Immune-enhancing effects of polysaccharides from purple sweet potato.

Abstract

Immune-enhancing effects of three kinds of purple sweet potato polysaccharides (PSPPs) including water-soluble polysaccharide (WSP), dilute alkali-soluble polysaccharide (DASP) and concentrated alkali-soluble polysaccharide (CASP) were evaluated. Scanning electron microscope analysis showed that all PSPPs could stimulate the formation of microvilli-like structures in cellular surfaces, which was possibly related to activation of macrophages. Neutral red uptake assay showed that PSPPs could increase the phagocytic activity of cells. High dose (400\u202fμg/mL) of PSPPs could notably augment the level of nitric oxide (NO). ELISA analysis revealed that 200 and 400\u202fμg/mL of PSPPs distinctly elevated the production of IL-1β. Cells received 200 and 400\u202fμg/mL of WSP as well as 400\u202fμg/mL of DASP exhibited higher level of IL-6. Results of animal experiments showed that WSP treatment (400\u202fmg/kg) could promote the secretions of IgA, IgG, IgM and sIgA in both normal and immunosuppressed mice. Moreover, CASP treatment (400\u202fmg/kg) elevated the production of IgM in the serum of normal and immunosuppressive mice, while DASP (400\u202fmg/kg) only improved the secretion of IgM in normal mice. In summary, all three polysaccharides can stimulate immune responses of macrophages and positively regulate adaptive immunity by enhancing the production of immunoglobulins in mice.