Surface receptors and immune activity of purified human circulating mononuclear cells: IV. The demonstration of seven subclasses of T cells in the circulation of the normal individual: The cytotoxic activities of these cells

Abstract

T lymphocytes were isolated from monocyte-depleted mononuclear cells of normal individuals by rosetting them with sheep erythrocytes. These purified T cells were preferentially depleted of cells with receptors for FcG (T G cells), FcM (T M cells), or C3 (T C cells) by rosette formation with EA(G), EA(M), and EAC, respectively, before or after incubation for 24 hr in medium 199 fortified with fetal calf serum (20%). The unfractionated lymphocytes and the purified and the depleted T cells were analyzed for receptors to FcG, FcM, and C3 and for cytotoxic activity in the natural killer (NK), antibody dependent cell-mediated cytotoxicity (ADCC), and mitogen-induced cell-mediated cytotoxicity (MICC) assays. The T G and T C cells were detected among the freshly isolated T cells, whereas the T M cells were detected only following 24 hr of incubation. Removal of T C cells from the 24-hr-cultured T cells resulted in removal of all the T C cells and in the concomitant removal of the majority of T M cells. Similarly, removal of T M cells from the 24-hr-cultured T cells resulted in the elimination of all T M cells as well as the majority of T C cells. These results demonstrate the in vitro generation of T cells with receptors for both FcM and C3 (T M+C cells). Ten percent of the freshly isolated T G cells possessed detectable receptors for C3 and/or FcM. These cells constitute the T G+C and T G+M lymphocytes. Support for consideration of these receptor-bearing cells as unique and stable cells is provided by the finding that T M and T C cells maintained in culture for up to 72 hr do not generate other receptors but retain the single receptor which characterizes each of these cells. Only a small percentage of cultured T G cells generate receptors for C3 and FcM. It may therefore be concluded that the T G, T M, and T C cells are stable unireceptor-bearing cells. The T G, T M, T C, T G+C, T G+M, and T M+C lymphocytes account for approximately 50% of the circulating lymphocytes. Whether the remaining cells, the T null or T N cells, constitute the precursors for any or all of the receptor-bearing T cells remains to be determined. Unfractionated freshly isolated T cells were highly cytotoxic in the NK and PWM-mediated MICC assays but were relatively inactive in the ADCC, naturally occurring cell-mediated cytotoxicity (NOCC), and PHA- and Con-A-mediated MICC assays. In contradistinction, T cells incubated for 24 hr displayed marked cytotoxic activity in the ADCC and PHA-mediated MICC assays; they were inactive in the NOCC and Con-Amediated MICC assays. The T G cells were the predominant cytotoxic cells in the ADCC, NK, and MICC cytotoxic assays since their selective elimination from either the freshly isolated or 24-hr-incubated T cells resulted in almost total loss of cytotoxic activity of the remaining cells. Removal of the T G+C cells from the freshly isolated or 24-hr-incubated T cells resulted in a significant decrease in PHA- and PWM-mediated MICC cytotoxic activity. T cells depleted of T M, T M+C, and T C cells exhibited the same cytotoxic activity as did the unfractionated T cells. These results suggest that the predominant cytotoxic T cells in all the assays investigated are the T G cells, that limited cytotoxic activity is also displayed by the T G+C cells, and that the T M, T M+C, T C, and T N cells display no cytotoxic activity in the assays utilized in this investigation.