Characterization of a p43 human thymocyte antigen

Two murine monoclonal antibodies (MoAbs), designated WM-25 and WM-35, have been prepared which react with human thymocyte cell surface membrane antigens. Both antigens were found to be expressed by normal and leukaemic immature human thymocytes. However, comparative examination by tissue section staining, immunoprecipitation, and electrophoresis, as well as competitive binding studies, demonstrated clear differences in the antigens detected by these two MoAbs. Antibody WM-35 identified a 48 kilodalton (kD) protein expressed on epidermal Langerhans cells as well as thymocytes, and appears similar to the previously reported Mabs OKT-6 and NA1-34. In contrast, MoAb WM-25 immunoprecipitated a 43 kD antigen, non-covalently associated with a 12 kD light chain, which was not present on Langerhans cells. Competitive binding and sequential immunoprecipitation studies confirmed that the 48 and 43 kD proteins are antigenically distinct. These results support the concept of at least two forms of thymocyte antigens within Cluster of Differentiation One (CD-1).