Role of STAT1 in Chlamydia-Induced Type-1 Interferon Production in Oviduct Epithelial Cells.

We previously reported that Chlamydia muridarum-infected murine oviduct epithelial cells (OE cells) secrete interferon β (IFN-β) in a mostly TLR3-dependent manner. However, C. muridarum-infected TLR3-deficient OE cells were still able to secrete detectable levels of IFN-β into the supernatants, suggesting that other signaling pathways contribute to Chlamydia-induced IFN-β synthesis in these cells. We investigated the role of STAT1 as a possible contributor in the Chlamydia-induced type-1 IFN production in wild-type (WT) and TLR3-deficient OE cells to ascertain its putative role at early- and late-times during Chlamydia infection. Our data show that C. muridarum infection significantly increased STAT1 gene expression and protein activation in WT OE cells; however, TLR3-deficient OE cells showed diminished STAT1 protein activation and gene expression. There was significantly less IFN-β detected in the supernatants of C. muridarum-infected OE cells derived from mice deficient in STAT1 when compared with WT OE cells, which suggest that STAT1 is required for the optimal synthesis of IFN-β during infection. Real-time quantitative polymerase chain reaction analyses of signaling components of the type-1 IFN signaling pathway demonstrated equal upregulation in the expression of STAT2 and IRF7 genes in the WT and TLR3-deficient OE cells, but no upregulation in these genes in the STAT1-deficient OE cells. Finally, experiments in which INFAR1 was blocked with neutralizing antibody revealed that IFNAR1-mediated signaling was critical to the Chlamydia-induced upregulation in IFN-α gene transcription, but had no role in the Chlamydia-induced upregulation in IFN-β gene transcription.