Differential activities of rabbit bone marrow suppressor cells.

A population of nonadherent Fc gamma-receptor-bearing (Fc gamma R+) suppressor cells in normal rabbit bone marrow (BM) which inhibited the constitutive proliferation of other BM cells has been previously described. Suppression was by blocking the release of a soluble growth-promoting factor. In the present report, it was found that the Fc gamma R+ BM suppressor cells, which were suppressive to background proliferation, were not suppressive to lymphocyte activation by immune complexes (IC). Adherent BM cells showed suppressive activity toward IC stimulation, but none toward constitutive BM proliferation. IC-induced proliferation was enhanced by the soluble growth factor, but only in the absence of adherent cells. Adherent cells did not affect growth factor enhancement of constitutive proliferation, suggesting that different cell populations were affected. Depletion of the Fc gamma R+ suppressor cells promoted growth of cells which subsequently developed Fc gamma R+, increasing the possibility of interaction with IC, which also preferentially induced Fc gamma R+ cells.