Background

Class switch recombination (CSR) occurs during the normal maturation of B-cells. The initial step of CSR is the binding of an antigen to the B-cell surface-expressed immunoglobulin (Ig) H. Provided that the proper cytokines are present, antigen binding sets off a sequence of biological events that eventually lead to different mature B-cell populations each displaying or secreting antibodies of different classes. These classes reflect changes in the constant region of the antibody while the variable (antigen binding) region remains unaltered. The different classes of antibodies elicit differential interactions between host factors and the variable constant regions permitting the immune system to respond to the same antigen through distinct mechanisms. However, inducing CSR in vitro is time consuming, sometimes requiring