Characterization of lymphocytes which inhibit proliferation of human T cells exposed to lymphocyte-derived mitogenic factors.

Culture supernatants of PHA-activated human lymphocytes (active SUPs) contain factors which are strongly mitogenic for fractionated peripheral T cells. This stimulation is suppressed by certain non-T lymphocytes. It is shown that these suppressor cells can inhibit an ongoing response of T cells to active SUP and that this inhibition is reversible. Using various rosette sedimentation techniques for fractionating subpopulations of lymphocytes it is concluded that the suppressor cells lack membrane-associated receptors for C3 but possess receptors for the Fc part of IgG. This subset of lymphocytes may be an important regulator of lymphocyte proliferation during immune responses.