Different contributions of side-chains in beta-D-(1-->3,6)-galactans on intestinal Peyer's patch-immunomodulation by polysaccharides from Astragalus mongholics Bunge

Abstract

Thirteen polysaccharides isolated from an extract of the aerial portions of Astragalus mongholics Bunge demonstrated immunomodulating activity against Peyer's patch immunocompetent cells. Nine of the active polysaccharide fractions were composed of either arabinogalactans, pectic arabinogalactans or pectins. The activities of the arabinogalactans and pectic arabinogalactans were associated with beta-D-(1-->3)-galactan moieties branched with beta-D-(1-->6)-galactooligosaccharide side-chains having degrees of polymerization of 8 or less. Degradation of the beta-D-(1-->3)-galactan or beta-D-(1-->6)-galactosyl side-chains in the arabinogalactans significantly decreased immunomodulating activity. Rhamnogalacturonan I (RG-I) with beta-D-(1-->3,6)-galactosyl side-chains having terminal beta-D-GlcA showed activity in the pectin-enriched fractions. Interestingly, the terminal GlcA was not required for activity of the arabinogalactan-enriched fractions, suggesting at least two different immunomodulating structures.