Murine cell surface glycoproteins. Characterization of a major component of 80,000 daltons as a polymorphic differentiation antigen of mesenchymal cells.

Monoclonal antibodies reactive with NIH/3T3 cell surface antigens were obtained from hybridomas of murine myeloma cells fused to spleen cells of rats immunized with NIH/3T3 cell plasma membranes. Four of the antibodies, of forty that have been studied, appeared to react with allospecific antigenic determinants: they bound to NIH/3T3 cells but not to BALB/ 3T3 cells. Each of these four antibodies immunoprecipitated a glycoprotein of about 80,000 daltons that migrated to an isoelectric point of about pH 5.0. Polypeptides of identical molecular weight and isoelectric points, and yielding the same proteolytic cleavage fragments, were present in BALB/3T3 cells, but were not antigenically reactive. The 80,000-dalton glycoprotein was a major constituent of the plasma membrane. It was a predominant lactoperoxidase iodinated component of intact NIH/3T3 cells, and saturation binding of 125I-labeled antibody indicated that there were about 10(6) antigenic sites/cell. Studies of the distribution of the immunoreactive glycoprotein among different strains of mice confirmed the polymorphic expression of the determinant: Spleen cells of BALB/c, DBA/1, DBA/2, and CBA mice did not bind anti-80,000-dalton glycoprotein monoclonal antibodies, whereas spleen cells of a large number of other strains of mice were positive for antibody-binding. The antigenic reactivity varied markedly among different cell lines and was greatest with the NIH/3T3 mouse embryo fibroblast, G8-1 Swiss Webster myoblast, and IC-21 SV40-transformed C57BL/6 mouse peritoneal macrophage. The properties of the 80,000-dalton glycoprotein characterized this molecule as a new cell surface differentiation alloantigen of murine mesenchymal cells.