Immunostimulatory activities of yam tuber mucilages

The purified mucilages from three Taiwanese yam cultivars, including Dioscorea alata L. cv. Tainong 1 (TN1), D. alata L. cv. Tainong 2 (TN2), and D. alata L. var. purpurea (Roxb.) cv. Ming-Jen (MJ), and the commercial lentinan (Len) were used to evaluate the immunostimulatory effects on the murine innate and adaptive immunity. BALB/c mice were grouped and administrated orally with 0.5 ml of TN1, TN2, MJ daily for 5 weeks. The positive and negative controls were fed with lentinan and distilled water, respectively. Blood samples were drawn from the retroorbital sinus on day 7 and 21, and the lymphocyte subpopulation, phagocytosis of granulocyte and monocyte were analyzed by flow cytometry. The mice were sacrificed on day 36, and the splenocytes were harvested for determinations of natural killer (NK) cell cytotoxicity activity. The stimulation index on the phagocytosis of peritoneal macrophages and the RAW264.7 cell line by yam mucilage were also determined in vitro. The results showed that all three mucilages, especially MJ yam, could elevate the number of T helper cells in the peripheral blood and enhance the phagocytic activity of granulocyte, monocytes and macrophages both ex vivo and in vitro tests. Increased splenic cytotoxic activity following the administration of mucilages from MJ yam was observed. Furthermore, the production of specific anti-ovalbumin (OVA) antibody and OVA-stimulated splenic cell proliferation were also enhanced by all mucilage groups. It is suggested that the tuber mucilage may function as an immunomodulatory substance.