Dectin-1, the receptor for β-glucans, protects the host against fungal infection; however, its role in intestinal immunity is incompletely understood. We found that Dectin-1-deficient (Clec7a(-/-)) mice were refractory to both dextran sodium sulfate (DSS)- and CD45RB(high)CD4(+) T cell-induced colitis, and that this resistance was associated with an increase in regulatory T (Treg) cells. The proportion of lactobacilli, especially Lactobacillus murinus, in the commensal microflora was increased in Clec7a(-/-) mouse colons, and accompanied by a decrease in antimicrobial peptides induced by Dectin-1 signaling. L. murinus colonization increased Treg cells in the colon. Oral administration of laminarin, a Dectin-1 antagonist, suppressed the development of DSS-colitis, associated with an increase of L. murinus and Treg cells. Human patients with inflammatory bowel disease were found to have a decreased proportion of closely related Lactobacillus species. These observations suggest that Dectin-1 regulates the homeostasis of intestinal immunity by controlling Treg cell differentiation through modification of microbiota.

Reduction in klotho gene expression causes accelerated senescence in klotho mutant mice. We have now found two key substances, phosphorus and zinc, which affect the appearance of klotho phenotypes. Klotho mutant homozygotes fed nonpurified diet with a phosphorus concentration of 1.03 g/100 g showed typical klotho phenotypes. However, most of the klotho phenotypes no longer appeared in male homozygotes fed a 0.4 g/100 g phosphorus diet. These homozygotes were capable of spermatogenesis. In the kidneys of the rescued male homozygotes, klotho protein expression was clearly detected. On the other hand, female klotho mice required supplementation of 0.25 g/100 g zinc orotate to the 0.4 g/100 g phosphorus diet to be rescued. Unlike in the rescued male mice, klotho protein levels in the kidneys of the rescued females were quite low. Wild-type (C3H/He) mice fed 1.5 or 1.0 g/100 g phosphorus diets had lower klotho protein expression in the kidneys than those fed a 0.4 g/100 g phosphorus diet (Kruskal-Wallis test, P < 0.05). These results indicate that dietary phosphorus and zinc modulate the phenotypes of klotho mice, and that klotho expression in the kidneys is regulated not only in klotho mutant mice, but also in wild-type mice.

The cytokines IL-17A and IL-17F have 50% amino-acid identity and bind the same receptor; however, their functional differences have remained obscure. Here we found that Il17f mice resisted chemically induced colitis, but Il17a mice did not, and that Il17f CD45RBCD4 T cells induced milder colitis in lymphocyte-deficient Rag2 mice, accompanied by an increase in intestinal regulatory T cells (T cells). Clostridium cluster XIVa in colonic microbiota capable of inducing T cells was increased in both Il17f mice and mice given transfer Il17f T cells, due to decreased expression of a group of antimicrobial proteins. There was substantial production of IL-17F, but not of IL-17A, not only by naive T cells but also by various colon-resident cells under physiological conditions. Furthermore, antibody to IL-17F suppressed the development of colitis, but antibody to IL-17A did not. These observations suggest that IL-17F is an effective target for the treatment of colitis.