| Astragalus is used as a Chinese herbal medicine. It contains polysaccharides, proteins, alkaloids, amino acids, flavonoids, glycosides, trace elements and other bioactive substances. APS (Astragalus polysaccharides) is the main bioactive component. APS have various pharmacological effects such as immune activity, cardiac buck, hypoglycemic, anti-stress, anti-tumor, anti-virus, anti-radiation, anti-oxidation and so on. It has been reported that APS has immunoregulatory effects. However, the data on immunomodulating effects of APS are always from either crude or high molecular weight polysaccharides. The present paper describes the purification of LMw-APS which is a homogeneous polysaccharide and investigates the antibody isotypes evoked by LMw-APS.Crude APS ( designated CAPS) isolated with hot water from Astragalus was fractionated by precipitating with ethanol, freezing and thawing to move insoluble materials. Low Molecular Weight (designated LMw-APS) was purified by Sepharose CL-6B gel filtration chromatography after CAPS was deproteinated by the combination of proteinase and Sevage method. HPLC indicated that LMw-APS (Mw=5640) was a homogeneous polysaccharide.Gas chromatography (GC) Analysis showed that LMw-APS was composed of Glc, GalA ,Ara, Rha, Man ,the molar ratio is 51:1.63:1:0.4:0.13.Immunobiological activity mediated by LMw-APS in ICR mice, which were immunized subcutaneously with ovalbumin (OVA) alone or with OVA dissolved in saline containing LMw-APS, was evaluated in this paper. The results showed LMw-APS significantly enhanced the ConA- or LPS-induced splenocyte proliferation; antibody titers (IgG, IgG1, IgG2b ) against OVA in serum from mice immunized with OVA dissolved in LMw-APS were increased significantly when compared with mice injected with OVA alone. The results suggest that LMw-APS enhances immunologic activity of mice. It may be consider as a potential adjuvant to improve the efficacy of vaccine.
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