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 blastogenesis 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 lymphoprolifrative 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 proportion of macrophages ordinarily present in spleen of normal, unstimulated chickens. This heretofore unrecognized suppressive capability of normal, presumably resting macrophages have been detected in certain infections.