In vitro suppression of T-cell mitogenic response and tumor cell proliferation by spleen macrophages from normal chickens

Adherent cells isolated from spleen of normal specific pathogen-free chickens inhibited mitogen-induced lastogenesis of autochthonous, syngeneic, or allogeneic lymphocytes. The adherent cells were also inhibitory to in vitro proliferation of cells of a rapidly dividing tumor line, MDCC-MSB-1, derived from a lymphoma induced by Marek's disease virus. The effector cell of suppression of both lymphoproliferative functions appeared to be a macrophage because the suppressive activity of adherent cells could be abrogated by pretreatment with carrageenan but not with antisera specific to chicken T or B cells. The proportion of macrophages needed for effective suppression was substantially higher than the porportion of macrophages ordinarily pesent in spleen of normal, unstimulated chickens. This heretofore unrecognized suppressive capability of normal, presumably resting macrophages in chickens needs to be evaluated in light of the fact that suppressor macrophages have been detected in certain infections.