Human lymphocyte markers defined by antibodies derived from somatic cell hybrids. IV. A monoclonal antibody reacting specifically with a subpopulation of human B lymphocytes.

The technique of somatic cell hybridization has been used to produce a monoclonal antibody (designated FMC7) against the human B lymphoblastoid cell line HRIK. By indirect immunofluorescence FMC7 reacted with a total of 3 out of 10 B cell lines, but failed to bind T and Null cell lines. On normal peripheral blood, FMC7 bound between 3 and 6% of mononuclear cells. When normal peripheral blood mononuclear cells were fractionated, FMC7 reacted with only the B-enriched fraction, staining some but not all cells expressing SMIg. Double marker analysis indicated that the antigen detected by FMC7 is not identical with any of the conventional B cell markers, including surface membrane IgM, C3 receptors, Fc receptors, and the binding site for mouse erythrocytes. Another monoclonal antibody, FMC1, which reacts specifically with B lymphocytes, binds a separate antigenic determinant. Thus, FMC7 appears to recognize a previously undetected marker present specifically on a subpopulation of human B lymphocytes. FMC7 reacts with some but not all B cell leukemias and may have diagnostic applications in leukemia.