# Test 2, Lecture 12 Two fundamental types of immune response Product of humoral immunity; product of cellular immunity product of humoral immunity soluble circulating immunity; immune molecules are antibodies; manufactured by B-cells; antibodies bind and immobilize antigens product of cellular immunity killer T lymphocytes (cytotoxic T cells); CTL recognize viral Ag on surface of infected cells then kill the cells B cells mature into plasma cells, which secrete antibodies T cells mature into cytotoxic T cells (CTLs) or helper T cells B cells are recognized by... a surface IgM antibody Antibody molecules are composed of these types of polypeptides heavy chain (long polypeptide) and light chain (short) Variable region of antibody amino terminal portion of both chains; varies between Ab; determines Ag-Ab specificity Constant region of antibody identical among Ab of same class; determines class Ig classes differ in... constant region Structural feature of IgM pentamer IgM is displayed... as a monomer on the surface of B cells Earliest responding Ig class IgM IgM-Ag complex... activates complement and macrophage IgD is found... on the surface of many B cells IgD stimulates... differentiation to other classes, such as IgM --> IgG The primary circulating Ab class IgG IgG is important for... immunity (2nd invasion) IgG stimulates... complement and macrophage IgA is secreted... into lumen of many organs (respiratory tract, intestinal tract) The Ab at port of entry IgA B cells are made here bone marrow If Ag binds to IgM on B cell surface, these events occur proliferation (cell division), Ab secretion (differentiation) Memory cells B cells which provide rapid secondary response T cells are made here Thymus CTLs are recognized by... CD8 Helper T cells are recognized by... CD4 Basic function of Helper T cells Coordinate immune response CTLs function by... binding to surface Ag and then destroying the cell. They proliferate when stimulated by Ag, and produce memory cells. Helper T cells function by... Binding Ag on surface of macrophage; coordinate all parts of immune response; secrete factors that influence themselves and other cells. The factors secreted by T_H cells are called lymphokines, most of which are interleukins IL-2 Lymphokine for T cell growth stimulation; stimulation of Ab secretion by B cells IFN-gamma Lymphokine for macrophage activation; Ig class switching by B cells IL-4 Lymphokine for B-cell activation; Ig class switching by B cells; T cell growth stimulation; Macrophage activation Macrophage Phagocytic cell, digests and displays Ag to activate immune response Complement Family of proteins that coat and destroy Ag MHC Major histocompatibility complex; cell surface proteins on immune cells that help display antigen; signals self (that a cell is part of the organism and should not be targeted); CTL requires MHC I and Ag to bind; T_H requires MHC II and Ag to bind Immune response to virus Viral infection elicits most vigorous immune response; virions stimulate B cells; infected cells stimulate T cells Humoral response to virus IgM and IgG handle disseminated infections; IgA handles localized infections; neutralization Neutralization of virus Decrease in infectivity due to attachment of Ab; Binding to protein responsible for uncoating is most effective; One neutralizing Ab in right place is sufficient Why Ab targeting of uncoating protein is most effective There is just one target. Receptor epitopes are numerous, and would require many antibodies neutralize them all. Why viral cellular response is better than neutralizing Ab Infected cells are removed; More Ag available for attack, since all viral components are displayed and not just surface Ag; Able to remove multi-nucleated syncytia (cells fused with each other to form giant cells with multiple nuclei) Levels of immunity Extent and severity of primary infection influences quality of immunity; disseminated infection with viremia (life-long immunity, all systems involved, lots of memory cells); localized infection (short and weak immunity, mainly IgA, few memory cells) Vaccines work by... using a non-pathogenic form of pathogenic virus to mimic primary infection; subsequent encounter with pathogenic virus is blocked by immunity Attenuated virus vaccine Live virus, non-pathogenic form Inactivated virus Killed virus, chemically treated Component vaccine Molecular component of virus (subunit; peptide; anti-idiotype; recombinant viral vector) Anti-idiotype vaccine Generate Ab to another Ab. Inject the virus into an organism, let it develop antibodies. Take the antibodies and inject them into a different organism, let it develop antibodies to the antibodies. Take the new antibodies and inject them into a human, which will now develop antibodies that work against the original virus with the same shape.