IFN-b Induction by Brucella Requires MyD88/STING Figure 4. IRF3-dependent expression of IFN-b and TRAIL upon Brucella abortus infection. Raw 264.7 macrophages were treated with non- targeting control siRNA, a specific-targeting IRF3 (si1075) or non-treated control (NT). Total mRNA was obtained after 24 hrs stimulation with B. abortus S2308 (103 bact/cell) or poly I:C (10 mg/ml) as positive control. Next, IFN-b (A) and TRAIL (B) transcript levels were measured by real-time RT- PCR. Error bars represent the mean 6SD of samples assayed in triplicate. A representation of at least three experiments is shown. Statistically significant difference from cells treated with si1075 versus non-treated cells is denoted by an asterisk, from Brucella-infected cells treated with si1075 versus non-treated (NT) cells by two asterisks and from poly I:C stimulated cells treated with si1075 versus non-treated cells by three asterisks (p,0.05). doi:10.1371/journal.pone.0023135.g004 pneumophila replication in macrophages [40]. The susceptibility of IFN-abR KO mice to these infections has been correlated with reduced TNF-a and IFN-c production. In response to Francisella tularensis, type I IFN signaling has also been observed to induce the expression of inflammasome components such as IL-1b and IL-18 [41]. Due to the complex cytokine circuit involving type I IFNs, the mechanisms by which the immunomodulatory effects of these IFNs are regulated are only beginning to be understood [42]. Regarding type I IFNs induced by B. abortus infection, the first demonstration that Brucella induces IFN-a was reported by Huang et al [8] using heat-killed bacteria (HKBa). IFN-a was detected in serum of wild type mice injected with HKBa and the level was markedly reduced in the TLR9 KO mice serum, demonstrating that HKBa induces IFN-a in a TLR9-dependent manner. Additionally, Salcedo et al [43] have shown that Brucella is able to induce IFN-b in dendritic cells. In this study, we have demonstrated that Brucella induces IFN-b in BMDM and splenocytes from wild type and IFN-abR KO mice. Furthermore, we demonstrated that type I IFN signaling is detrimental to host control of B. abortus infection since low numbers of bacterial cfu PLoS ONE | www.plosone.org 6 August 2011 | Volume 6 | Issue 8 | e23135