isotype switching

The switch of immunoglobulin isotype that occurs, for example, when the immune response progresses (IgM to IgG). The switch from IgM to IgG involves only the constant region of the heavy chains (from m to g ), the light chain and variable regions of the heavy chain remaining the same, and involves the switch regions, upstream (on the 5\' side) of the constant region genes, at which recombination occurs. Similarly, IgM and IgD with the same variable region of the heavy chain, but with different heavy chain constant regions ( m and d ), seem to coexist on the surface of some lymphocytes.