Ig Isotyping

In immunology, the immunoglobulin (Ig) isotype (class) is encoded by the constant region segments of the immunoglobulin gene which form the Fc (Fragment crystallizable region) portion of an antibody. The expression of a specific isotype determines the function of an antibody via the specific binding to Fc receptor molecules on different immune effector cells. Isotype expression reflects the maturation stage of a B cell. Naive B cells express IgM and IgD isotypes with unmutated variable genes, which are produced from the same initial transcript following alternative splicing. Expression of other antibody isotypes (IgD, IgM IgG1-4, IgA1-2, IgE) occurs via a process of class-switch recombination (CSR) after antigen exposure. Class-switching is mediated by the AID (activation-induced cytidine deaminase) enzyme and only occurs after the B cell binds an antigen through its B cell receptor, and is further activated through interaction with a T helper cell.

Immunoglobulin isotype