Three distinct epitopes of the human MSK20 cell surface antigen are expressed on human and nonhuman primate cells.

Five monoclonal antibodies which indirectly agglutinate human rbc were isolated and designated 2D8, 4E12, 4H10, 5A8, and 5H5. Expression of the antigen defined by 2D8 was 100% concordant with the presence of human chromosome 19 in a panel of human-Chinese hamster somatic cell hybrids. Secondary clones isolated from antigen positive hybrids exposed to antibody 2D8 and complement were shown to have lost both the cell surface antigen and chromosome 19. Small terminal deletions of 19p were observed in the karyotypes of two antigen negative clones that continued to express human GPI. All five monoclonal antibodies and the previously isolated F10 labelled the surface of parental cells and did not label the surface of deletion mutants, and the five monoclonal antibodies produced in this study inhibited the binding of F10 to the human rbc surface. Therefore, all must recognize the MSK20 cell surface antigen which was defined previously by antibody F10. Chimpanzee cells bind 5A8 and 5H5, orangutan cells bind 4E12, and neither bind 2D8 and 4H10. Therefore, the monoclonal antibodies produced in this study must recognize at least three distinct epitopes of the MSK20 cell surface antigen which are expressed on the human rbc.