IL-10 modulates placental responses to TLR ligands

Problem: Intra-uterine infections increase production of pro-inflammatory cytokines. It is unclear whether different infectious agents determine the relative expression of pro-and anti-inflammatory cytokines. Methods of study: We compared the placental inflammatory response induced by bacterial lipopolysaccharide (LPS, endotoxin from Gram-negative bacteria) with those induced by lipoteichoic acid (LTA, a cell wall component of Gram-positive bacteria). Placental explants from term delivery were treated with either LPS or LTA, in the presence or absence of IL-10, for 24 hrs. Cytokines, prostaglandin E₂ (PGE₂) production and cyclo-oxygenase-2 (COX-2) expression were quantified. Results: Both LTA and LPS significantly induced several cytokines with LPS eliciting more potent effects. IL-6 and IL-8 were induced to comparable levels in response to both LTA and LPS whereas monocyte chemotactic protein-1 (MCP-1) production was induced more by LTA, demonstrating a differential placental response to a specific toll-like receptor (TLR) ligand. IL-10 treatment significantly reduced most pro-inflammatory cytokines as well as PGE₂ induced by both LPS and LTA. Interestingly, IL-10 down-regulated LTA-mediated MCP1 induction, but not that mediated by LPS. Moreover, IL-10 was more effective in down-regulating PGE₂ after LPS- when compared with LTA stimulation. Conclusions: Our results demonstrate that placental exposure to LTA and LPS appear to trigger distinct cytokine responses that can be modulated by IL-10.