Immunomodulatory Effects of Extracellular beta-Glucan Isolated from the King Oyster Mushroom Pleurotus eryngii (Agaricomycetes) and Its Sulfated Form on Signaling Molecules Involved in Innate Immunity

Abstract

The aim of this study was to determine, using murine RAW 264.7 macrophages, the immunomodulatory effect of extracellular beta-glucan isolated from Pleurotus eryngii (PEBG) and its sulfated derivative (PEBG-S) on signaling molecules implicated in host innate immunity. beta-Glucan was extracted and purified from the mycelial culture using optimal medium concentrations. It was then chemically converted to its sulfated form. Monosaccharide composition of beta-glucan was characterized with p-aminobenzoic acid ethyl ester-derivatized sugars through highperformance liquid chromatography analysis. Fourier transform infrared structural analysis showed an S= O bond at 1250 cm-1 and C-S-O binding at 815 cm-1 in PEBG-S. 13C nuclear magnetic resonance analysis showed 1,3-linked a-D-mannopyranosyl and 1,3-beta-D-glucopyranosyl in PEBG-S. A concentration-dependent increase of nitric oxide production was noticed in RAW 264.7 cells treated with PEBG-S or PEBG; those treated with PEBG-S showed less cytotoxicity than those treated with PEBG. Cellular levels of tumor necrosis factor-a, interleukin-1 beta, and interleukin-6 were increased by PEBG and PEBG-S treatment, suggesting that they have immunomodulatory activity. Real-time polymerase chain reaction array revealed that the expression levels of nuclear factor-.B and Toll-like receptor signaling genes in cells were upregulated by PEBG and PEBG-S. Moreover, the expression of the beta-glucan receptor dectin-2 was significantly upregulated by PEBG and PEBG-S treatment, reflecting immune activation through the dectin-2-Syk-(CARD9/Bcl-10/MALT1) pathway. Our results suggest that PEBG-S could be used as an effective adjuvant or immune enhancer that can be sustainably produced by recycling the by-product of mycelial culture.