Meconium-induced release of cytokines is mediated by the TRL4/MD-2 complex in a CD14-dependent manner

Meconium, the first intestinal discharge of the newborn, contains material accumulated during fetal life. Meconium activates complement and CD14 and may induce a systemic inflammatory response. Toll-like receptors are classical pattern-recognition receptors recognizing both exogenous and host-derived ligands. The cyanobacterial product CyP is a potent LPS antagonist binding to the TLR4/MD-2 complex. The aim of the present study was to investigate the role of the CD14/TLR4/MD-2 complex in meconium-induced inflammation.

Whole blood from six donors was preincubated with anti-CD14 or CyP. Meconium was added and the samples were incubated for 4h. Twenty-seven inflammatory mediators were measured in a Bioplex Array Reader. Human embryonic kidney cells transfected with plasmids containing NF-kappaB dependent luciferase reporter, human MD-2, TLR4, TLR2 and/or CD14, were incubated with meconium or LPS for 18 h. Luciferase activity in cytoplasmic extracts was measured using a Luciferase Assay System kit.

Meconium induced formation of a broad panel of inflammatory mediators. CyP and anti-CD14 significantly (p<0.001) inhibited meconium-induced formation of (a) proinflammatory cytokines (TNF-alpha, IL-1beta, IL-6, IFN-gamma) by 60-80% and 72-94%, respectively, (b) anti-inflammatory cytokines (IL-10, IL-1Ra) by 58-59% and 50-65%, respectively, (c) chemokines (IL-8, MCP-1, MIP-1alpha, MIP-1beta, eotaxin, IP-10) by 43-77% and 57-87%, respectively, and (d) growth factors (G-CSF, GM-CSF, basic FGF, PDGFbb) by 53-71% and 40-78%, respectively, with no statistical significant difference between Cyp and anti-CD14. The inflammatory response could only partly be explained by LPS, suggesting that endogenous components of meconium contribute to the inflammatory response. Meconium activated NF-kappaB dose-dependently in cells expressing TLR4/MD-2 together with CD14, while no effect was seen in cells expressing TLR4/MD-2 alone or in TLR2/CD14 transfected cells.

The results indicate that the CD14-dependent meconium-induced inflammatory reaction is mediated through the TLR4/MD2 complex. These data may have implications for future therapeutic strategies for meconium aspiration syndrome.