ISG15 and influenza: The present study found that on PID 3, ISGs particularly showed the increase of the expression to a relatively high level in response to H1N1 virus infection in pigs, and many showed even higher level, e.g. OASL, OAS2, MX1, IRF7, IRF3, IFIT1, IFIT2, IFIT3, ISG15, ISG20 and ISG44. Several recent microarray results have also highlighted the common involvement of IFN-mediated anti-viral responses in the acute phase of influenza infections in other animal models, and illustrated the role of interferons in the first line of defense against virus infections [31].