Activation of innate immunity by neutral polysaccharides from broccoli buds

Edible substances that stimulate the innate immune system are good candidates for functional foods to improve human health. We have previously reported that acidic polysaccharides from broccoli extract exhibit immunostimulatory effects, but neutral polysaccharides have been overlooked. In the present study, we found that neutral polysaccharides have significantly stronger (higher specific activity) immunostimulatory activity than acidic polysaccharides. The hot water extract of broccoli showed the immunostimulatory activity in the silkworm muscle contraction assay, suggesting that it stimulates innate immunity via paralytic peptide pathway. The activity was concentrated in the buds, but not in the stems and stalk. The active substance was recovered in the flow-through fraction of diethylaminoethyl-cellulose column chromatography with neutral polysaccharides. The specific activity of the fraction was significantly higher than that of the acidic polysaccharides from broccoli reported previously. These results suggest that the neutral polysaccharide present in broccoli buds stimulates innate immunity and can be semi-purified by one-step chromatography.