Comparison of the allotypic combining sites on H-chains of rabbit IgG and IgM

Abstract

Allotypic markers originally found on rabbit IgG have been shown to reside also on both the heavy and light chains of rabbit IgM. The light chains of IgG and IgM are the same, but the heavy chains of these two immunoglobulins differ extensively. The extent to which the allotypes present on the heavy chains are duplicated on the two immunoglobulins has been investigated by inhibition of phage neutralization and by a radiotracer technique. The inhibition by anti-allotype sera of phage neutralization by IgM antibody was shown to be essentially completely removed by prior absorption of the anti-allotype sera with IgG of the same heavy chain allotype. A preparation of IgM containing allotype a1 exhausted extensively but not completely, the precipitating ability of anti-a1 serum for a1, b4 IgG labeled with I 125. It is concluded that in the anti-allotype sera investigated, essentially all of the antibodies directed against the allotypic sites present on IgM react with IgG, but not all the antibodies directed against the allotypic sites present on IgG are capable of reacting with IgM. The implications of these findings with regard to the genetic control of immunoglobulin synthesis and the evolution of the immunoglobulin genome are discussed.