TLR4 is a member of the recently identified Toll-like receptor family of pr
oteins and has been putatively identified as Lps, the gene necessary for po
tent responses to lipopolysaccharide in mammals. In order to determine whet
her TLR4 is involved in lipopolysaccharide-induced activation of the nuclea
r factor-kappa B (NF-kappa B) pathway, HEK 293 cells were transiently trans
fected with human TLR4 cDNA and an NF-kappa B-dependent luciferase reporter
plasmid followed by stimulation with lipopolysaccharide/CD14 complexes. Th
e results demonstrate that lipopolysaccharide stimulates NF-kappa B-mediate
d gene expression in cells transfected with the TLR4 gene in a dose- and ti
me-dependent fashion. Furthermore, E5531, a lipopolysaccharide antagonist,
blocked TLR4-mediated transgene activation in a dose-dependent manner (IC50
similar to 30 nM). These data demonstrate that TLR4 is involved in lipopol
ysaccharide signaling and serves as a cell-surface co-receptor for CD14, le
ading to lipopolysaccharide-mediated NF-kappa B activation and subsequent c
ellular events.