Purification, characterization and immunomodulatory effects of Plantago depressa polysaccharides

Four purified polysaccharide fractions from seeds of Plantago depressa (PDSP-1, PDSP-2, PDSP-3 and PDSP-4) were obtained by isolation and purification using DEAE-52 cellulose and Sephacryl S-400 HR chromatography. Basic physicochemical properties including molecular weight, chemical composition, FT-IR and glycosidic linkage of these fractions were investigated. They seemed to be homogeneous acidic protein-bound heteropolysaccharides with high molecular weight of over 1000 kDa and contained a lot more β-type glycosidic linkages than α-type. PDSP-3 mainly contained mannose, arabinose and fucose, and the others were rich in arabinose, fucose and galacturonic acid. The immunomodulatory effects of them were assessed by splenocyte proliferation index and production of NO and TNF-α from macrophages. They all showed significant immunomodulatory activities, and PDSP-3 presented the strongest effect. Their observed differences in biological activities were probably due to their structure differences. And monosaccharide compositions, linkage types and molecular weight may affect their immunomodulatory activities.