Lipopolysaccharide Could Be Internalized into Human Peripheral Blood Mononuclear Cells and Elicit TNF-α Release,but not via the Pathway of Toll-Like Receptor 4 on the Cell Surface

Lipopolysaccharide(LPS),the principal component of the outer membrane of Gram-negative bacteria,stimulatesvarious cell types to release numerous proinflammatory mediators such as TNF-α,IL-6 and IL-12,which maydamage cells and lead to organ injury,even sepsis and septic shock.Toll-like receptor 4(TLR4) has beenidentified as the receptor involved in the recognition of LPS,but the role of LPS uptake in activating signaltransduction remains controversial.In the present study,TNF-α was used as a marker of macrophages/monocytes activated by LPS,and CQ was used as an inhibitor of endosome mature in order to definitude whatstage of the signal transduction elicited by LPS was interrupted.We found that there indeed existedinternalization of LPS and internalization partially participated in LPS signaling since CQ inhibited cytokinerelease,and decreased accumulation of FITC-LPS in hPBMCs.In contrast,anti-hTLR4 antibody coulddecrease cytokine release,but had no inhibition on accumulation of FITC-LPS.This result revealed thatinhibition of cytokine release was related to reduction of FITC-LPS accumulation in the cells.But TLR4 on thecell surface couldn't participate in internalization of LPS.Thus,LPS signaling and internalization couldn't beviewed as mutually independent processes.Cellular & Molecular Immunology.2004;1(5):373-377.