A novel polysaccharide isolated from Litchi chinensis by using a simulated gastric medium and its immunomodulatory...

A novel polysaccharide (LCPA50-S1) with immunomodulatory activity was extracted with simulated gastric medium from Litchi chinensis, and purified by DEAE-52 cellulose column, Sephadex G-50 column and Sephacryl S-300 HR chromatography. The structural characteristics of LCPA50-S1 were expounded through complete acid hydrolysis, partial acid hydrolysis, methylation and instrumental analysis. The results demonstrated that LCPA50-S1 is a heteropolysaccharide with a molecular weight of 1.58 × 10(5) Da. The backbone was composed of (1→4)-linked β-D-glucopyranosyl residues, (1→6)-linked β-D-galactopyranosyl, (1→3,6)-linked β-D-galactopyranosyl residues, (1→4,6)-linked α-D-glucopyranosyl residues and branched at O-6. The branches were consisted of (1→2)-linked α-L-rhamnopyranosyl residues, (1→4)-linked β-D-glucopyranosyl residues, and (1→6)-linked β-D-galactopyranosyl, terminated with (1→)-linked α-L-arabinopyranosyl residues and (1→)-linked β-D-galactopyranosyl residues, respectively. The immunoregulatory activity of LCPA50-S1 was evaluated through determination the effect of LCPA50-S1 on nitric oxide (NO) production of RAW264.7 macrophages and spleen lymphocyte proliferation as well as its cytokines secretion level. The results demonstrated that LCPA50-S1 increased NO and TNF-α production in RAW264.7 macrophages significantly, enhanced the proliferation as well as the interleukin-2 (IL-2) production of splenocytes. The data indicated that LCPA50-S1 had the potential to be explored as a novel natural immunomodulator for application in functional foods and medicine.