Cutting edge: Repurification of lipopolysaccharide eliminates signaling through both human and murine toll-like receptor 2

Toll-like receptor (TLR) 2 has recently been associated with cellular respo nses to numerous microbial products, including LPS and bacterial lipoprotei ns. However, many preparations of LPS contain low concentrations of highly bioactive contaminants described previously as "endotoxin protein," suggest ing that these contaminants could be responsible for the TLR2-mediated sign aling observed upon LPS stimulation. To test this hypothesis, commercial pr eparations of LPS were subjected to a modified phenol re-extraction protoco l to eliminate endotoxin protein, While it did not influence the ability to stimulate cells from wild-type mice, repurification eliminated the ability of LPS to activate cells from C3H/HeJ (Lps(d)) mice. Additionally, only ce ll lines transfected with human TLR4, but not human or murine TLR2, acquire d responsiveness to both re-extracted LPS and to a protein-free, synthetic preparation of lipid A, These results suggest that neither human nor murine TLR2 plays a role in LPS signaling in the absence of contaminating endotox in protein.