Immunostimulatory activity of soybean hull polysaccharide on macrophages

Water-soluble polysaccharide isolated from soybean hull and fractionated using ion-exchange chromatography were investigated to determine their molecular characteristics and immunostimulating activity. In the present study, soybean hull polysaccharide (SHP) was separated and purified to obtain three main fractions (F1, F2 and F3), and their chemical and monosaccharide compositions were analyzed. SHP was mainly composed of carbohydrates (64.3%), proteins (16.2%) and sulfates (12.5%), with minor levels of uronic acid (3.2%), and predominantly contained glucose and mannose as monosaccharides. Moreover, when compared with cells treated with RPMI medium, SHP was revealed to promote the proliferation and pinocytosis of RAW264.7 cells, and to enhance the production of nitric oxide (NO), tumor necrosis factor (TNF)-α, interleukin (IL)-1β and IL-6. Furthermore, flow cytometry demonstrated that CD11b and CD40 were involved in the immune regulation of RAW264.7 cells by SHP. Moreover, western blotting and other experiments revealed that SHP, a type of pathogen-associated molecular pattern, was specifically recognized by the Toll-like receptor 2, which, in turn, upregulated the expression levels of proteins downstream of the mitogen-activated protein kinase and nuclear factor κB pathways. Notably, the immune activity of the F2 fraction was markedly higher than that of the crude polysaccharides. In summary, the purified F2 fraction of SHP may be an effective nutritional supplement for human disorders associated with low immunity.