Therefore, we selected Irf7 (Interferon regulatory factor 7) to generate knock-out mice on a C57BL/6J background by backcrossing and to investigate its role for host defense in vivo. After infection with PR8M, Irf7-deficient mice exhibited a more pronounced body weight loss and increased mortality compared to wild type mice after infection with H1N1 virus. The gene discussed is IRF7; the disease is infection.