Interferon synthesis in x-irradiated animals. IV. Donor-type serum interferons in rat-to-mouse radiation chimeras injected with Newcastle disease virus.

C(3)H/He mice were exposed to total-body X-irradiation of 1000 roentgens and received thereafter 10(7) xenogeneic Wistar rat marrow cells intravenously. In these rat-to-mouse chimeras, serum interferon-producing capacity upon injection of Newcastle disease virus was examined four weeks after grafting. Normal levels of circulating interferon were produced. The interferon, however, had the species specificity of rat interferon, being 20 times more active in rat embryo fibroblasts than in mouse embryo fibroblasts. Moreover, it behaved like rat interferon when filtered on Sephadex G-100 dextran gel, displaying one peak of activity in the 90,000 molecular-weight range and two incompletely separated peaks of 32,000 and 24,000, respectively, in the 30,000 molecular-weight region. The fact that the interferon is of the donor type in rat-to-mouse chimeras permits us to conclude that circulating interferon induced by New-castle disease virus is made in bone-marrow-derived cells.