OAS1 and viral infectious disease: A single differentially methylated CpG site within OAS2 (2′-5′-oligoadenylate synthetase 2) coupled with altered co-expression was also observed for OAS1 (2′-5′-oligoadenylate synthetase 1), OAS2, and OAS3 (2′-5′-oligoadenylate synthetase 3) [104], which belong to a family of proteins—induced by interferons—that synthesizes 2′,5′-oligoadenylates and are involved in the innate immune response to viral infection [105].