The equine TLR4/MD-2 complex mediates recognition of lipopolysaccharide from Rhodobacter sphaeroides as an agonist.
Lipopolysaccharide (LPS) antagonists inhibit the response of inflammatory cells to LPS, presumably by competitive inhibition, and may be of therapeutic value in the treatment of endotoxemia and sepsis. The inhibitory effects of some LPS antagonists are restricted to certain host species, however, as the same molecules can have significant endotoxic activity in other species. This species-specific recognition appears to be mediated by Toll-like receptor 4 (TLR4) and/or MD-2. We have shown previously that LPS from Rhodobacter sphaeroides ( RsLPS) is an LPS antagonist in human cells but an agonist (or LPS mimetic) in equine cells. In the present study, HEK293 cells were transfected with combinations of human and equine CD14, TLR4 and MD-2, and incubated with either RsLPS or with LPS from Escherichia coli as an endotoxin control. NF-kappaB activation was measured in a dual luciferase assay as an indicator of cellular activation. Our results indicate that E. colic LPS activated NF-kappaB in cells transfected with all combinations of the three receptor proteins, whereas RsLPS activated NF-kappaB only in cells expressing the single combination of equine TLR4 and equine MD-2. We conclude that the TLR4/MD-2 complex is responsible for recognition of RsLPS as an agonist in equine cells.
Lohmann
Katharina L
KL
Department of Large Animal Medicine, University of Georgia, Athens, Georgia, USA. k.lohmann@usask.ca
Vandenplas
Michel L
ML
Barton
Michelle H
MH
Bryant
Clare E
CE
Moore
James N
JN
D000818:Animals; D002460:Cell Line; D006736:Horses; D006801:Humans; D018950:Lipopolysaccharide Receptors / Q000235:genetics; D008070:Lipopolysaccharides / Q000302:isolation & purification / Q000494:pharmacology*; D008869:Microtubule-Associated Proteins / Q000235:genetics*; D016328:NF-kappa B / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012242:Rhodobacter sphaeroides; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000502:physiology*; D014157:Transcription Factors / Q000235:genetics*; D014162:Transfection
D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; C121118:MID2 protein, human; D008869:Microtubule-Associated Proteins; D016328:NF-kappa B; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; D014157:Transcription Factors