dsRNA-Mediated Nitric Oxide Response Figure 2. Nitric oxide is synthesized by iNOS in response to dsRNA in MEFs. (A) Nitric oxide was produced following treatment with poly I:C in MEFs as determined by Griess assay. (B) DETA-NO, a nitric oxide donor, induced nitric oxide production in MEFs. Nitric oxide produced via DETA-NO limited initiation of replication of HSV-1gfp in WT (C) and IRF32/292/2 (D) MEFs, as measured by GFP fluorescence, where fluorescence levels in mock treated cultures were set to 100%. DETA alone did not induce nitric oxide production and failed to reduce initiation of HSV-1 replication. (E) The relative abundance of iNOS mRNA, measured by qRT-PCR, in WT and IRF32/292/2 MEFs treated with poly I:C was found to be significantly higher in MEFs deficient for IRF3 and IRF9 after 5 hours of poly I:C treatment in comparison to WT counterparts. Fold changes in transcript levels were compared relative to the housekeeping gene, Gapdh. *, p,0.05, **, p,0.01, ***, p,0.0001. Data are expressed as the mean 6 SEM; n = 3. doi:10.1371/journal.pone.0031688.g002 PLoS ONE | www.plosone.org 4 February 2012 | Volume 7 | Issue 2 | e31688