P. R. SÉKALY

Human T cells stimulated in secondary allogeneic mixed lymphocyte culture (MLC) were cloned under limiting conditions in microculture systems using T cell growth factor and irradiated allogeneic cells. Clones with lytic activity against either phytohemagglutinin-induced blast cells bearing the stimulating alloantigen(s) (cytotoxic T lymphocyte [CTL] activity), L1210 mouse lymphoma cells coated with rabbit antibody (antibody-dependent cell-mediated cytotoxicity [ADCC]), or K562 human target cells were selected, expanded, and then analyzed for different surface markers, including rosette formation with sheep erythrocytes (E rosettes), receptors for the fc portion of IgG or IgM (Fc gamma R and Fc mu R), and a group of antigens recognized by monoclonal antibodies including Ia, 4F2, OKT8,a nd OKT4. All the cytotoxic cells were E rosette+, Ia+ and 4f2+. Expression of Fc gamma R was restricted to the clones active in ADCC. CTL clones were either OKT8+ or OKT8-. Furthermore, three of the OKT8- CTL clones were OKT4+. In addition, some cytolytic clones devoid of specific CTL activity were OKT8+. It thus appears that the claim that human CTL are OKT8+, OKT4-, and Ia- is not supported by the analysis of their phenotype at the clonal level.

Receptors for the Fc portion of immunoglobulin G (Fc gamma R) on the surface of human peripheral T cells can be modulated on contact with antigen-antibody immune complexes (IgG-IC). Our results demonstrate that the Fc gamma R present on the surface of human B cells are also modulated on exposure to IgG-IC. Furthermore, the expression of HLA-DR molecules is not affected by the IgG-IC induced disappearance of Fc gamma R. In fact, the percentage of HLA-DR-positive cells and the relative amount of HLA-DR molecules on individual B cells analysed by flow microfluorometry was shown not to be influenced by Fc gamma R modulation. Moreover, pretreatment of cells with monoclonal antibodies directed against non-polymorphic determinants of HLA-DR antigens did not prevent the binding of IgG-coated ox erythrocytes. These results argue against a structural relationship between Fc gamma R and HLA-DR molecules on the surface of the B-cell populations investigated here.