Dendrobium tosaense is a medicinal Dendrobium species widely used in traditional medicine. This study demonstrated some structural characterizations and immunomodulatory activity of the water-soluble polysaccharides derived from the stem of D. tosaense (DTP). DTP was fractioned using DEAE-650 M anion-exchange gel filtration chromatography, producing one neutral polysaccharide fraction (DTP-N), which was investigated for its structural characteristics, using HPAEC-PAD, HP-SEC, GC-MS, and NMR spectroscopy. DTP and DTP-N consisted of galactose, glucose, and mannose in ratios of 1:9.1:150.7 and 1:12.2:262.5, respectively. DTP-N comprised (1 → 4)Man as its main backbone, and its average molecular weight was 220 kDa. We also investigated the immunomodulatory effects of DTP administered orally to BALB/c mice for 3 weeks. DTP substantially boosted the population of splenic natural killer (NK) cells, NK cytotoxicity, macrophage phagocytosis, and cytokine induction in splenocytes. This is the first study to demonstrate the structural characteristics of an active polysaccharide derived from D. tosaense and its immunopharmacological effects in vivo.
