Induction of cytokine production in human T cells and monocytes by highly purified lipoteichoic acid: involvement of Toll-like receptors and CD14

Background: Pro-inflammatory potential of lipoteichoic acid (LTA) from Staphylococcus aureus is controversial. Present study was undertaken to examine ability of highly purified and characterized S. aureus LTA to stimulate production of pro-inflammatory cytokines in human leukocytes at both mRNA and protein level, and to study involvement of Toll-like receptors (TLRs) and CD14 in this response. Material/Methods: Purified LTA was administered to whole human blood ex-vivo (or primary adherent monocytes) and cytokine response assessed in plasma by EIA. Cytokine mRNA was measured by RT-PCR on leukocyte subsets isolated following stimulation. To study involvement of specific receptors for LTA signaling, CHO cells transfected with CD14 and/or TLR2, TLR4 were used, as well as antibodies directed against these receptors. Results: Addition of highly purified LTA to a whole blood or primary adherent monocytes elicited a time and concentration dependent release of TNF-alpha, IL-1 beta, IL-6 and IL-8. mRNA encoding TNF-alpha, IL-1 beta and IL-6 seemed to be accumulated in monocytes and T cells, but not in granulocytes and B cells. Expression of TLR2, but not TLR4, in chinese hamster ovary cells conferred responsiveness to LTA. However, antibodies directed towards TLR2 (clone TL2.1) or TLR4 (clone HTA125) failed to inhibit TNF-alpha release induced by LTA in the whole blood model and in adherent monocytes. In contrast, blockade of the CD14 receptor with MAb18D11 strongly attenuated LTA induced release of TNF-alpha in both models. Conclusions: (i) LTA from S. aureus triggers release of cytokines during staphylococcal infections, (ii) monocytes and T cells contribute to cytokine production induced by LTA. TLR2 may mediate cellular activation by LTA, but functional significance of this receptor during staphylococcal infections remains elusive.