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Insight into Adaptive Immunity and Host Defense Mechanisms

Explore the body's defense system against invaders with Adaptive Immunity, including lymphocytes, antibodies, lymphatic system, and antigen recognition. Study T and B cells' roles in cell-mediated and humoral immune responses. Unveil the functions of antibodies, epitopes, and the Major Histocompatibility Complex. Understand how the immune system fights foreign antigens to protect the body against infections and diseases.

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Insight into Adaptive Immunity and Host Defense Mechanisms

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  1. Adaptive Immunity Chapter 16

  2. Overview of Adaptive Immunity • Adaptive immunity is the body’s ability to recognize and defend itself against distinct invaders and their products • Adaptive Immunity only found in vertebrate animals • 4 attributes of adaptive immunity • Specificity • Diversity • Memory • Self-nonself recognition

  3. Overview of Adaptive Immunity • Involves activity of lymphocytes • Two main types of lymphocytes • B lymphocytes (B cells) • Mature in the bone marrow • T lymphocytes (T cells) • Mature in the thymus • Two types of adaptive immune responses • Humoral immune responses • B cells - antibodies • Cell-mediated immune responses • T cells

  4. Overview of Adaptive Immunity [INSERT FIGURE 16.1]

  5. Overview of Adaptive Immunity Animation: Host Defenses: Cell-Medicated Immunity: Overview Animation: Host Defenses: Humoral Immunity: Overview

  6. Elements of Adaptive Immunity • The Tissues and Organs of the Lymphatic System • Screen the tissues of the body for foreign antigens • Composed of lymphatic vessels and lymphatic cells, tissues, and organs

  7. Elements of Adaptive Immunity • The Tissues and Organs of the Lymphatic System • Lymphatic vessels and the flow of lymph • Form a one-way system that conducts lymph from local tissues and returns it to the circulatory system • Lymph is a liquid with similar composition to blood plasma, which arises from fluid leaked from blood vessels into surrounding tissues

  8. Elements of Adaptive Immunity [INSERT FIGURE 16.2]

  9. Elements of Adaptive Immunity • The Tissues and Organs of the Lymphatic System • Lymphoid organs • Primary lymphoid organs • bone marrow • Thymus • Secondary lymphoid organs • Lymph nodes • Spleen • Tonsils • Mucosa-associated lymphatic tissue (MALT)

  10. Elements of Adaptive Immunity • Antigens • Properties of antigens • Molecules the body recognizes as foreign and worthy of attack • Not all antigens are pathogenic • But the immune system does not know that • Body recognizes antigens by three-dimensional regions called epitopes • Include components of bacterial cell walls, capsules, pili, and flagella, as well as proteins of viruses, fungi, and protozoa • Food and dust can also contain antigenic particles

  11. Epitopes are specific areas of antigen that are recognized by T cell receptors and Antibodies [INSERT FIGURE 16.4a]

  12. Elements of Adaptive Immunity • B Lymphocytes (B Cells) • Arise and mature in the bone marrow • Found primarily in the spleen, lymph nodes, and MALT • Small percentage of B cells circulate in the blood • Major function is the secretion of antibodies

  13. Elements of Adaptive Immunity • Antibodies • Can be secreted by B cells or found on the surface of the B cell • Has a variable region • This gives the antibody specificity (the variable region is specific for a specific epitope) • Has a constant region • This is what makes the antibody IgM, IgD, IgG, IgE or IgA • Due to gene rearrangement in a developing B cell, all the antibodies a given B cell will make will have the same variable region (same specificity)

  14. Elements of Adaptive Immunity [INSERT FIGURE 16.6]

  15. Elements of Adaptive Immunity • B Lymphocytes (B Cells) and Antibodies • Classes of antibodies • Threats confronting the immune system are variable • The class involved in the immune response depends on the type of foreign antigen, the portal of entry, and the antibody function needed, the stage of the infection • Five different classes of antibodies • IgM, IgD, IgG, IgE, IgA

  16. [INSERT TABLE 16.1]

  17. Elements of Adaptive Immunity • Antibody function • Plan the “kiss of death” on antigen • Antibodies function in several ways • Activation of complement and inflammation • Neutralization • Opsonization • Killing by oxidation • Agglutination • Antibody-dependent cellular cytotoxicity (ADCC) • B Lymphocytes (B Cells) and Antibodies

  18. [INSERT FIGURE 16.7]

  19. Elements of Adaptive Immunity Animation: Host Defenses: Humoral Immunity: Antibody Function

  20. Elements of Adaptive Immunity • T Lymphocytes (T Cells) • Produced in the bone marrow and mature in the thymus • Circulate in the lymph and blood and migrate to the lymph nodes, spleen, and Peyer’s patches • T cells have T cell receptors (TCRs) on their cytoplasmic membrane • Have specificity to antigen

  21. Specificity of the T cell receptor (TCR) • TCRs do not recognize epitopes directly • TCRs only bind epitopes associated with a MHC protein • MHC – Major Histocompatibility Complex • proteins found on surface of our cells – antigen presenting molecules • MHC Class I – found on all of our nucleated cells, will present antigen from a virus or other intracellular pathogen that has invaded the cell • MHC Class II – found on antigen presenting cells (B cells, macrophages, dendritic cells), will present antigen that it has phagocytized • WILL TALK MORE ABOUT THESE AGAIN IN A FEW SLIDES

  22. Elements of Adaptive Immunity [INSERT FIGURE 16.8]

  23. Elements of Adaptive Immunity • T Lymphocytes • Types of T lymphocytes • Cytotoxic T lymphocyte, Tc • Recognizes antigen in MHC Class I, Kills cells that have been infected with virus, cancer cells • Helper T lymphocyte, TH • Recognizes antigen in MHC Class II, functions to upregulate the activities of B cells and cytotoxic T cells • Regulatory T lymphocyte • represses adaptive immune responses to reduce autoimmunity

  24. Clonal Deletion • Vital that immune responses not be directed against autoantigens • Body eliminates self-reactive lymphocytes via clonal deletion • Lymphocytes that react to autoantigens undergo apoptosis

  25. Clonal Deletion • Want to first make sure TCR does recognize MHC • If it doesn’t, apoptosis • Next it is presented MHC + autoantigen • Don’t want a TCR that recognizes self antigens • If it recognizes autoantigen+MHC, apoptosis • Will end up with T cells with TCRs that recognize MHC but not autoantigen • Therefore, they will only react with MHC that is presenting foreign antigen

  26. Clonal deletion and antibodies

  27. Immune System Cytokines • Soluble regulatory proteins that act as intercellular signals when released from certain body cells • Immune system cytokines secreted by various leukocytes • The complex web of signals among all the cell types of the immune system is referred to as the cytokine network

  28. Immune System Cytokines • Interleukins (ILs) – signal among leukocytes • Interferons (IFNs) – antiviral proteins that may act as cytokines • Growth factors – proteins that stimulate stem cells to divide • Tumor necrosis factor (TNF) – Secreted by macrophages and T cells to kill tumor cells and regulate immune responses and inflammation • Chemokines – chemotactic cytokines that signal leukocytes to move

  29. Preparation for an Adaptive Immune Response • The Roles of the Major Histocompatibility Complex (MHC) • Group of antigens first identified in graft patients • Important in determining the compatibility of tissues in successful grafting since they are found on the surface of all of our cells • Major histocompatibility antigens are glycoproteins found in the membranes of most cells of vertebrate animals • Function to hold and position antigenic determinants for presentation to T cells

  30. Preparation for an Adaptive Immune Response • The Roles of the Major Histocompatibility Complex • Antigens bind in the antigen-binding groove of MHC molecules • Two classes of MHC proteins • MHC class I • Found on every cell • Will present antigen if cell has been infected (endogeneous antigens) • MHC class II • Found on antigen presenting cells (B cells, macrophages, dendritic cells) • Present antigen that they have processed after phagocytosis (exogeneous antigens)

  31. Preparation for an Adaptive Immune Response • Antigen Processing • Antigens must be processed for MHC proteins to display epitopes • Antigen processing occurs by different processes for endogenous and exogenous antigens

  32. Preparation for an Adaptive Immune Response Animation: Host Defenses: Antigen Processing and Presentation: Overview

  33. Endogeneous antigen processing • Infected cell • Presented on MHC class I

  34. Exogeneous antigen processing • Foreign entity phagocytized by antigen presenting cell • Presented on MHC Class II

  35. Let’s go over a couple of scenarios • A B cell is going along and encounters an epitope on a bacteria that its membrane-bound IgM antibody is specific for • It phagocytizes the bacteria and processes the antigen • It puts some of that antigen on its MHC Class II molecules on it’s surface • A T helper (TH) cell with a TCR that recognizes the antigen in the MHC comes by • Interaction of the TCR and MHC causes a release of cytokines by the TH cell • Those cytokines induce a signal transduction pathway in both the T and B cell specific for this bacteria • Results in mitosis of these specific B and T cells • Results in the B cell secreting more of this specific antibody (will put the variable region on an IgD, IgG, IgE, and IgA antibody) • Results in the B and T cells with specificity for this bacteria to make memory cells of themselves (will last for decades)

  36. A cell is infected by a virus • The cell is able to take some of the viral particles and put them on the MHC Class I molecules it has on its surface • A cytotoxic T (Tc) cell with specificity for that virus comes by and recognizes the antigen and MHC • Interaction of the TCR on the Tc cell and MHC molecule results in release of perforin by the T cell • Perforin causes holes in the surface of the infected cell, cell is forced to go through apoptosis • Goal is to kill the self cell before the virus is able to replicate and kill more cells

  37. Cell-Mediated Immune Responses [INSERT FIGURE 16.14]

  38. Viral infected cells

  39. Cell-Mediated Immune Responses • Memory T Cells • Some activated T cells become memory T cells • Persist for months or years in lymphoid tissues • Become functional immediately upon subsequent contacts with epitope specific to its TCR

  40. Cell-Mediated Immune Responses • T Cell Regulation • Careful regulation of cell-mediated immune response to prevent T cells from responding to autoantigens • T cells require additional signals from an antigen-presenting cell • Interaction of the T cell and antigen-presenting cell at an immunological synapse stimulates the T cell to respond to the antigen

  41. Humoral Immune Responses • Memory B Cells and the Establishment of Immunological Memory • If you have never encountered an antigen, your immune system is naive to that antigen • Primary Immune Response is the adaptive immunity’s first exposure to that antigen • It can take up to 2 weeks for B and T cells to become fully upregulated • If there is recovery, memory B and T cells will be in circulation • Secondary immune response happens when you encounter that same antigen again • Memory B and T cells will become activated, much quicker response

  42. Humoral Immune Responses

  43. Types of Acquired Immunity • Specific immunity acquired during an individuals life • Two types • Naturally acquired – immune response against antigens encountered in daily life • Artificially acquired – response to antigens introduced via a vaccine • Further distinguished as either active or passive • Active – active response to antigens via humoral or cell-mediated responses • Passive – passively receive antibodies from another individual

  44. Vaccination • Simulates primary response • Therefore, when you come into contact with pathogen, secondary response happens • Results in no sickness or slight sickness with quick recovery

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