Insights into the B cell specific process of immunoglobulin class switch recombination

Antibody maturation leads to the formation of B cell receptors (BCRs) with high affinity for antigen and the production of different Ig isotypes. The different antibody isotypes vary in activities (half-life, binding to Fc receptors, ability to activate the complement system) and tissue localization and thus are necessary for an optimal humoral response against pathogens. The molecular mechanism responsible for exchanging the Ig isotypes (IgM to IgG, IgA, or IgE) and at the same time retaining the antigen specificity and affinity is called Ig class switch recombination (CSR). In this review we discuss the molecular mechanism of CSR, with special focus on the enzyme activation induced cytidine deaminase (AID).