Thy-1 antigen in murine hematopoietic progenitor differentiation.

Until recently, the presence of Thy-1 antigen was thought to identify thymus-derived lymphocytes as opposed to other lymphohematopoietic cells. With the use of a highly amplified immunofluorescence assay and a monoclonal anti-Thy-1 antibody, the Thy-1 antigen has been detected on CFU-S. To determine the role of Thy-1 antigen in the differentiation of more committed hematopoietic progenitors, murine bone marrow was treated with anti-Thy-1.2 antibody and complement and cultured. Growth of erythroid burst-forming units (BFU-E) and granulocyte/macrophage colony-forming units (CFU-G/M) was greatly reduced following antibody and complement treatment and could not be restored with mitogen-stimulated spleen cell supernatants, splenic T cells, or thymocytes. These data demonstrate that a Thy-1.2-bearing cell is important in differentiation of early murine hematopoietic progenitors and they provide evidence that anti-Thy-1.2 antibody and complement treatment removes Thy-1.2 antigen-bearing hematopoietic progenitors. In contrast, growth of the macrophage progenitor (CFU-M) stimulated by L cell-conditioned media and the more mature erythroid colony-forming unit (CFU-E) was unaffected by anti-Thy-1.2 antibody and complement treatment. Therefore, Thy-1.2 antigen is not present on these progenitors. These data suggest that Thy-1.2 antigen is a differentiation antigen that is present on early murine hematopoietic progenitors and is lost as they differentiate.