Antigen-antibody Binding

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 Antigen-antibody binding  An antigenic determinant or epitope is the precise area of an antigen recognized by a specific antibody  The Fab portion of the antibody, called the antigen-binding site, matches with the epitope  The antigen fits into the antigen-binding site and is held there by noncovalent chemical interactions Function of antibodies  The chief function of antibodies is to protect against infection  They can directly neutralize infectious agents or their toxic products  Antibodies can also indirectly protect the host by covering sites on microorganisms needed for attachment, preventing infection Antibody Functions  Antibodies can induce neutralizing antibody production  Antibodies can protect against infection through agglutination or precipitation  Antibodies can neutralize viruses or bacterial toxins  Antibodies can activate components of innate immunity, including complement and phagocytes Monoclonal Antibodies  Monoclonal antibodies are produced in the laboratory from one cloned B cell  They have a single class, specificity, and function  Advantages of monoclonal antibodies include known antigenic specificity, constant binding affinity, and ability to be diluted to a constant titer IgE Function  Soluble antigens from a parasitic infection cause production of IgE antibodies by B cells  IgE binds to specific receptors on mast cells  Cross-linking of IgE on mast cells leads to mast cell degranulation and release of proinflammatory products  Eosinophil chemotactic factor of anaphylaxis (ECF-A) attracts eosinophils, which attach to parasites and release lysosomal enzymes to damage microorganisms Importance of Antibodies  Antibodies are highly purified and used to develop specific and sensitive laboratory tests and therapies  Monoclonal antibodies are used as immunotherapies for certain cancers Role of IgE  IgE protects against infection by large parasitic worms  When produced against harmless environmental antigens, IgE is the primary cause of common allergies Response to Large Multicellular Parasites  IgG, IgM, and IgA bind to parasite surfaces, activate complement, and attract phagocytic cells  Eosinophils, with their special granules, can adequately damage parasites Role of IgE in Parasitic Infection  IgE initiates an inflammatory reaction that attracts eosinophils to the site of infection  Elevated levels of IgE are commonly found in parasitic infections Secretory Immune System  This immune system protects external surfaces through lymphoid tissues and secreted antibodies  Plasma cells in various sites secrete antibodies in bodily secretions to prevent infection Role of IgA  IgA is the dominant secretory immunoglobulin  It prevents the attachment and invasion of pathogens through mucosal membranes Internalization of IgA  IgA is internalized along with the epithelial receptor, resulting in the secretion of secretory IgA (sIgA)  Lymphoid tissues of the secretory immune system are connected, allowing for the secretion of specific antibodies into breast milk when foreign antigens are present in a mother's gastrointestinal tract  Colostral antibodies found in breast milk's colostrum can protect newborns against infectious agents that enter through the gastrointestinal tract Primary and Secondary Immune Responses  The immune response to an antigen is divided into two phases: primary and secondary responses  During the primary response, there is a lag phase followed by the production of IgM antibodies and later IgG antibodies  If no further exposure to the antigen occurs, the circulating antibody is catabolized, but the immune system remains primed  In a secondary response, a subsequent exposure to the antigen results in a more rapid and larger production of antibodies, primarily IgG  Natural infection or some vaccines can result in long-lasting protective antibodies Cell-Mediated Immunity and T-Lymphocyte Function  Effector T cells play a complex role in cell-mediated immunity  T cell subsets include Th cells, T memory cells, Tc cells, Treg cells, and T lymphokine-producing cells  Tc cells attack and destroy cells with intracellular antigens  Treg cells suppress the immune response  T lymphokine-producing cells secrete cytokines that activate other cells Quick Check  The major classes of antibodies are...  The major functions of antibodies are...  The difference between the secretory and systemic immune systems is...  The terms primary and secondary immune response refer to... Role of T-Cytotoxic Lymphocytes (Tc cells)  Tc cells are responsible for the cell-mediated destruction of abnormal cells, such as tumor cells or cells infected with viruses  To destroy abnormal cells, Tc cells directly adhere to the target cell through antigen presented by MHC class I molecules and CD8  By attaching to the target cell, Tc cells activate multiple killing mechanisms, leading to apoptosis of the target cell Killing Mechanisms of Tc cells  Tc cells recognize endogenous antigens presented by MHC class I molecules  Tc cells induce apoptosis of the target cell through various killing mechanisms  Tc cells can recognize antigens on the surface of almost any type of abnormal cell Other cells involved in killing abnormal cells  Natural Killer (NK) cells are a special group of lymphoid cells that can kill target cells through receptors that recognize abnormal surface changes  NK cells lack antigen-specific receptors, instead, they express a variety of cell surface activation receptors  If MHC class I antigen presentation has occurred, Tc cells provide the target cell killing