Purpose: Pulverized konjac glucomannan (PKGM) is a natural biologically active compound extracted from konjac, a Japanese traditional food. In the present study, we investigated the role of PKGM in intestinal immunity in a mouse model of oxazolone (OXA)-induced colitis.
Methods: C57BL/6(B6) mice were fed PKGM or control food from 2 weeks before the induction of OXA colitis. Body weight change, colon length, and histological change in the colon were examined. The mononuclear cells were purified from colon and stimulated with PMA/ionomycin. The levels of TNF-α, interferon (IFN)-γ, interleukin (IL)-4, and IL-13 from the supernatant were measured by ELISA.
Results: Oral administration of PKGM prevented the body weight loss and shortening of colon length associated with OXA-induced colitis. Histological analysis revealed that the colonic inflammation was improved by the administration of PKGM. The levels of IL-4 and IL-13, the critical inflammatory cytokines in OXA colitis, derived from mononuclear cells from the lamina propria of the colon were significantly suppressed by PKGM administration. PKGM-fed mice showed a significantly lower IL-4/IFN-γ ratio in the colonic lamina propria compared with that in control-fed mice. Fluorescence-activated cell sorting analysis revealed that natural killer (NK) 1.1(+) T cells in the liver were significantly decreased in PKGM-fed mice. Finally, the preventive role of PKGM in OXA-induced colitis was not observed in invariant natural killer T cell-deficient mice.
Conclusions: PKGM ameliorated OXA-induced colitis in mice. This effect is associated with a decreased population of NK1.1(+) T cells and induction of Th1-polarized immune responses.