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Internal Defense: Understanding the Immune Response

This chapter explores the internal defense mechanisms of the immune system, including nonspecific and specific immune responses. Topics covered include antigens, antibodies, invertebrate immune responses, soluble molecules, cytokines, complement proteins, phagocytes, inflammatory response, cell-mediated immunity, antibody-mediated immunity, and immune system cells.

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Internal Defense: Understanding the Immune Response

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  1. Chapter 43 Internal Defense

  2. Immunology • Study of internal defensive responses • Immune response • Recognizing foreign or dangerous macromolecules • Responding to eliminate them

  3. Human immune response

  4. Nonspecific immune responses • Provide general and immediate protection • Pathogens • Some toxins and drugs • Cancer cells

  5. Specific immune responses • Highly specific • Include immunological memory

  6. Antigen • Molecule specifically recognized as foreign or dangerous by cells of the immune system • Antibodies • Highly specific proteins that recognize and bind to specific antigens

  7. Invertebrate immune responses • Always nonspecific • Physical barriers • Cuticle • Skin • Mucous membranes

  8. Phagocytosis • Antimicrobial peptides • Soluble molecules that destroy pathogens

  9. Phagocytosis

  10. Vertebrate nonspecific immune responses • First-line defenses • Physical barriers • Skin • Mucous linings of the respiratory and digestive tracts • Other nonspecific defenses

  11. Soluble molecules important in immune responses • Antimicrobial peptides • Regulatory peptides • Proteins that destroy pathogens

  12. Cytokines • Signaling proteins that regulate interactions between cells • Interferons • Inhibit viral replication and activate natural killer cells

  13. Interleukins • Help regulate interactions between lymphocytes and other cells of the body • Some have widespread effects

  14. Chemokines • Attract, activate, and direct the movement of certain cells of the immune system • Tumor necrosis factors (TNFs) • Kill tumor cells and stimulate immune cells to initiate an inflammatory response

  15. Complement proteins • Enhance the inflammatory response • Lyse the cell wall of pathogens • Coat pathogens, enhancing phagocytosis • Attract white blood cells to the site of infection

  16. Phagocytes destroy bacteria • Neutrophils • Macrophages • Natural killer cells (NK cells) • Destroy cells infected with viruses • Destroy foreign or altered cells such as tumor cells

  17. Inflammatory response • Triggered when pathogens invade tissues • Vasodilation • Increased blood vessel diameter

  18. Increased capillary permeability • Allows fluid and antibodies to leave the circulation and enter the tissues • Increased phagocytosis

  19. In response to tissue injury, several types of molecules in the plasma that mediate inflammation are activated • Mast cells release histamine and other compounds that cause vasodilation and increased capillary permeability

  20. Cell-mediated immunity • Specific T cells are activated • Proteins released that destroy cells infected with viruses or other intracellular pathogens

  21. Antibody-mediated immunity • Specific B cells are activated • Multiply and differentiate into plasma cells, which produce antibodies

  22. Immune system cells • Lymphocytes • Develop from stem cells in the bone marrow • T cells • B cells • Antigen-presenting cells (APCs)

  23. Lymphocytes and antigen-presenting cells

  24. T cells • Responsible for cell-mediated immunity • T cytotoxic cells (TC cells) • T helper cells (TH) • Memory T cells

  25. Distinguished by T-cell receptors (TCRs) • Thymus gland confers immunocompetence on T cells by making them capable of distinguishing between self and non-self

  26. B cells • Responsible for antibody-mediated immunity • Differentiate into plasma cells • Produce antibodies

  27. Some activated B cells become memory B cells • Continue to produce antibodies after an infection has been overcome

  28. Antigen-presenting cells (APCs) • Display foreign antigens as well as their own surface proteins • Macrophages • B cells

  29. Dendritic cells • Located in tissues that interact with the environment • Specialized to process, transport, and present antigens

  30. Major histocompatibility complex (MHC) • Immune responses depend on a group of genes that encode MHC proteins • Class I MHC genes • Encode self antigens, glycoproteins expressed on the surface of most nucleated cells

  31. Class II MHC genes • Encode glycoproteins expressed on APCs of the immune system • Class III MHC genes • Encode components of the complement system and TNFs

  32. Cell-mediated immunity process • Specific T cells are activated by a foreign antigen–MHC complex on the surface of an infected cell • A co-stimulatory signal and interleukins are also required • Activated TC cells multiply, giving rise to a clone

  33. Clone cells migrate to the site of infection • Pathogen-infected cells destroyed • Activated TH cells give rise to a clone of TH cells • Clone cells secrete cytokines • B cells and macrophages activated

  34. Antibody-mediated immunity process • B cells are activated when they combine with antigen • Activation requirements • APC (dendritic cell or macrophage) with a foreign antigen–MHC complex displayed on its surface • TH cell that secretes interleukins

  35. Activated B cells multiply, giving rise to clones of cells • Cloned cells differentiate, forming plasma cells • Plasma cells produce specific antibodies, immunoglobulins (Ig), in response to the specific antigens that activated them

  36. An antibody combines with a specific antigen to form an antigenantibody complex • May inactivate the pathogen • Stimulate phagocytosis • Activate the complement system

  37. Antibody structure • Y-shaped • Two arms combine with antigen

  38. Antigen- antibody complex

  39. Antibody molecule • Four polypeptide chains • Two identical heavy chains • Two shorter light chains • Chain regions • Constant (C) region and • Variable (V) region

  40. Recombination of DNA segments • Main factor responsible for antibody diversity • Occurs during the differentiation of B cells • Millions of different types of B (and T) cells are produced

  41. Immunological memory • Memory B and memory T cells remain in the body after an infection • Responsible for long-term immunity

  42. Immunological memory

  43. Primary immune response • Stimulated by the first exposure to an antigen • Secondary immune response • Stimulated by a second exposure to the same antigen • More rapid and more intense than the primary response

  44. Active immunity • Develops as a result of exposure to antigens • May occur naturally after recovery from a disease • May be artificially induced by immunization with a vaccine

  45. Passive immunity • Temporary condition • Develops when an individual receives antibodies produced by another person or animal

  46. Response to cancer cells • NK cells, macrophages, and T cells recognize antigens on cancer cells and launch an immune response against them • Cancer cells evade the immune system by blocking TC directly or by decreasing their class I MHC molecules

  47. Cancer cell destruction

  48. Human immunodeficiency virus (HIV) • Retrovirus • Causes acquired immunodeficiency syndrome (AIDS) • Destroys T helper cells • Severely impairs immunity

  49. HIV-infected T cell

  50. Graft rejection • Transplanted tissues have MHC antigens • Immune response stimulated • T cells destroy the transplant

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