Abstract

BACKGROUND: The pro-inflammatory potential of lipoteichoic acid (LTA) fromStaphylococcus aureus is controversial. The present study was undertaken to examine the ability of highlypurified and characterized S. aureus LTA to stimulate the production of pro-inflammatory cytokines inhuman leukocytes at both mRNA and protein level, and to study the involvement of Toll-like receptors(TLRs) and CD14 in this response. MATERIAL/METHODS: Purified LTA was administered to whole human bloodex-vivo (or primary adherent monocytes) and the cytokine response assessed in plasma by EIA. CytokinemRNA was measured by RT-PCR on leukocyte subsets isolated following stimulation. To study the involvementof 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 humanwhole blood or primary adherent human monocytes elicited a time and concentration dependent release oftumor necrosis factor alpha (TNF-alpha), interleukin-1 beta (IL-1 beta), IL-6 and IL-8. Messenger RNAencoding TNF-alpha, IL-1 beta and IL-6 seemed to be accumulated in monocytes and T cells, but not ingranulocytes and B cells. Expression of TLR2, but not TLR4, in chinese hamster ovary cells conferredresponsiveness to LTA. However, antibodies directed towards TLR2 (clone TL2.1) or TLR4 (clone HTA125)failed to inhibit TNF-a release induced by LTA in both the whole blood model and in adherent monocytes.In contrast, blockade of the CD14 receptor with MAb18D11 strongly attenuated the LTA induced releaseof TNF-alpha in both models. CONCLUSIONS: We propose that (i) LTA from S. aureus triggers the releaseof cytokines during staphylococcal infections, and (ii) both monocytes and T cells contribute to cytokineproduction induced by LTA. TLR2 may mediate cellular activation by LTA, but the functional significanceof this receptor during staphylococcal infections remains elusive.

Keywords: Actins, Antibodies, Monoclonal, Antigens, CD14, CHO Cells, Cell Adhesion, Cells, Cultured, Cytokines, Dose-Response Relationship, Drug, Drosophila Proteins, Hamsters, Kinetics, Membrane Glycoproteins, Monocytes, RNA, Messenger, Receptors, Cell Surface, Reverse Transcriptase Polymerase Chain Reaction, T-Lymphocytes, Teichoic Acids, Time Factors