EXPRESSION OF THE CMRF-35 ANTIGEN, A NEW MEMBER OF THE IMMUNOGLOBULINGENE SUPERFAMILY, IS DIFFERENTIALLY REGULATED ON LEUKOCYTES

A new monoclonal antibody, CMRF-35, has been generated that recognized a 224 amino acid cell surface protein which is a novel member of the immunoglobulin gene superfamily. The antibody, raised against large gr anular lymphocytes (LGL), stains LGL, monocytes, macrophages and granu locytes but not platelets or erythrocytes. In addition, a subset of pe ripheral blood T lymphocytes (26.6 +/- 13.4% CD5+ cells) and B lymphoc ytes (13.7 +/- 6.8% CD20+ cells) stained with CMRF-35 but tonsil T and B cells were essentially negative. Expression of the CMRF-35 antigen (Ag) on different leucocyte populations was markedly influenced by sti mulation of the cells with mitogens and cytokines. Activation of perip heral blood T cells with phytohaemagglutinin (PHA), or phorbol myrista te acetate (PMA) and calcium ionophore (CaI) led to a decrease in the proportion of CMRF-35+ T lymphocytes. In contrast, PHA activation of t onsil T lymphocytes resulted in an increase in CMRF-35 Ag expression ( 47.1 +/- 1.5% CD5 cells at 6 days). An increase in CMRF-35 Ag was also seen on phorbol ester and CaI-activated tonsil B cells. No change in CMRF-35 expression on natural killer (NK) cells occurred following act ivation with interleukin-2 (IL-2) but the CMRF-35 Ag was down-regulate d following Fc receptor stimulation. A moderate increase in CMRF-35 ex pression occurred during monocyte-macrophage differentiation and the e xpression of the Ag on monocytes was differentially regulated by inter feron-gamma (IFN-gamma). This regulation of the CMRF-35 Ag on the leuc ocyte surface suggests that the molecule has an important function com mon to diverse leucocyte types.