Lipoteichoic acid from Lactobacillus plantarum induces nitric oxide production in the presence of interferon-gamma in murine macrophages

Abstract

Lipoteichoic acid (LTA) is a major immuno-stimulating component of Gram-positive bacteria. LTA from the beneficial bacterium Lactobacillus plantarum induces weak nitric oxide (NO) production in murine macrophages. Currently, it is not clear if LTA from L plantarum is able to stimulate the innate immune response, even in the presence of inflammation. In the present study, we prepared highly pure and structurally intact LTA from L plantarum and investigated its ability to induce NO in the presence of interferon (IFN)-gamma in the RAW 264.7 murine macrophage cell line and bone marrow-derived macrophages (BMMs) from mice. L. plantarum LTA alone was unable to induce NO production, even at 30 mu g/ml. However, LTA in the presence of IFN-gamma significantly induced NO production in RAW 264.7 cells. The observed NO production was inhibited by a NO synthase (NOS) inhibitor L-NAME and an inducible NOS (iNOS) inhibitor L-NIL, suggesting that iNOS is specifically required for this action. Western blot analysis and reverse transcription and polymerase chain reaction further confirmed that L. plantarum LTA increased protein and mRNA levels of iNOS, respectively. However, such induction was substantially inhibited in BMMs from Toll-like receptor 2 (TLR2)-deficient mice and the macrophages treated with an inhibitor blocking platelet-activating factor receptor. In addition, L plantarum LTA plus IFN-gamma induced IFN-beta expression and STAT1 phosphorylation, which are key pathways for inducing iNOS expression. Electrophoretic mobility shift assay demonstrated that L plantarum LTA in the presence of IFN-gamma remarkably increased the DNA-binding activity of NF-kappa B transcription factor, which is known to be involved in the iNOS gene expression. Collectively, these results suggest that LTA from L. plantarum alone has no inflammatory potential but does induce NO production under conditions of inflammation, such as the presence of IFN-gamma. (C) 2011 Elsevier Ltd. All rights reserved.