2. 3. • ANTIBODY FUNCTION IN HUMORAL IMMUNITY o Five Major Classes of Antibody (Know Table 23.1) (not responsible for IgDs) All classes: neutralization and agglutination 1. IgM, IgG: activates complement 2. IgG: NK cells 3. IgA: opsonization 4. IgE: histamine release from mast cells and basophils o Antibody Functions (figure 23.9) *****know for exam!! 1. Neutralization • Antibody blocks reactive groups on antigen just by binding to it 2. Agglutination • prevents colonization by clumping antigens 3. Opsonization • coats invader to attract macrophages • pathogens bound by antibodies are more efficiently engulfed by phagocytes 4. Activates complement • series of 20-30 proteins in a cascade reaction that promotes phagocytosis
• IgM, IgG 5. Enhanced Natural Killer Cell Activity • NK cells have receptors for antibody tail • Antibodies mark cells for destruction • NK cells produce pore in membrane of cells causing lysis • IgG 23.4 – CELL-MEDIATED IMMUNITY o Roles of T Lymphocytes in Cell-Mediated Immunity o Helper T Cell Activation o Cytotoxic T Cell Activation • ROLES OF T LYMPHOCYTES IN CELL-MEDIATED IMMUNITY o T Lymphocytes T cells defend against foreign or abnormal matter through direct contact 3 types: 1. Helper T Cells CD4 (T H ) o Secrete cytokines that enhance activity of B cells and other T cells o Enhance activity of macrophages and NK cells (essential to nonspecific defenses) 2. Cytotoxic T Cells CD8 (T C ) o Kill virus-infected cells, abnormal cells, and bacteria within cells 3. Suppressor T Cells o Secrete cytokines that suppress activity of B cells and other T cells o Major Histocompatibility Complex (MHC) Molecules T cells have antigen receptors • Only recognize antigen when associated with MHC molecules Antigen presentation – MHC molecules bind antigen within cell and transport antigen to surface where it can be recognized by T cells o MHC Marks Body Cells as Self 2 classes of MHC Molecules • Class I MHC – surface of all nucleated cells o Cytotoxic T cells respond • Class II MHC – surface of macrophages, activated B cells, activated T cells, and thymus cells o Helper T cells respond
MHC molecules unique to individual person = HLA (human leukocyte antigen) • Tissue Type • Marks person as “self” • Responsible for tissue/organ rejection – stimulates immune response to foreign tissue o The role of MHC molecules in antigen presentation and T cell Activation Recognition by T Cells • Helper T cells: o CD4 - binds class II MHC; enhances macrophage – T cell interaction • Cytotoxic T cells: o CD8 – binds class I MHC; enhances abnormal cell – T cell interaction Presentation of Antigens to T cells (figure 23.10) • Class I MHC molecules, which are made by all nucleated cells of the body, capture fragments of viral (or bacterial) antigens synthesized within an infected cell and transport them to the cell surface.
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- Spring '07
- cells, T Cells, Cytotoxic T cells