IgG antibodies to phosphorylcholine exhibit more diversity than their IgM counterparts

An amino acid sequence analysis of the N-terminal immunoglobulin heavy and light chain variable regions (VH and VL) from 16 hybridoma proteins which bind phosphorylcholine as well as the complete sequence analysis of 9 of these VH regions is presented. There seem to be more VH regions participating in the phosphorylcholine response than can be encoded directly by germ-line VH gene segments. Moreover, the V regions from IgG antibodies are considerably more variable than those from their IgM counterparts. These observations raise the possibility that a somatic mechanism for V region diversification produces greater diversity in IgG than in IgM antibodies.