Class switch recombination (CSR) - Cuntorio

As B cells grow into a clone in response to antigen, they may rearrange their DNA once again. For example, a B cell that has assembled a complete gene for the H chain of IgM (µ), may cut the gene on the 3´ side of the assembled V-region segments and move the assembly to the 5´ side of another of its CH gene segments. Now the cell begins to make a different class of antibody, such as IgG or IgA.