Regulation of lymphocyte responses in vitro, : V. Suppressor activity of adherent and nonadherent rat lymphoid cells

Abstract

Normal rat spleen cell synthesis of DNA in response to stimulation with PHA is inhibited at high doses of PHA (≥ 1 μliter/ml) and with cell concentrations ≥ 10 6/ml. Inhibition is removed when the subpopulation adherent to glass wool is removed and is not restored by reconstituting with purified splenic or peritoneal macrophages. Since the inhibitory or “suppressor” cells do not adhere to plasic and can be recovered from glass wool by simple agitation, they are considered to be weakly adherent spleen cells. Removal of suppressor cells on glass wool does not affect the time course of DNA synthesis by the remaining cells in response to PHA; the peak at 2–3 days is followed by the usual rapid fall to low levels by the fifth day. Spleen cells exert suppressor activity on lymph node cells, in mixtures stimulated with moderate doses of PHA. A new hypothesis, based on a comparison of the present results with recent findings in other laboratories, is proposed: that the regulatory unit in spleen is a suppressor T-cell-macrophage complex.