimicrobial proteins attack microorganisms • Complement system—30 proteins interact in a • series of steps that results in lysis of invaders

  5. Interferons—produced by virus-infected cells to help other cells resist infection; tell other cells to make proteins that inhibit viral replication

  6. The Inflammatory Response • Blood supply increases to area of injury • Histamine made by mast cells dilates vessels • Phagocytes arrive to destroy pathogens

  7. Immune system = 3rd line of defense • Specific • Diverse • Self-nonselfrecognition • Memory Humoral response: B cells Cell-Mediated response: Cytotoxic T cells Both activated by Helper T cells

  8. B and T cells are lymphocytes (specific type of leukocyte) made in the bone marrow B cells mature in the bone marrow. T cells mature in the thymus.

  9. Antigen—a foreign substance that elicits a specific response by lymphocytes Antibody—antigen-binding immunoglobulin produced by B cells Antibodies and antigen receptors on the membranes of lymphocytes recognize and distinguish among antigens.

  10. Epitopes—small, accessible portions of an antigen to which antibodies bind

  11. Antibodies = Immunoglobulins (Igs): have 2 heavy chains and 2 light chains joined by disulfide bridges C regions = constant V regions = variable (antigens bind to V regions)

  12. Each lymphocyte will recognize and respond to ONE and ONLY ONE antigen. Specificity is determined during development before any antigens are encountered.

  13. When an antigen binds to the receptors, those specific lymphocytes are activated and begin to divide. Plasma cells secrete antibodies. They are also called effectorcells. Clonal selection: producing clones of cells that will destroy a particular antigen Memory cells: stick around until the next time the antigen appears

  14. Primary vs. Secondary Immune Response

  15. The immune system distinguishes self from nonself —> no lymphocytes are reactive against the body’s own molecules. An autoimmune disorder is when this system fails and the immune system destroys the body’s own tissues.

  16. MHC = major histocompatibilitycomplex • group of glycoproteins embedded in the cell membrane • “self-markers” • Class I MHCs on ALL nucleated cells • Class II MHCs only on macrophages, • B cells, and activated T cells • MHC = “Self” • Antigen = “Nonself”

  17. Class I MHC molecules present antigens to cytotoxicT cells. Class II MHC molecules present antigens to helper T cells.

  18. Humoralresponse— ANTIBODIES fight against pathogens outside of cells Cell-mediated response— T cells fight against pathogens that have already infected cells

  19. B cells and macrophages are antigen-presenting cells (APCs). Class II MHC molecules present the antigens to helper T cells and bind to CD4on the helper T cell membrane. When bound to MHC II, the helper T cells proliferate. Helper T cells activate both the humor and the cell-mediated responses. Cytokines (interleukins) signal other lymphocytes (B or T cells) to proliferate as well.

  20. When cytotoxic T cells are activated, they kill infected cells. CD8 (on the membrane of cytotoxic T cells) binds to class I MHCs. When it recognizes a foreign antigen, it kills the cell by releasing perforin. Cell-Mediated Response

  21. Humoral Response Helper T cells and free floating antigens stimulate B cells to proliferate to make Ab-secreting plasma cells & memory cells. B cells present antigens on class II MHCs to make even more B cells!

  22. Disposal of antigens by antibodies

  23. Active immunity can be acquired naturally (after exposure to an antigen) or artificially (by a vaccine). Vaccines are inactivated toxins that still have the epitopes available to trigger an immune response. Then if the antigen is actually encountered, the immune response will be quicker (secondary response) Passive immunity— mom to baby

  24. Achoo! Allergies! IgEsfor pollen bind to mast cell. When pollen binds, mast cell releases histamine triggers vessel dilation, increased permeability sneezing, etc. Anaphylactic shock—acute allergic response when so many mast cells release histamine that there’s a dramatic drop in blood pressure. Epinephrine counteracts this response.

  25. Immunodeficiency diseases—parts of the immune system fail to function properly. AIDS is an immunodeficiency disease caused by the HIV virus. HIV infects cells that have surface CD4 receptors (helper T cells). Fusin (CXCR-4)and CCR5 are coreceptors that help the virus to enter cells.

  26. Antibodies to the virus increase, and the virus levels drop initially. But its DNA is still present and replicating. And cells continue to be damaged.

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