Structural Characterization of a Novel Polysaccharide from Pulp Tissues of Litchi chinensis and Its Immunomodulatory Activity

A novel polysaccharide (LCP50W) with a molecular weight of 4.72 X 10(4) Da was isolated from the pulp tissues of Litchi chinensis. The chemical structure of LCP50W was characterized using physicochemical and instrumental analyses. The results indicated that the main chain of LCP50W consisted of (1 -> 3)-linked beta-L-rhamnopyranosyl, (1 -> 6)-linked alpha-D-glucopyranosyl, and (1 -> 2,6)-linked alpha-D-glucopyranosyl residues, which branched at O-6. The three branches consisted of (1 -> 2)-linked alpha-L-rhamnopyranosyl, (1 -> 3)-linked alpha-D-galactopyranosyl, and (1 -> 3)-linked alpha-L-mannopyranosyl residues, terminated with (1 ->)-linked alpha-L-arabinopyranosyl residues, respectively. The in vitro immunomodulatory assay revealed that LCP50W promoted the proliferation of mouse splenocytes and enhanced the cytotoxicity of NK cells. LCR50W boosted the secretion of Th1 cytokine IFN-gamma while it inhibited the secretion of Th2 cytokine IL-4; it also enhanced the expression of T-bet while it inhibited the expression of GATA-3. Additionally, LCP50W promoted the development of cell cycle toward the S phase.