Helper T cells reacting to idiotype on IgG but not IgM

Immunization with an IgG1 but not an IgM monoclonal anti-NP (4-hydroxy-3-nitrophenyl acetyl) antibody induced idiotype-recognizing T helper cells, although these two antibodies carry the same variable regions. The T cells appear to react to an idiotype on the IgG1 but not the IgM antibody. They selectively enhance the expression of that idiotype in the IgG1 fraction of an in vitro anti-NP response.