ISG15 and infection: The outcomes of the study indicate that the infection of IEC-6 cells with H9N2 avian influenza virus subtypes precipitated an upregulation of pro-inflammatory cytokines, specifically tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6), along with elevated expression levels of type I interferon, IFN-β, and the interferon-stimulated gene, ISG15.