Background:The present study was undertaken to examine the ability of lipopolysaccharide-containing outer membrane vesicles (OMV-LPS) and purified LPS (P-LPS) from the same meningococcal strain to induce the expression of Toll-like receptors (TLR2 and TLR4) and TNF-alfa production in leukocytes, and further to study the involvement of TLRs, and CD14 in monocyte TNF- alfa production in an ex vivo human whole blood system.Material/Methods:OMV-LPS or P-LPS were added to human whole blood and expression of TLR2/4 and production of TNF- alfa in leukocytes were measured by flow cytometry. To study involvement of TLRs and CD14 in monocyte cytokine production we used monoclonal antibodies against TLR2/4 and CD14.Results:OMV-LPS and P-LPS induced surface expression (maximal at 120 min) of TLR2 and TLR4 on granulocytes and monocytes. LPS incorporated in OMV was less potent (weight basis) than P-LPS in inducing monocyte TNF- alfa production. When inducing monocyte TNF-alfa by OMV-LPS, antibodies directed against TLR2 and TLR4 caused 45 and 78% inhibition, respectively. When inducing TNF- alfa by P-LPS, antibodies against TLR2 had no effect, whereas anti-TLR4 antibodies caused 63% inhibition. Antibodies against CD14 inhibited nearly completely the monocyte TNF- alfa response induced by meningococcal LPS irrespective of whether LPS was presented in purified form or incorporated in membrane vesicles.Conclusions:OMV-LPS and P-LPS from the same meningococcal strain induced expression of TLR2/4 on monocytes and granulocytes. Surface receptors TLR2/4 and CD14 are essential for in vitro cellular activation induced by OMV-LPS and P-LPS, but the functional significance of these receptors during meningococcal infections remains elusive.

Keywords: Antigens, CD14 - metabolism, Lipopolysaccharides - metabolism, Membrane Glycoproteins - metabolism, Monocytes - drug effects, Monocytes - metabolism, Neisseria meningitidis - cytology, Neisseria meningitidis - metabolism, Receptors, Cell Surface - metabolism, Toll-Like Receptor 2, Toll-Like Receptor 4, Toll-Like Receptors, Tumor Necrosis Factor-alpha - metabolism