Viral infection dampens human fetal membrane type I interferon responses triggered by bacterial LPS

Abstract

The maternal-fetal interface possesses innate immune strategies to protect against infections. We previously reported that prior viral infection of human fetal membranes (FMs) in vitro and mouse FMs in vivo sensitized the tissue to low dose bacterial LPS leading to augmented inflammation. The objective of this study was to examine FM production of type I interferons (IFNs) and IFN-stimulated genes (ISGs) in the context of this polymicrobial model. Human FM explants and pregnant C57BL/6 mice were treated with or without low dose LPS following exposure to media or the γ-herpes virus, MHV-68. FM RNA was analyzed by qRT-PCR for type I IFNs, ISGs, upstream signaling, and MHV-68 open reading frames (ORFs). Pre-exposure to MHV-68 followed by LPS treatment inhibited the ability of LPS to induce human FM type I IFNs (IFNA, IFNB); ISGs (OAS, MxA, APOBEC3G) and upstream signaling mediators (RIG-I, TBK-1). Signaling mediators IRF-3 and IRF-7 were also reduced. In mouse FMs, pre-exposure to MHV-68 followed by LPS treatment reduced the ability of LPS to upregulate Ifna, Ifnb, Mxa, Irf7, and also reduced Irf3. MHV-68 infection of FMs induced ORF45 which targets IRF-7, and this was further augmented in response to a combination of MHV-68 and LPS. Together, these findings indicate that a viral infection blunts FM type I IFN production and signaling in response to LPS leading to a suppressed ISG response. Our studies suggest that a viral infection inhibits this protective FM response by negatively regulating IRF-7 through ORF45, leaving the maternal-fetal interface vulnerable to further viral attack.