Human peripheral T lymphocytes may be identified and isolated by their ability to form rosettes with sheep erythrocytes. Moretta and colleagues (1) further defined subclasses of T lymphocytes based upon the presence of receptors for the Fc portion of IgM (Tp cells) 2 or IgG (Ty cells). Monoclonal antibodies that detect specific cell surface antigens provide another method to define lymphocyte subsets. Recently, Reinherz et a/.(2), and Kay and Horwitz (3) have compared the subsets of T lymphocytes defined by Fc receptors or reactivity with monoclonal antibodies and suggested that Ty cells may not be of T cell lineage. We report here a more definitive characterization of Ty cells with a panel of monoclonal antibodies that recognize additional antigens on T cells. We demonstrate that although some Ty cells may lack 1 T lymphocyteassociated antigen (OKT3), they do bear other antigens characteristic of T cells. We conclude from these data that Ty cells are T lymphocytes.

The monoclonal antibodies used in this study included antibody SCl (4), which immunoprecipitates the same molecule as does L17F12 (5) or OKTl (6). Antibodies OKT3, OKT4, OKT8. and OKMl were provided by Dr. Patrick Kung (Ortho Pharmaceutical Research, Raritan, NJ) and have been previously described (2, 6, 7). Antibody 9.6, which identifies a T lymphocyte surface protein associated with the E-rosette receptor (81, was a gift from Dr. J. Hansen (Hutchinson Cancer Research Center, Seattle, WA). Antibody 3A1 was a gift from Dr. A. Fauci of the National Institutes of Health (9). and antibody T305 was generously provided by Dr. I. Royston of the University of California, San Diego. Peripheral blood lymphocytes (PBL) were isolated from heparinized venous blood by dextran sedimentation, carbonyl iron treatment to remove monocytes, and Ficoll-Hypaque density gradient centrifugation as previously described (1 0). Sheep erythrocyte rosetting (EN+) lymphocytes were isolated by incubating PBL with neuraminidase-treated sheep erythrocytes followed by Ficoll-Hypaque density gradient centrifugation. Monocytes were isolated from peripheral blood mononuclear cells by adherence to plastic, followed by elution with 0.01 M EDTA plus gentle scraping and were> 95% esterase positive. The Ty subpopulation was obtained by rosetting EN+ cells with IgG-coated bovine erythrocytes, followed by Ficoll-Hypaque gradient purification as previously described (1 l), and contained less than 2% esterase-staining cells. Ty-lymphocytes failed to rosette with IgG-coated bovine erythrocytes and were isolated from the interface of the Ficoll-Hypaque gradient. For immunofluorescent staining, 1 O6 mononuclear Cells were incubated with the specific monoclonal antibody or a control myeloma protein at 4 C in the presence of 10” M sodium azide followed by fluorescent goat F (ab% anti-mouse lg, as previously described (1 2). The stained cells were analyzed by using a FACS