Alveolar macrophage--induced suppression of the immune response

Alveolar macrophages were shown to suppress the in vitro immune response of rabbit lymphoid cells stimulated with heterologous erythrocytes. Suppression was associated with an adherent, phagocytic cell that was resistant to the effects of irradiation and treatment with anti-thymus serum. Suppression was mediated by a soluble factor whose production was independent of antigen and required an interaction of viable alveolar macrophages and lymphocytes. Suppression was associated with an early event in the induction of the PFC response and appeared to affect lymphocyte proliferation. Suppression could not attributed to cytotoxicity, sequestration of antigen, depletion of nutrients or release of prostaglandins, arginase or thymidine. These results, taken together, provide additional information regarding immunological function of alveolar macrophages and suggest that they play a regulatory role in the immune response.