Overview of Adaptive Immunity

Chapter 7 The third line of defense in the human body is adaptive immunity, which consists of lymphocytes and antibodies. Unlike innate immunity and inflammation, adaptive immunity is inducible and develops more slowly. It is highly specific to the infecting microbe and provides long-term protection through memory. The innate and adaptive immune systems are interactive and complementary, working together for complete protection against infectious disease. Bullet points Overview of Adaptive Immunity (Chapter Outline)   Adaptive immunity is the third line of defense in the human body It consists of lymphocytes and antibodies Inflammation and Adaptive Immunity    Inflammation is the "first responder" that contains the initial injury and slows the spread of infection Adaptive immunity augments the initial defenses against infection and promotes processes against reinfection Adaptive immunity develops more slowly than inflammation Differences between Inflammation and Adaptive Immunity     Inflammation is immediate, while adaptive immunity is inducible Inflammation is non-specific, while adaptive immunity is specific to the infecting microbe Inflammatory responses must be quickly removed, while adaptive immune responses are long-lived and systemic Inflammatory responses to recurrent tissue damage and infection are identical, while adaptive immune responses have memory Interaction between Innate and Adaptive Immune Systems    Components of innate resistance are necessary for the development of the adaptive immune response The adaptive immune response activates components of innate resistance Both systems are essential for complete protection against infectious disease Components of Adaptive Immune Response   Antigens are the molecular targets of antibodies and lymphocytes Antigens are generally small molecules found on the surface of microbes, infected cells, or abnormal tissues Development of lymphocytes     In the fetus, lymphocytes undergo extensive differentiation before exposure to foreign antigens Lymphoid stem cells enter the thymus and differentiate into T lymphocytes (T cells) Other stem cells enter specific regions of the bone marrow and differentiate into B lymphocytes (B cells) Each type of cell develops cell surface proteins that identify them as T or B cells   Both B and T cells develop cell surface antigen receptors, which are programmed to recognize specific antigens Before birth, each individual has produced a population of B and T lymphocytes capable of recognizing at least 108 different antigens Immune response overview        Generation of clonal diversity: lymphoid stem cells from the bone marrow migrate to either the thymus or regions of bone marrow Series of cellular division and differentiation stages result in immunocompetent T cells (from the thymus) or immunocompetent B cells (from the bone marrow) Immunocompetent cells enter circulation and migrate to secondary lymphoid organs (e.g., spleen, lymph nodes) Clonal selection: initiated by exposure to foreign antigen Antigen-presenting cells process the antigen and present it to T-helper cells (Th cells) Cooperation among APCs, Th cells, and immunocompetent T and B cells leads to cellular proliferation and differentiation Only a small population of T and B cells undergo this process at one time Cellular immunity and humoral immunity    Cellular immunity: mediated by effector T cells (T-cytotoxic cells that kill targets and T-regulatory cells that regulate the immune response) and memory T cells Humoral immunity: mediated by antibodies produced by plasma cells and memory B cells B and T lymphocytes leaving the primary lymphoid organs are immunocompetent but naive (not exposed to antigen) Distribution of lymphocytes   Immunocompetent T cells account for 60-70% of circulating lymphocytes Immunocompetent B cells account for 10-20% of circulating lymphocytes Lymphoid tissues: Sites of B-Cell and T-Cell Differentiation   Central (primary) lymphoid tissues: bone marrow (for B lymphocytes) and thymus (for T lymphocytes) Peripheral (secondary) lymphoid tissues: lymphatic vessels, lymph nodes, spleen, peripheral Peyer patches in jejunum (ileum only), bone marrow Clonal selection process in secondary lymphoid organs   Initiated when exposure to an antigen occurs Involves cooperation among various cells in the secondary lymphoid organs Key cellular interactions in clonal selection      Several subsets of B and T cells Intercellular adhesion through specific antigen receptors and intercellular adhesion molecules Production and response to multiple cytokines Activation and regulation of the immune response by T-helper cells (Th cells) Differentiation of B and T cells into effector cells (plasma cells for B cells and T-cytotoxic cells for T cells)    Suppression of inappropriate immune responses by T-regulatory cells (Treg cells) Differentiation of B and T cells into long-lived memory cells Activation of memory cells upon re-exposure to the same antigen Antibodies and effector T cells in the immune response    Antibodies defend against extracellular antigens in the blood Effector T cells defend against intracellular pathogens and abnormal cells in the blood and tissues Humoral immune response (antibodies) and cellular immune response (effector T cells) Active and passive immunity   Active immunity: develops in response to antigen, long-lived Passive immunity: temporary, preformed antibody or lymphocytes administered to an individual Clinical use of antigen or antibody   Antigen: vaccination for infectious disease protection and diagnosis Antibody: passive treatment with specific T cells for cancer, administration for early diagnosis or prevention of infection, immunotherapy for cancer treatment and prevention of entrance of environmental substances into the body Antigen and Immunogen      Antigen: molecule that can bind with antibodies or antigen receptors on B and T cells Immunogen: molecule that binds to receptors and induces an immune response All immunogens are antigens, but not all antigens are immunogens Antigens can be foreign molecules, such as infectious agents, allergens, chemical agents, and abnormal molecules on the surface of cells Size of antigen can influence its ability to induce an immune response