Endotoxin tolerance induction in human periodontal ligament fibroblasts stimulated with different bacterial lipopolysaccharides.

•Previous stimuli human periodontal ligament fibroblasts (hPDLFs) with low levels of lipopolysaccharide (LPS) induce a state of tolerance.•Ec LPS is better at initiating the responsiveness of hPDLFs than Pg LPS.•Negative regulation of Toll-like receptors (TLRs) may be involved in mediating tolerance in hPDLFs.•Very low doses of LPS pretreatment induce even a robust response to LPS challenge.