Clones producing antibodies of more than one class

Clones producing antibodies directed against oligo-D-alanine (D-ala) determinants have been demonstrated in X-irradiated recipient mice after transfer of limited numbers of spleen and thymus cells. Seven out of eighty-one recipients were found to have donor allotype clones, all of which produced IgG1 antibodies to D-ala; two of these clones also produced small quantities of IgG2a antibodies. In addition, each of the seven responder mice contained IgM antibodies to D-ala. Isoelectric focusing (IEF) patterns of anti-D-ala antibodies from each of the seven responder mice were restricted and compatible with one to three antibody types. Most of these IEF patterns were significiantly different from each other. Five mice have been used for a comparison of IgM and IgG1 combining sites by affinity and specifity measurements. In each case affinity and specificity of IgM and IgG1 antibodies were alike. No similarity was found when comparing IgM from one clone with IgG1 from another one. These data led us to conclude that a single precursor cell can give rise to a clone producing antibodies of the IgM class and different IgG subclasses all of which share combininig sites.