Thy‐1 is a differentiation antigen that characterizes immature murine erythroid and myeloid hematopoietic progenitors

To determine the role of Thy‐1 antigen in murine hematopoietic differentiation, bone marrow was treated with anti‐Thy‐1.2 antibody and complement or complement alone. Growth of immature hematopoietic progenitors, erythroid burst‐forming units (BFU‐E), and granulocyte/macrophage colony‐forming units (CFU‐GM) was greatly reduced following antibody and complement treatment and was not restored by mitogen‐stimulated spleen cell supernatants. In contrast, more mature erythroid and myeloid progenitors, the erythroid colony‐forming unit (CFU‐E) and the macrophage progenitor stimulated by L‐cell‐conditioned media (LCM), were spared by anti‐Thy‐1.2 antibody and complement treatment. Here, to separate the effects of anti‐Thy‐1.2 antibody treatment on accessory cells from those on progenitors, splenic T cells and thymocytes were added to treated marrow at ratios of up to 200%. Growth of BFU‐E and CFU‐GM was not restored. To more precisely replace required accessory cells, male complement‐treated marrow was cocultured with female anti‐Thy‐1.2 antibody and complement‐treated marrow. Even marrow cells failed to restore female BFU‐E and CFU‐GM growth. Fluorescent‐activated cell sorting (FACS) and immune sheep red cell rosetting with anti‐Thy‐1.2‐labeled marrow were then performed to determine if immature hematopoietic progenitors bear Thy‐1.2‐positive fraction, demonstrating the presence of Thy‐1.2 on early murine hematopoietic progenitors. CFU‐E and CFU‐M were present in the Thy‐1.2‐negative fraction following FACS separation. These data demonstrate that Thy‐1.2 is a differentiation antigen, present on at least some murine BFU‐E and CFU‐GM and lost as they mature to CFU‐E and CFU‐M.