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

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 β-d-(1 → 3)-galactan moieties branched with β-d-(1 → 6)-galactooligosaccharide side-chains having degrees of polymerization of 8 or less. Degradation of the β-d-(1 → 3)-galactan or β-d-(1 → 6)-galactosyl side-chains in the arabinogalactans significantly decreased immunomodulating activity. Rhamnogalacturonan I (RG-I) with β-d-(1 → 3,6)-galactosyl side-chains having terminal β-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.