Characterizations and immunostimulatory activities of a polysaccharide from Arnebia euchroma (Royle) Johnst. roots.

A polysaccharide from Arnebia euchroma (Royle) Johnst. named ARP, was obtained and purified by the hot water extraction, ethanol precipitation and deproteinization of TCA. The molecular weight of the polysaccharide fraction of ARP was calculated to be 1.23 × 10⁴ Da from a calibration curve obtained with dextran standards. Monosaccharide composition analysis revealed that ARP was composed of Gal, Ara, Glu, Man, Rha and Fuc at a molar ratio of 53.8:21.3:11.7:6.8:4.3:2.2. Methylation analysis suggested that ARP was likely an arabinogalactan and that its backbone mainly consisted of Galp residues of 1,6‑linkages and Ara residues of 1,5‑ or 1,3‑linkages. The in vitro experiment indicated that ARP enhanced B- and T-lymphocyte proliferation. A dose-dependent relationship was observed, and a dose of 200 μg/mL resulted in the highest cell viability. In addition, ARP significantly stimulated the production of the cytokine, interferon-γ (IFN-γ), and enhanced B- and T-lymphocyte proliferation. Meanwhile, ARP had little effect on interleukin-2 (IL-2) production. The experiments of the effect of ARP on the activation of macrophage in vitro indicated that ARP significantly enhanced the production of TNF-α, IL-6 and IL-1β which suggested the polysaccharide induced the functional activation of macrophage.