Interferon Synthesis in X-Irradiated Animals V. Origin of Mouse Serum Interferon Induced by Polyinosinic-Polycytidylic Acid and Encephalomyocarditis Virus

Abstract

The radioresistant cell systems producing serum interferon after intravenous administration of polyinosinic-polycytidylic acid [poly(I·C)] or encephalomyocarditis virus in mice were studied in rat-to-mouse radiation chimeras. Interferon induced by poly(I·C) became of donor type within 3 months after grafting of irradiated C3H/He mice with Wistar rat bone marrow cells; this indicated that it was made in cells derived from the hemopoietic system. In contrast, encephalomyocarditis virus-induced interferon remained of recipient type in xenogeneic chimeras up to 3 months after grafting, which indicated that the bulk of this interferon originated from a cell population not derived from the hemopoietic system. To ascertain that the respective radiosensitivities of the systems producing rat interferon in chimeras corresponded to that of normal mice, some rat-to-mouse chimeras were subjected to a second X irradiation 1 month after the first irradiation and restoration. Circulating interferon production was studied 4 days later. As expected, the re-irradiation strongly depressed rat serum interferon production induced by Newcastle disease virus but had no effect on rat interferon synthesis induced by poly (I·C). These results point to a macrophage origin for the bulk of poly(I·C)-induced circulating interferon.