Potentiation of Innate Immunity by β-Glucans.

β-Glucans have been known to exhibit antitumor activities by potentiating host immunity by an unknown mechanism. The C-type lectin dectin-1, a β-glucan receptor, is found on the macrophage and can recognize various β-glucans. Previously, we demonstrated the presence of β-glucan receptor, dectin-1, on the Raw 264.7 cells as well as on murine mucosal organs, such as the thymus, the lung, and the spleen. In order to investigate immunopotentiation of innate immunity by β-glucan, we stimulated a murine macrophage Raw 264.7 cell line with β-glucans from Pleurotus ostreatus, Saccharomyces cerevisiae, and Laminaria digitata. Then, we analyzed cytokines such as tumor necrosis factor (TNF)-α and interleukin (IL)-6 by reverse transcription-polymerase chain reaction (RT-PCR). In addition we analyzed gene expression patterns in β-glucan-treated Raw 264.7 cells by applying total mRNA to cDNA microarray to investigate the expression of 7,000 known genes. When stimulated with β-glucans, the macrophage cells increased TNF-α expression. When co-stimulation of the cells with β-glucan and lipopolysaccharide (LPS), a synergy effect was observed by increased TNF-α expression. In IL-6 expression, any of the β-glucans tested could not induce IL-6 expression by itself. However, when co-stimulation occurred with β-glucan and LPS, the cells showed strong synergistic effects by increased IL-6 expression. Chip analysis showed that β-glucan of P. ostreatus increased gene expressions of immunomodulating gene families such as kinases, lectin associated genes and TNF-related genes in the macrophage cell line. Induction of TNF receptor expression by FACS analysis was synergized only when co-stimulated with β-glucan and LPS, not with β-glucan alone. From these data, β-glucan increased expressions of immunomodulating genes and showed synergistic effect with LPS.