The Fruiting Bodies, Submerged Culture Biomass, and Acidic Polysaccharide Glucuronoxylomannan of Yellow Brain Mushroom Tremella mesenterica Modulate the Immunity of Peripheral Blood Leukocytes and Splenocytes in Rats with Impaired Glucose Tolerance

The prevalence of diabetes mellitus (DM), a chronic disease with hyperglycemia and impaired immune function, is increasing worldwide. Progression from impaired glucose tolerance (IGT) to type 2 DM has recently become a target for early intervention. The fruiting bodies (FB) and submerged culture mycelium (CM) of Tremella mesenterica, an edible and medicinal mushroom, have been demonstrated to have antihyperglycemic and immunomodulatory activities in type 1 DM rats. Herein, we investigated the effects of acidic polysaccharide glucuronoxylomannan (GX) extracted from CM on the immunocyte responses. Male Wistar rats were injected with streptozotocin (65 mg/kg) plus nicotinamide (200 mg/kg) for the induction of IGT, and gavaged daily with vehicle, FB, CM, or GX (1 g/kg/day). Rats injected with saline and gavaged vehicle were used as controls. Two weeks later, peripheral blood leukocytes (PBLs) and splenocytes were collected. Ingestion of FB, CM, and GX significantly decreased blood glucose levels in the postprandial period and in oral glucose tolerance test, and partially reversed T-splenocytic proliferation in IGT rats. CM significantly decreased T-helper lymphocytes in the PBLs and B-splenocytes. In addition, FB, CM, and GX significantly reversed the IGT-induced decreases in tumor necrosis factor-α production; GX significantly increased interleukin-6 production in T-lymphocytes in the PBLs and splenocytes; and CM and GX significantly reversed IGT-induced decrease in interferon-γ production in T-lymphocytes in the spleen. In conclusion, FB, CM, and acidic polysaccharide GX of T. mesenterica may increase T-cell immunity via the elevation of proinflammatory and T-helper cytokine production in rats with impaired glucose tolerance.