Effector activity of OKT4⁺ and OKT8⁺ T-cell subsets in lectin-dependent cell-mediated cytotoxicity against adherent HEp-2 cells

Abstract

The role of OKT4⁺ and OKT8⁺ T-cell subsets was studied in lectin-dependent cell-mediated cytotoxicity (LDCC) against adherent HEp-2 human epipharynx carcinoma target cells. LDCC was evaluated by detachment from the monolayer of [³H]thymidine prelabeled HEp-2 cells in a 24-hr assay with a concanavalin A (Con A) dose of 25 μg/ml at effectortarget cell ratios of 5:1, 25:1, and 50:1. Under these conditions but without Con A considerable natural cell-mediated cytotoxicity (NCMC) was not elicited; however, the cytotoxicity was significantly augmented in the presence of Con A (=LDCC) by sheep erythrocyte rosette-forming T lymphocytes and by both OKT4⁺ and OKT8⁺ T-cell fractions. LDCC activity by isolated OKT8⁺ T cells was superior to that by OKT4⁺ T cells and unfractionated T lymphocytes. By contrast, addition of either OKT4⁺ or OKT8⁺ T cells together with unfractionated T lymphocytes, or OKT4⁺ and OKT8⁺ T cells mixed at ratios of 1:1, 1:2, and 2:1, to target cells did not result in major differences in comparison of LDCC activities by these mixed effector cell populations with each other or with that by unfractionated T lymphocytes. Parallel studies were carried out to determine the effect of OKT4⁺ and OKT8⁺ T-cell subsets on the Con A-induced proliferation of peripheral blood mononuclear cells (PBMC). While OKT8⁺ T cells inhibited the mitogenic response to Con A, OKT4⁺ T lymphocytes had no major effect. A higher responsiveness of the OKT8⁺ to OKT4⁺ T-cell subset in LDCC to HEp-2 targets and in Con A-induced lymphocyte proliferation is suggested.