Immune-stimulating activity of water-soluble extracellular polysaccharide isolated from Rhizobium massiliae

The aim of this study is to investigate biochemical properties of water-soluble extracellular polysaccharide (WSP) from a novel bacterial strain designated to CA-1 and classified to Rhizobium massiliae by 16S rDNA sequence determination and homology analysis. The main composition of WSP was determined to be glucose by HPAEC. We evaluated immunomodulatory effects of WSP on RAW 264.7 macrophage activation. The results showed that the WSP dose-dependently induced the release of the pro-inflammatory cytokines such as TNF-α and IL-6. In addition, WSP induced nitric oxide synthase (iNOS) expression and increased the production of nitric oxide (NO). Intriguingly, WSP remarkably increased the mRNA expression of Toll-like receptor- 2 (TLR-2) and the phosphorylation of MAPKs (ERK, JNK and p38) in RAW 264.7 cells. These results indicated that WSP activates macrophages to secrete pro-inflammatory cytokines and induces iNOS expression via the activation of the TLR-2/MAPKs signaling pathways. Conclusively, we suggest that WSP of R. massiliae CA-1 can be a new immunomodulatory enhancing the early innate immunity.