TNF and infection: In the case of mild disease from A/Aichi/2/68 or A/Puerto Rico/8/34 infection, ferrets showed strong upregulation of IFN-alpha, IFN-gamma, and TNF-alpha early after infection, while the more pathogenic strains investigated, A/USSR/90/1977 and A/Port Chalmers/1/73, elicited delayed activation of IFN-alpha and IFN-gamma [63].