PSL301H Blood and Immune System Adaptive Immunity PDF

PSL301H—Blood and Immune System Adaptive Immunity and B cells Learning objectives List the four features of adaptive immunity Describe how these features are achieved Describe how B cells are activated Describe how antibodies protect us  Defence against pathogens Innate Immunity...

PSL301H—Blood and Immune System Adaptive Immunity and B cells Learning objectives List the four features of adaptive immunity Describe how these features are achieved Describe how B cells are activated Describe how antibodies protect us  Defence against pathogens Innate Immunity rapid, non-specific Adaptive Immunity slower, antigen- specific Figure from Interactive Physiology  What are the features of adaptive immunity? Specificity – activated by and responds to a specific antigen Versatility – ready to confront any antigen at anytime Memory – “remembers” any antigen it has encountered Tolerance – responds to foreign substances but ignores normal tissues Figure from Interactive Physiology Antigens Antibody  How are these features achieved? 1. Specificity –responds to a specific antigen Both B and T cells have receptors that recognize specific shapes 2. Versatility – ready to confront any antigen at anytime Different B and T cells have different receptors 3. Memory – “remembers” any antigen it has encountered Some activated B and T cells are long lasting 4. Tolerance – responds to foreign substances but ignores normal tissues B and T cells with receptors that recognize self are deleted or not activated (1) Specificity & (2) versatility of B and T cell receptors B cells T cells Figure from Interactive Physiology B cell receptors bind to extracellular antigens Figure from Interactive Physiology Antibody (immunoglobulin)-like molecule T cell receptors bind to antigens displayed on the surface of cells (macrophages, tissue cells, etc) T cell receptor Viral antigen Major histocompatability complex Figure from Interactive Physiology T and B cells circulate throughout the body searching for antigen Encounter antigen in secondary lymphoid tissues Figure from Interactive Physiology  Clonal selection, expansion and memory Primary and Secondary Immune Responses i.e. (3) Memory B and T lymphocytes originate in the bone marrow Need to be educated i.e. (4) Tolerance T cells undergo positive and negative selection in the thymus B cells undergo positive and negative selection in the bone marrow Figure from Interactive Physiology  Focus: B cells and Humoral Immunity B cells make antibodies Every human has between 107 and 109 different shaped Fabs  How are B cells activated? 1. Antigen binds to specific B cell via B cell receptors 2. Antigen is internalized, digested and combined with MHC and then transported to cell surface B cell MHC receptor B cell Antigen Modified figure from Interactive Physiology 2. Specific helper T cell recognizes antigen and MHC becomes activated and secretes cytokines T cell receptor MHC B cell receptor B cell Helper T cell Antigen + cytokines (IL-4, IL-5, IL-6) Modified figure from Interactive Physiology 3. Activated B cytokines cell divides. Some daughter cells become plasma cells and secrete antibodies, others become memory B cells Figure from Martini (2006) Fundamentals of Anatomy and Physiology Summary B cell receptor Figure from Martini (2006) Fundamentals of Anatomy and Physiology  How do antibodies protect us? Copyright © 2010 Pearson Education, Inc.  Classes of antibodies Most common type of circulating antibody Transferred across the placenta from mother to baby First type of antibody to be secreted in response to a new antigen Good at causing antigen clumping and activating complement IgA Crosses epithelial cells. Protects epithelial surfaces and present in breast milk IgE Fights parasites. Eosinophils have receptors for the IgE. Release histamine. Associated with allergic reactions IgD Are the B cell receptors on the surface of B cells Figure from Interactive Physiology  Figure from Interactive Physiology Types of adaptive immunity Exposure to a Transfer of Ab pathogen. Long- from another lasting generates organism. Lasts memory B and T about 3 months cells because Ab degraded Vaccination Vaccination with with antigen antibodies Coordination of innate and specific immune system: response to extracellular bacteria External environment Skin or mucous membrane ECF lyses coat Bacteria Membrane attack complex Opsonins activate present make ingest and act as disable antigens to Complement activate proteins Mast cells are secrete Acute phase Phagocytes TH cells proteins Chemotaxins Histamine activate increases B lymphocytes permeability become secrete Antibodies Plasma cells act as Plasma proteins Capillary Circulating leukocytes attract  Summary Features of adaptive immunity: Specific, versatile, has memory, tolerant to self Features achieved by T and B cells having different receptors with different specificities, the generation of memory cells and deletion or inactivation of T and B cells that react to self B cells are activated through binding to antigen to B cell receptors, presentation on MHC class II, activation of specific helper T cells, generation of plasma cells that secrete Ab Antibodies protect us by binding to antigen blocking the action of the antigen and further activating the immune system