Regulation of interactions of endotoxin with host cells

• Published in: Journal of endotoxin research 2003-01, Vol.9 (6), p.401-408
• Main Authors: Gioannini, Theresa L., Teghanemt, Athmane, Zarember, Kol A., Weiss, Jerrold P.
• Format: Article
• Language: English
• Subjects: CD14 antigen; lipooligosaccharides; Neisseria meningitidis; TLR4 protein; Toll-like receptors
• ISSN: 0968-0519
• DOI: 10.1179/096805103225002773

`otent Toll-like receptor 4 (TLR4)-dependent cell activation by endotoxin requires lipopolysaccharide-binding protein (LBP) and CD14-dependent delivery of endotoxin to cells containing MD-2 and TLR4. We have used metabolically labeled [ super(14)C] meningococcal lipooligosaccharide (LOS), purified recombinant endotoxin-binding proteins, and cultured endothelial cells to better define protein:endotoxin intermediates key in cell activation in the absence of functional membrane (m) CD14. Protein:endotoxin complexes or aggregates (agg) were purified by gel sieving and characterized by immunocapture and bio-assays. Cell activation closely correlated with LBP, albumin and soluble (s) CD14-dependent conversion of endotoxin agg (M sub(r) greater than or equal to 20 x 10 super(6)) to monomeric (M sub(r) similar to 55 x 10 super(3)) endotoxin:sCD14 complexes. Ordered interaction of LBP (+ albumin) and sCD14 with LOSagg was required for the efficient formation of a bioactive endotoxin:sCD14 complex and potent cell activation. Increasing the ratio of LBP/sCD14 or addition of bactericidal/permeability-increasing protein (BPI) reduced accumulation of endotoxin:sCD14 complexes and instead yielded aggregates of endotoxin (M sub(r) similar to 1-20 x 10 super(6)) containing LBP or BPI that were taken up by cells in a CD14- and TLR4-independent manner without inducing proinflammatory responses. These findings strongly suggest that host machinery linked to TLR4-dependent cellular activation or TLR4-independent cellular clearance of endotoxin selectively recognizes different protein:endotoxin complexes. At the outset of infection, the low concentrations of LBP present and absence of extracellular BPI favor formation of pro-inflammatory endotoxin:CD14 complexes. The mobilization of LBP and BPI that is triggered by inflammation directs endotoxin for clearance and hence resolution of endotoxin-triggered inflammation.