Characterization of plasma membrane proteins identified by monoclonal antibodies

Monoclonal antibodies that react with antigens of the plasma membrane have been prepared by fusion of mouse myeloma cells and spleen cells of rats immunized with NIH/3T3 cells or plasma membranes. The antigenic targets of these antibodies included three major cell membrane proteins of 100, 90, and 80 kilodaltons. Proteins of 220, 71, and 55 kilodaltons were also specifically immunoprecipitated. Characterization of the antigens by treatment with proteases, heat, and acetone extraction provided additional evidence that the reactive molecules were proteins. The 90- and 80-kilodalton proteins were preferred targets in this experimental system; of 13 independent monoclonal antibodies which were characterized, four reacted with the 90,000-dalton protein and two with the 80,000-dalton protein. The expression of these antigens in different types of cells was tested with a panel of murine cell lines. The 220- and 90-kilodalton proteins were present on 18 lines of diverse tissue and strain origin and may be structural components common to plasma membranes of many cell types. The other protein antigens were reduced or modified on many cells other than the fibroblast, indicating that the expression of these antigenic determinants of the 80,000-dalton protein were absent in cells of several murine inbred strains, suggesting that this protein was expressed by a polymorphic gene(s).