Human gestation-associated tissues express functional cytosolic nucleic acid sensing pattern recognition receptors: Viral TLRs and RLRs at the materno-fetal interface

The role of viral infections in adverse pregnancy outcomes has gained interest in recent years. Innate immune pattern recognition receptors (PRRs) and their signalling pathways, that yield a cytokine output in response to pathogenic stimuli, have been postulated to link infection at the maternal–fetal interface and adverse pregnancy outcomes. The objective of this study was to investigate the expression and functional response of nucleic acid ligand responsive Toll‐like receptors (TLR‐3, −7, −8 and −9), and retinoic acid‐inducible gene 1 (RIG‐I)‐like receptors [RIG‐I, melanoma differentiation‐associated protein 5 (MDA5) and Laboratory of Genetics and Physiology 2(LGP2)] in human term gestation‐associated tissues (placenta, choriodecidua and amnion) using an explant model. Immunohistochemistry revealed that these PRRs were expressed by the term placenta, choriodecidua and amnion. A statistically significant increase in interleukin (IL)‐6 and/or IL‐8 production in response to specific agonists for TLR‐3 (Poly(I:C); low and high molecular weight), TLR‐7 (imiquimod), TLR‐8 (ssRNA40) and RIG‐I/MDA5 (Poly(I:C)LyoVec) was observed; there was no response to a TLR‐9 (ODN21798) agonist. A hierarchical clustering approach was used to compare the response of each tissue type to the ligands studied and revealed that the placenta and choriodecidua generate a more similar IL‐8 response, while the choriodecidua and amnion generate a more similar IL‐6 response to nucleic acid ligands. These findings demonstrate that responsiveness via TLR‐3, TLR‐7, TLR‐8 and RIG‐1/MDA5 is a broad feature of human term gestation‐associated tissues with differential responses by tissue that might underpin adverse obstetric outcomes.