Interferons induce the expression of hundreds of antiviral genes. Interferons notably stimulate inducible nitric oxide synthase (NOS), thus, the production of large amounts of nitrogen oxyde (NO). A 1993 study by Karupiah et al. (1), that appears to be still factually correct, found that the activity of iNOS is both necessary and sufficient for a substantial antiviral effect of IFN-gamma in vitro.