Monoclonal Antibodies to Mouse MHC Antigens. III. Hybridoma Antibodies Reacting to Antigens of the H-2b Haplotype Reveal Genetic Control of Isotype Expression

Eleven hybridoma antibodies directed against mouse major histocompatibility complex products of the H-2b haplotype have been produced and characterized. Of 7 antibodies reacting to H-2Kb and/or H-2Db antigens, all cross-reacted with other H-2 antigens, and 5 exhibited no correspondence with a known H-2 specificity established in the H-2 chart. Four anti-Iab antibodies all reacted with antigens encoded by the I-A subregion. Some of these antibodies showed no cross-reaction with other haplotypes, indicating reactions to private specificities of the I-Ab antigen. In addition, these anti-Ia antibodies appeared to be capable of distinguishing fine determinant differences, which corresponding alloantisera failed to reveal. A high frequency of hybridomas secreting IgM antibodies was found after fusions of spleen cells obtained from C3H anti-C3H.SW immunized mice, in contrast to the dominance of IgG hybridomas produced previously by fusions of spleen cells from mice immunized in the reverse direction. An isotype analysis of conventional cytotoxic alloantisera from the same strain combinations was therefore performed. The same correlation with respect to isotype expression was found, indicating that hybridoma antibodies reflect normal antibody responses and suggesting H-2-linked control of this expression.