Tumor Necrosis Factor Alpha Exerts Powerful Anti-Influenza Virus Effects in Lung Epithelial Cells

Previous studies have associated influenza virus-induced expression of inflammatory cytokines, including tumor necrosis factor alpha (TNF-α), with influenza pathogenesis in the human respiratory tract and have suggested that alpha and beta interferons are the first cytokines recruited to counteract such infection. However, we report here that TNF-α has powerful anti-influenza virus activity. When infected with influenza virus, cultured porcine lung epithelial cells expressed TNF-α in a dose-dependent manner. Expression of TNF-α was induced only by replicating virus. TNF-α showed strong antiviral activity against avian, swine, and human influenza viruses, and the antiviral effect of TNF-α was greater than that of gamma or alpha interferon. These findings suggest that TNF-α serves as the first line of defense against influenza virus infection in the natural host.