ISG15 and infection: Accordingly, to examine the possible contributions of IFN and IFN-induced signaling to ISG expression changes at 12 and 48 h postinfection, IIIB infections of CD4+ T cells were carried out in the presence or absence of an antibody specific for the type I IFN receptor (MMHAR-2) that efficiently blocks IFN-induced signaling, and RNA levels of a subset of ISGs (ISG15, IFN-induced protein with tetratricopeptide repeats [IFIT1], and 2′-5′-oligoadenylate synthetase 1 [OAS1]) were then monitored by qPCR.