Monoclonal Antibodies to Mouse Major Histocompatibility Complex Antigens

As part of our continuing effort to produce a library of hybridoma antibodies specific for the products of the mouse major histocompatibility complex (MHC), nine antibodies reacting with antigens of the H-2d haplotype have been produced by cell fusion between immune spleen cells and the SP2/0.Ag.14 cell, of H-2d origin. Serological characterization revealed that seven antibodies reacted with H-2 antigens and two with Ia antigens. Of the anti-H-2 antibodies, four detected private specificities of H-2Kd or H-2Dd antigens and three detected public specificities of H-2d and other haplotypes. One of the anti-Ia antibodies detected a private Ia specificity corresponding to Ia.23 and the other detected a previously undescribed public specificity. Anti-H-2d hybridoma cells represent a potential "autoreactive" situation in that the antibodies produced by the cells should react with their own H-2 antigens unless expression of the corresponding H-2d antigens in these cells was altered. In order to examine whether H-2d antigens continued to be expressed on these anti-H-2d hybridoma cells, binding of 125I-labeled monoclonal anti-H-2Kd and/or H-2Dd antibodies was studied. Among the four hybridoma clones tested, three bound specifically three independent 125I-labeled anti-H-2d antibodies, including two cases in which binding of autologous antibodies was detected. The last clone did not bind any of the anti-H-2d antibodies, although it bound an anti-H-2k antibody, indicating selective loss of H-2d antigens. These observations demonstrate that neither loss nor retention of H-2d antigen expression on the cell surface is obligatory in hybridoma cells producing anti-H-2d antibodies.