Structural features and immunomodulatory activities of polysaccharides of longan pulp

An aqueous extract of polysaccharides from longan pulp was chromatographed on a DEAE anion-exchange column to yield four fractions (LPI–IV). Immunomodulatory activities of these polysaccharides were also evaluated in vitro. The purified products, neutral polysaccharide LPI, polysaccharide–protein complex LPII and acidic polysaccharides LPIII and LPIV, exhibited conspicuous differences in their monosaccharide composition, molecular mass and glycosidic linkages. Except for LPI, the other three significantly stimulated lymphocyte proliferation in the dose range of 100–400 μg/mL compared with the normal control (P < 0.05), and might electively stimulate B cells, but not T cells. Furthermore, their stimulations on normal/lipopolysaccharide-induced proliferation and depressions on concanavalin A-induced proliferation could be ordered as LPIII > LPIV > LPII > LPI. All the fractions had the optimal dose of 100 μg/mL on enhancing macrophage phagocytosis. Among them, LPII had the considerable yield and activity for exploiting as a potential immunoadjuvant.