Interferon preparations enhance phagocytosis in vivo

Previous studies have shown that interferon (IF) preparations enhance phagocytic activity in cultured mouse peritoneal macrophages. It is shown here that cell culture fluids containing large amounts of IF, which had been treated with acid and clarified of the inducer, Newcastle disease virus, enhanced phagocytic activity when injected into mice. Enhanced phagocytic activity also was observed after injection of Newcastle disease virus into mice, but the contribution of IF to this event was unclear. The kinetics of the phagocytic response to inducers in vivo were biphasic. Depression of phagocytosis occurred around 16 to 18 h after injection of Newcastle disease virus. The observed enhancement began about 12 h later and lasted for at least 60 h more. It was concluded that the complexity of the response of mice to an inducer makes analysis of the role of IF in the ensuing events difficult. However, because of documented phagocytosis-enhancing effects of IF in vitro, it is very likely that the in vivo effects observed here are to some degree mediated by IF. On this basis, the concept of the activity of IF as a lymphokine is potentially expanded.