Identification of a tumor cell-derived differentiation antigen on mouse colony-forming units in the spleen and progenitor cells.

Surface membrane antigen(s) expressed on a mouse mast cell line (FMP1) have also been shown to occur on hemopoietic spleen colony-forming units (CFU-S) and granulocyte/macrophage colony- and erythroid burst-forming cells, using a xeno-antiserum raised against FMP1 cells. This mast cell model has been used to obtain antiserum and large quantities of antigen for the biochemical identification of CFU-S and progenitor cell antigen(s). Immunoprecipitation of FMP1 membrane antigens with the antiserum and subsequent polyacrylamide gel electrophoresis revealed the presence of five membrane proteins with molecular weights of 28,000, 32,000, 36,000, 50,000, and 70,000. Mouse B-lymphoma cell line W279 which reacted with anti-FMP1 serum was found to possess three immunoprecipitable surface proteins with molecular weights of 32,000, 50,000, and 70,000. Attempts have been made to identify the antigen(s) expressed by CFU-S and progenitors which were revealed by immunoprecipitation from the tumor lines. The three lower-molecular-weight proteins (Mr 28,000-36,000) were chosen for initial study. Membrane extracts of FMP1 cells were fractionated on Sephacryl S-200, and selective pools of these antigens were made. Antisera to these pools exhibited complement-dependent cytotoxicity to FMP1 cells, bone marrow CFU-S, granulocyte/macrophage colony-forming cells, and erythroid burst-forming units. These antisera immunoprecipitated Mr 28,000, 32,000, and 36,000 proteins from FMP1 cell membrane extracts but not the Mr 50,000 and 70,000 antigens. The W279 line has only one antigen (Mr 32,000) in the lower-molecular-weight range and is able to absorb anti-CFU-S and anti-progenitor activity, which suggests that it is this antigen which is expressed on hemopoietic cells. In addition, thymocytes react with anti-FMP1 serum, and the Mr 32,000 antigen was immunoprecipitated from thymus cell extracts. Binding studies with concanavalin A, wheat germ agglutinin, and lentil lectin indicated that the Mr 28,000-36,000 proteins were glycoproteins. The apparent molecular weights of these proteins on polyacrylamide gels were not altered by reduction and alkylation and therefore do not contain disulfide-linked subunits.