The isoflavone puerarin induces Foxp3+ regulatory T cells by augmenting retinoic acid production, thereby inducing mucosal immune tolerance in a murine food allergy model.

Abstract

The disruption of intestinal mucosal immune tolerance can lead to the development of intestinal immune diseases such as food allergy (FA). Regulatory T cells (Tregs) in the mucosa play a critical role in maintaining peripheral immune tolerance in the intestine, and retinoic acid (RA) is absolutely required for the induction of Tregs. We have previously reported that kakkonto, a traditional Japanese herbal medicine, suppresses FA in a murine FA model due to the induction of Tregs in the colonic mucosa. However, the precise molecular mechanisms underlying the induction of Tregs remain unclear. Puerarin, an isoflavone derivative, is a major constituent of kakkonto. Thus, we investigated the effect of puerarin on the induction of Tregs. BALB/c mice were systemically sensitized and then orally challenged with ovalbumin (OVA) as an FA model. Puerarin treatment suppressed the development of allergic diarrhea in FA mice. The gene expression levels of IL-4 and mast cell protease I (mMCP-1) were significantly upregulated in the proximal colon of FA mice but were reduced by puerarin. The proportions of Foxp3+CD4+ cells and CD103+CD11c+ dendritic cells (DCs) were significantly higher among the colonic lamina propria (cLP) cells of puerarin-treated FA mice than among those of untreated FA mice. The gene expression of Aldh1a1, an RA synthesis enzyme, in colonic epithelial cells (CECs) was significantly higher in the puerarin-treated FA mouse colon than in the untreated FA mouse colon. In addition, the preventive effect of puerarin was suppressed in the FA model by pretreatment with LE540, an RA receptor (RAR) antagonist. The induction of Foxp3+CD4+ cells and CD103+CD11c+ DCs by puerarin was reduced by pretreatment with LE540. The present findings indicate that the augmentation of RA production in CECs induced by puerarin enhances the induction of Tregs and suppresses the development of FA in a mouse model. Thus, a natural enhancer of RA production, such as puerarin, has the potential to treat immune diseases attributed to Treg deficiency.