Polysaccharide fractions extracted from Lactarius quieticolor mushroom exhibit immune stimulatory activities on macrophages

[Display omitted] •Polysaccharides were extracted from Lactarius quieticolor fruiting bodies with cold-, hot-water and alkaline solution•(1→3),(1→6)-β-D-Glucans, (1→6)-α-D-Galactans and (1→4)-β-D-Mannans polysaccharides were observed.•All extracts can elicit immune responses in RAW 264.7 macrophages.•The alkaline extract, having many mannose and 3,6-di-O-substituted units, was the most effective in immune stimulation. Several beneficial properties have already been observed for mushrooms extracts containing polysaccharides, one of the main components present in these fungi. In order to obtain these extracts and clarify their composition, different extraction and characterization methods can be applied, contributing to understanding its biological effects. In this research, we evaluated three different crude fractions obtained through cold water, hot water, and alkaline solution, from the mushroom Lactarius quieticolor. Each sample was totally characterized by NMR (1H, 13C, HSQC-DEPT, COSY), GC–MS (monosaccharide composition and methylation analysis) and HPSEC (homogeneity and relative Mw). The results showed a mixture of different polysaccharides, including D-galactans and D-glucans in each fraction. All the extracts presented immunostimulant activity in murine RAW 264.7 macrophages, stimulating NO secretion and inducing morphological alterations that were typical of activated cells. These effects were more intense for alkaline fraction (EA), which have higher amounts of mannose and 3,6-di-O-substituted-Glcp units. The results obtained show that crude fractions can potentially stimulate immune cells, which indicates that the consumption of this edible mushroom can bring great benefits to health, being considered an excellent food due to its good biological properties.