Role of cellular proliferation in the stimulation of MPS phagocytic activity.

Administration of agents such as stilboestrol, endotoxin, C. parvum and zymosan, which enhance the phagocytic activity of the mononuclear phagocyte system, also stimulated cellular proliferation in the liver and spleen as assessed by [13H] thymidine incorporation into these organs, and by autoradiography and the number of mitoses in the liver. Sublethal whole body irradiation abolished the proliferative response to stimulation and also reduced or prevented the increase in phagocytic activity. This latter effect depended on the stimulatory agent used, dose of radiation and time of irradiation with respect to stimulation. The results indicate that cell proliferation is important for the increase in phagocytic activity after administration of C. parvum, zymosan and stilboestrol. Endotoxin, however, appears to act primarily by increasing the capacity of existing cells while at the same time causing cell proliferation. The population of cells responding to zymosan by increased phagocytic activity through proliferation was shown to be resident in the liver.