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 (ยต), 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. But the antigen specificity of the antibody remains the same because the N-terminal of the H chain remains unchanged (as does the entire L chain). Class switch recombination enables the body to produce antibodies with different effector functions; that is, different means of dealing with the same antigen. The ability of a B cell to switch CH gene segments depends on its receiving help from helper T cells.
