Abstract
More and more fungal polysaccharides have been reported to exhibit a variety of biological activities, including antitumor, antioxidant and immunostimulant activity. The non-starch polysaccharides have emerged as an important class of bioactive natural products. In this study, the immune activities of a novel polysaccharide (LDG-A) isolated from Lactarius deliciosus (L. ex Fr.) Gray were investigated at 20, 40 and 80 mg/kg dose levels. The inhibitory rate in mice treated with 80 mg/kg LDG-A can reach 68.422%, being the highest in the three doses, which may be comparable to mannatide. Histology of immune organs showed that the tissues were arranged in more regular and firm pattern, but the tumor tissue arranged looser in LDG-A group than those in control group. Meanwhile, there was no obvious damage to other organs, such as heart, lung, and kidney. The antitumor activity of the LDG-A was usually believed to be a consequence of the stimulation of the cell-mediated immune response because it can significantly promote the lymphocyte and macrophage cells in the dose range of 50-200 μg/ml and 100-400 μg/ml in vitro, respectively. The level of cytokines (IL-6, TNF-α, and NO) of macrophage cells induced by LDG-A treatment was similar to lipopolysaccharides at different concentrations. The expression of all these genes studied (TNF-α, IL-6, and iNOS mRNA) in the untreated macrophage was little, but increased dramatically in a dose-dependent manner in the LDG-A-treated cells. The results obtained in the present study indicated that the purified polysaccharide of L. deliciosus (L. ex Fr.) Gray is a potential source of natural immune-stimulating substances.