Synthesis of an immunoglobulin in membrane bound or secretory form is determined by

Ans. c. Differential RNA processing Synthesis of an immunoglobulin in membrane bound or secretory form is determined by differential RNA processing. "B cells express a form of IgM, which is located on the cell surface. Cell surface IgM has the same specificity as the secreted IgM antibody molecule. This is achieved by a differential RNA splicing mechanism. Later on in development of B cell, regulation of RNA processing allows expressions of a membrane-bound form of IgD, again with same antigen-binding specificity Throughout this process, the same v region segment is being expressed with different C region segments." Class Switching Initially, all B cells matched to an antigen carry IgM specific for that antigen and produce IgM in response to this exposure to antigen. Later gene rearrangement permits elaboration of antibodies of same antigenic specificity but of different immunoglobulin classes. In class switching, the same assembled VH gene can sequentially associate with different CH gene, so immunoglobulin produced later (IgG, IgA or IgE) has the same specificity as original IgM but different biologic characteristics. Class switching is dependent on cytokines released from T cells and also happens after antigenic stimulation. Class switching is possible through a novel recombination event between repeat regions adjacent upstream of each constant heavy region class, the S regions