Inhibitory effect of human mononuclear phagocytes on DNA synthesis in stimulated lymphocytes.

Human mononuclear phagocytes cultured in vitro revealed an inhibitory influence on DNA synthesis, as measured by 3H thymidine incorporation, in lymphocytes stimulated by a lectin (PHA), a soluble antigen (PPD) and allogenic lymphocytes. The inhibitory effect increased with increasing ratio of macrophages to lymphocytes, and was positively related to the differentiation of monocytes to macrophages. The inhibitory ability appeared to have no connection with the histocompatibility gene complex. The culture medium of macrophages cultured with and without lymphocytes showed no inhibitory effect.