mRNA transcript levels of IFN-b, IL-1b, IL-6, IL-8, CCR5, IP-10, TNF-a, FasL, TRAIL, Mx, 2959-OAS, retinoic acid-inducible gene I (RIG-1), melanoma differentiation-associated antigen 5 (MDA-5), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) genes were analyzed by a two-step real-time RT-PCR assay as described previously [25] . 1 mg of total RNA, prepared from the cells using the RNeasy kit (Qiagen), was reverse transcribed with the QuantiTect reverse transcription kit (Qiagen) following the manufacturer's instructions. The sequences of primers used in the study are listed in Table 1 . The RT reaction was carried out with the RNA after treatment with DNase I at 42uC for 2 min. Real-time PCR was conducted with 1 ml of cDNA in a total volume of 25 ml with the iQ SYBR Green Supermix (Bio-Rad) following the manufacturer's instructions. Relative expression values were normalized using an internal GAPDH control. The fold change of relative gene expression levels was calculated following the formula: 2 (DCt of gene2DCt of GAPDH) [25, 26] . For each reaction, melting curves were analyzed to determine the specificity of each amplicon. To determine the viral RNA level, the total RNA from infected cells was reverse transcribed and cDNA used for Taqman-based real-time PCR (Applied Biosystems) to measure viral M gene transcripts in the infected cells [27] .