title: Regulation of human T lymphocyte mitogenesis by antibodies to CD3.
abstract: The inhibitory and mitogenic effects of anti-CD3 antibodies (anti-CD3) were examined in cultures of human peripheral blood T cells. Resting T cells required the presence of accessory cells (AC) or phorbol myristate acetate (PMA) to be stimulated by soluble anti-CD3 (OKT3 and 64.1). Anti-CD3 was unable to induce activation of AC-depleted T cells as determined by IL 2 receptor expression, IL 2 production, cell cycle analysis, or detectable DNA synthesis. Although T cell responses to PHA also required AC, far fewer were necessary to generate responses. Anti-CD3 inhibited PHA-stimulated T cell IL 2 production, IL 2 receptor expression and proliferation in partially AC-depleted cultures. Moreover, anti-CD3 was able to inhibit PHA responses when added to culture as late as 24 to 42 hr after the initiation of a 96-hr incubation. Increasing concentrations of PHA reduced the inhibitory effect of anti-CD3 on PHA-stimulated T cell proliferation, whereas IL 2 production remained suppressed. Anti-CD3 linked to Sepharose beads effectively inhibited PHA-stimulated T cell DNA synthesis, indicating that internalization of the CD3 molecule was not required for inhibition of PHA responses. Although inhibition of IL 2 production was a major effect of anti-CD3 in PHA-stimulated cultures, it was not the only apparent inhibitory effect because the addition of exogenous IL 2 could not prevent inhibition completely. Intact AC but not IL 1 also reduced anti-CD3-mediated inhibition of PHA responsiveness, whereas the addition of both IL 2 and AC largely prevented inhibition. Thus, anti-CD3 in the absence of adequate AC signals exerted a number of distinct inhibitory effects on mitogen-induced T cell activation. These results suggest that the CD3 molecular complex may play a role in regulating T cell responsiveness after engagement of the T cell receptor by a number of mechanisms, some of which involve inhibition of IL 2 production.
mesh_terms: D000906:Antibodies / Q000276:immunology*; D000945:Antigens, Differentiation, T-Lymphocyte; D000954:Antigens, Surface / Q000276:immunology*; D002478:Cells, Cultured; D004261:DNA Replication; D006801:Humans; D007375:Interleukin-1 / Q000494:pharmacology; D007700:Kinetics; D010835:Phytohemagglutinins / Q000037:antagonists & inhibitors / Q000494:pharmacology; D011994:Recombinant Proteins / Q000494:pharmacology; D013601:T-Lymphocytes / Q000187:drug effects / Q000276:immunology*
chemical_list: D000906:Antibodies; D000945:Antigens, Differentiation, T-Lymphocyte; D000954:Antigens, Surface; D007375:Interleukin-1; D010835:Phytohemagglutinins; D011994:Recombinant Proteins