OAS1 and infection: Interestingly, MDA-5 (for melanoma differentiation-associated gene 5), MX1 (for myxovirus resistance 1), OAS1 (for oligoadenylate synthetase 1), ISG20 (for Interferon Stimulated Exonuclease Gene 20) and RIG-1 (for reticnoic acide-inducible gene 1) were up-regulated at day 5 after infection (Figure 4C).