Human Fetal Membranes Generate Distinct Cytokine Profiles in Response to Bacterial Toll-Like Receptor and Nod-Like Receptor Agonists1

TLDR

Bacterial infection triggers inflammation that weakens fetal membranes and can cause preterm premature rupture, with proinflammatory cytokines such as IL‑1β upregulating matrix metalloproteinases and inducing apoptosis, and innate immune pattern‑recognition receptors (TLR and NLR) mediating this response at the maternal–fetal interface. The study aimed to determine the cytokine profiles produced by fetal membranes in response to bacterial TLR and NLR agonists (PDG, LPS, flagellin, CpG ODN, iE‑DAP, MDP). The authors stimulated fetal membranes with each agonist and measured cytokine production, thereby characterizing the distinct inflammatory responses elicited by each TLR and NLR ligand. Fetal membranes produced distinct cytokine profiles for each bacterial TLR and NLR agonist, with IL‑1β and RANTES upregulated by all five PAMPs, CpG ODN inducing only mild MCP‑1 stimulation and downregulating basal cytokines, IL‑1β secretion linked to processing and caspase‑1 dependence for TLR2/4/5 but caspase‑1‑independent for Nod1/2, demonstrating PRR‑specific inflammatory mechanisms.

Abstract

Bacterial infection-associated inflammation is thought to be a major cause of preterm premature rupture of membranes. Proinflammatory cytokines, such as interleukin 1B (IL1B), can weaken fetal membranes (FM) by upregulating matrix metalloproteinases and inducing apoptosis. The mechanism by which infection leads to inflammation at the maternal–fetal interface and subsequent preterm birth is thought to involve innate immune pattern recognition receptors (PRR), such as the Toll-like receptors (TLR) and Nod-like receptors (NLR), which recognize pathogen-associated molecular patterns (PAMPs). The objective of this study was to determine the cytokine profile generated by FMs in response to the bacterial TLR and NLR agonists peptidoglycan (PDG; TLR2), lipopolysaccharide (LPS; TLR4), flagellin (TLR5), CpG ODN (TLR9), iE-DAP (Nod1), and MDP (Nod2). PDG, LPS, flagellin, iE-DAP, and MDP triggered FMs to generate an inflammatory response, but the cytokine profiles were distinct for each TLR and NLR agonist, and only IL1B and RANTES were commonly upregulated in response to all five PAMPs. CpG ODN, in contrast, had a mild stimulatory effect only on MCP-1 and primarily downregulated basal FM cytokine production. IL1B secretion induced by PDG, LPS, flagellin, iE-DAP, and MDP was associated with its processing. Furthermore, FM IL1B secretion in response to TLR2, TLR4, and TLR5 activation was caspase 1-dependent, whereas Nod1 and Nod2 induced IL1B secretion independent of caspase 1. These findings demonstrate that FMs respond to different bacterial TLR and NLR PAMPs by generating distinct inflammatory cytokine profiles through distinct mechanisms that are specific to the innate immune PRR activated.