Characterization and mesenteric lymph node cells-mediated immunomodulatory activity of litchi pulp polysaccharide fractions

• LP1–3 with different chemical and chain structures were isolated from litchi pulp.
• LP1–3 stimulated mesenteric lymph node cell proliferation and cytokine secretion.
• LP1 showed the best immunomodulatory activity due to its unique structure.

Three water-soluble hetero-polysaccharides, designated LP1–3, were isolated from litchi pulp. Their structures, solution properties and immunomodulatory activities were evaluated. LP1 contained (1 → 4,6)-β-d-Glc and (1 → 4)-α-l-Gal, while LP2 contained (1 → 3)-α-l-Ara and (l → 2)-β-d-Gal, and LP3 contained α-l-Ara and (l → 4)-β-Rha. Their molecular weights ranged from 105,880 to 986,470 g/mol. LP1 had a spherical conformation with hyper-branched structure and LP2 was semi-flexible chain, while the polysaccharide chains of LP3 were cross linked to form network-like conformation in solution. In addition, all fractions strongly stimulated mesenteric lymph node cell proliferation, IFN-γ and IL-6 secretion in the dose range of 25–100 μg/mL compared with untreated control group (p < 0.05). LP1 exhibited the strongest stimulation of mesenteric lymph node cell proliferation and cytokine secretion, which may be attributed to its unique chemical structure and chain conformation. This is the first report on the solution properties and intestinal immunity activities of polysaccharides from litchi pulp.