Abstract An a-d-glucan (RR1) composed of (1Y4) linked back bone and (1Y6) linked branches with a molecular mass of N550 kDa and exhibiting unique immune stimulating properties is isolated and characterized from the medicinal plant Tinospora cordifolia. This novel polysaccharide is noncytotoxic and nonproliferating to normal lymphocytes as well as tumor cell lines at 0-1000 Ag/ml. It activated different subsets of the lymphocytes such as natural killer (NK) cells (331%), T cells (102%), and B cells (39%) at 100 Ag/ml concentration. The significant activation of NK cells is associated with the dose-dependent killing of tumor cells by activated normal lymphocytes in a functional assay. Immune activation by RR1 in normal lymphocytes elicited the synthesis of interleukin (IL)-1h (1080 pg/ml), IL-6 (21,833 pg/ml), IL-12 p70 (50.19 pg/ml), IL-12 p40 (918.23 pg/ml), IL-18 (27.47 pg/ml), IFN-g (90.16 pg/ml), tumor necrosis factor (TNF)-a (2225 pg/ml) and monocyte chemoattractant protein (MCP)-1 (2307 pg/ml) at 100 Ag/ml concentration, while it did not induce the production of IL-2, IL-4, IL-10, interferon (IFN)-a and TNF-h. The cytokine profile clearly demonstrates the Th1 pathway of T helper cell differentiation essential for cell mediated immunity, with a self-regulatory mechanism for the control of its overproduction. RR1 also activated the complements in the alternate pathway, demonstrated by a stepwise increase in C3a des Arg components. Incidentally, RR1 stimulation did not produce any oxidative stress or inducible nitric oxide synthase (iNOS) in the lymphocytes or any significant increase in nitric oxide production. The water solubility, high molecular mass, activation of lymphocytes especially NK cells, complemen
