Systemic interferon is produced by hematopoietic cells. (A) Irf7^−/− mice and WT mice were infected with VSV. IFN-α serum levels are shown (n = 2). (B) Irf7^−/− mice and WT mice were infected with LCMV. IFN-α serum levels are shown (n = 2). (C) WT mice were infected with VSV. After 10 hours, IFNa4, IFNb, and IFNk transcript levels were quantitated by RT-PCR (n = 3). (D) WT mice were infected with LCMV. After 10 hours, IFNa4, IFNb, and IFNk transcript levels were assessed by RT-PCR (n = 3). (E) WT mice were infected with VSV. After 10 hours, IRF7, USP18, and ISG15 transcript levels were assessed in the spleen by RT-PCR (n = 3). (F) WT mice were infected with LCMV. After 10 hours, IRF7, USP18, and ISG15 transcript levels were assessed in the spleen by RT-PCR (n = 3). (G-I) Bone marrow (BM) chimeras (WT-BM > WT, WT-BM > irf7^−/−, irf7^−/−-BM > WT and irf7^−/−-BM > irf7^−/− as described in “Methods”) were infected with VSV, n = 3-4 (G), LCMV, n = 4, (H), or HSV, n = 5 (I). IFN-α was measured in the serum.