The complement is fixed best by which of the following immunoglobulin
Ref Harrison 17/e p2036 Upon activation, B lymphocytes proliferate and then dif- ferentiate into plasma cells that secrete different classes of antibodies with distinct functions (Fig. 4-6). There are two major mechanisms of B cell activation. * T cell-independent. Many polysaccharide and lipid anti- gens have multiple identical antigenic determinants (epitopes) that are able to engage several antigen recep- tor molecules on each B cell and initiate the process of B cell activation. * T cell-dependent. Typical globular protein antigens are not able to bind to many antigen receptors, and the full response of B cells to protein antigens requires help from CD4+ T cells. B cells also can act as APCs--they ingest protein antigens, degrade them, and display peptides bound to class II MHC molecules for recognition by helper T cells. The helper T cells express CD40L and secrete cytokines, which work together to activate the B cells. Some of the progeny of the expanded B cell clones differ- entiate into antibody-secreting plasma cells. Each plasma cell secretes antibodies that have the same specificity as the cell surface antibodies (B cell receptors) that first recog- nized the antigen. Polysaccharides and lipids stimulate secretion mainly of IgM antibody. Protein antigens, by viue of CD40L- and cytokine-mediated helper T cell actions, induce the production of antibodies of different classes (IgG, IgA, IgE). This production of functionally dif- ferent antibodies, all with the same specificity, is called heavy-chain class (isotype) switching; it provides plasticity in the antibody response, allowing antibodies to serve many functions. Helper T cells also stimulate the produc- tion of antibodies with higher and higher affinity for the antigen. This process, called affinity maturation, improves the quality of the humoral immune response. The humoral immune response combats microbes in numerous ways (Fig. 4-6). * Antibodies bind to microbes and prevent them from infecting cells, thereby "neutralizing" the microbes.
IgG
IgM
IgA
IgD
General anatomy