Macrophages as effectors of T suppression: T-lymphocyte-dependent macrophage-mediated suppression of mitogen-induced blastogenesis in the rat

Small numbers of appropriately stimulated (but not resident) peritoneal macrophages in the rat are shown to inhibit mitogen induced lymphocyte proliferation. A variety of in vivo and in vitro cell selection/fractionation procedures applied to the indicator (lymphocyte) population indicates that the cytostatic potential of the macrophages is not expressed spontaneously in vitro, but is dependent upon the activity of a second “regulator” cell from the lymphocyte population. The latter cell is shown to be large, long lived, and recirculating, highly sensitive to anti-thymocyte serum and cyclophosphamide, insensitive to irradiation, indomethacin, and mitomycin C, adherent to glass wool, and to survive poorly in culture—it is most active in vivo in the early neonatal period, contributing significantly to the lack of demonstrable PHA-responsiveness in splenocyte cultures from new born rats. A similar cell (nominal suppressor T cell) is shown to appear in lymph nodes during primary immune responses to soluble antigen.