Regulation of toll-like receptor 2 and 4 gene expression in murine alveolar macrophages

The authors investigated the regulation of toll-like receptor (TLR) TLR2 and TLR4 gene expression in alveolar macrophage (AM) in response to lipopolysaccharide (LPS) or proinflammatory cytokines in vitro. Treatment of a murine AM cell line, MH-S, with LPS, tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta significantly increased TLR2 mRNA expression, whereas TLR4 mRNA expression remained constant. LPS-mediated TLR2 mRNA up-regulation was attenuated by inhibition of p38 kinase (with SB203580) or nuclear factor (NF)-kappaB (with sulfasalazine or SN-50), but not by inhibition of extracellular signal-regulated kinase (with PD98059) or c-Jun N-terminal kinase (with SP600125), suggesting that LPS may induce TLR2 mRNA expression through p38 kinase and NF-kappaB activation. These results indicate that TLR2 expression up-regulated in AM in response to bacterial respiratory infections may render AM responsive to TLR2 ligands, which may accelerate the innate immunity against pathogens in the lung.