DNL 1.9: a monoclonal antibody which specifically detects all murine B lineage cells

A rat anti-mouse monoclonal antibody, DNL 1.9, has been produced and shown to bind to all cells of the B lineage in mice. By quantitative immunofluorescence, DNL 1.9 binds to approximately 50% of spleen cells, 20-30% of lymph node cells, but no to thymocytes. In bone marrow and neonatal liver, 70-80% of the small cells and 10-20% of the large cells were identified by this antibody. Two-color immunofluorescence studies showed that all immunoglobulin-positive cells were also DNL 1.9-positive, while Thy-1.2-positive cells did not bind the monoclonal antibody. All pre-B cells in bone marrow , as identified by cytoplasmic IgM staining, were labeled by the DNL 1.9 antibody. A significant proportion of lymphocytes in the bone marrow which did not express cell surface immunoglobulin did bind DNL 1.9. Both direct and indirect plaque-forming cells were also shown to bind DNL 1.9 antibody. The antigen recognized by this monoclonal antibody was not immunoglobulin nor was the antigen present in normal mouse serum. All seven mouse strains tested showed similar patterns of antigen expression. These results show that all of the cells indentifiable as being of the B lineage were identified by this monoclonal antibody. It is possible that the cells which bind DNL 1.9 but do not express cell surface immunoglobulin may be very early precursors of B lymphocytes.