Background: Recognition of lipopolysaccharide (LPS) is required for effective defense against invading gram-negative bacteria. Recently, in vitro studies revealed that CD14 is required for activation of the myeloid differentiation factor (MyD)88-dependent Toll-like receptor (TLR)4 signaling pathway by smooth (S)-LPS, but not by rough (R)-LPS. The present study investigated the role of CD14 in induction of lung inflammation in mice by these different LPS chemotypes.
Methodology/results: Neutrophil accumulation and tumor necrosis factor (TNF) release in bronchoalveolar lavage fluid were determined 6 hours after intranasal treatment of wild type (WT) and CD14 knock-out (KO) mice with different doses S-LPS or R-LPS. The contribution of CD14 to lung inflammation induced by S-LPS or R-LPS depended on the LPS dose. At low doses, S-LPS and R-LPS induced neutrophil influx in a CD14-dependent manner. Low dose S-LPS-induced cytokine release also depended on CD14. Strikingly, neutrophil influx and TNF release induced by high dose S-LPS or R-LPS was diminished in the presence of CD14. Intranasal administration of sCD14 to CD14 KO mice treated with S-LPS partially reversed the inflammatory response to the response observed in WT mice.
Conclusions: In conclusion, CD14 modulates effects of both S-LPS and R-LPS within the lung in a similar way. Except for R-LPS-induced TNF release, S-LPS and R-LPS at low dose induced acute lung inflammation in a CD14-dependent manner, while the inflammatory response triggered by high dose S-LPS or R-LPS was diminished by CD14.