Immunomodulating activities in bran extracts of Japanese red, black and brown rices.

To determine the potent immunomodulating activities of different types of Japanese rice bran, we analyzed the effects of extracts of red, brown and black rice brans on the cell proliferation and cytokine production of mouse immunocompetent cells by cell culture experiments. Methanol extracts of these rice brans showed suppressive activities against the proliferative response (3H-thymidine incorporation) of mouse spleen cells induced by concanavalin A (Con A) or lipopolysaccharide (LPS) in the cell culture experiments. Although the black and brown rice bran extracts showed suppressive effects on the production of interferon gamma (IFN gamma) or interleukin 6 (IL-6) in mouse spleen cells induced by Con A or LPS, the red rice bran extract exhibited stimulatory effects on the same cytokine-producing systems. Furthermore, when the effects of these extracts on the production of macropahage-derived inflammatory cytokines such as interleukin-1alpha (IL-1alpha) and tumor necrosis factor alpha (TNF-alpha) were assayed, the red rice bran extract caused a stimulatory effect on the IL-1alpha production from mouse macrophages induced by LPS, but did not show a significant effect on TNF-alpha production. However, the brown and black rice bran extracts exhibited significant inhibitory effects on the production of IL-1alpha and TNF-alpha in the same macrophage culture experiment. A possible mechanism of the immunomodulating activities of the rice bran extracts and the immunopharmacological significance of these findings are discussed.