IFNs are also associated with up-regulation of p21 (a known apoptotic regulator), inducible NO synthase (iNOS), major histocompatibility complex (MHC) proteins, granzyme, and cytotoxic T lymphocyte epitope presentation [122,127,128], all of which are involved in biological processes of anti-viral infection [122,129]. Here, NOS2 is linked to viral infectious disease.