Monoclonal xenogeneic antibodies to murine cell surface antigens: identification of novel leukocyte differentiation antigens

Abstract Hybrid myeloma cell lines secreting monoclonal antibodies to mouse cell surface antigens have been prepared. Spleen cells from a DA rat immunized with B10 mouse spleen cells that had been enriched for T cells were fused to cells from a nonsecreting mouse myeloma line (NSI). The presence in the culture supernatants of antibodies binding to mouse spleen cells was tested by a binding assay with 125 I‐labeled anti‐rat IgG. From a large number of positive cultures, ten independent hybrid clones were purified, each secreting a different antibody. Each antigenic target was analyzed by (a) gel electrophoresis of immunoprecipitated 125 I‐labeled cell surface molecules, (b) heat stability, (c) strain and species distribution and (d) cross‐inhibition of binding of different monoclonal antibodies. It was concluded that the ten monoclonal antibodies regognized four types of antigen. One was the heterophile, heat‐stable, Forssman antigen. The second (mol.wt. 210 000) appears to be a major 125 I‐labeled lymphoid cell surface protein. The third, a minor component of spleen cells, was precipitated as two polypeptides of mol.wt. 190 000 and 105000. Five IgG‐secreting clones identify the fourth antigen, a heat‐stable, possibly glycolipid component expressed on mouse red blood cells and also on thymocytes. Cross‐inhibition studies suggest that these last monoclonal antibodies bind to overlapping, but not identical, determinants. The class and chain composition of the monoclonal antibodies were studied by gel electrophoresis, isoelectric focusing and ability to lyse red blood cells and thymocytes.