Induction of regulatory T Cells as a novel mechanism underlying the therapeutic action of Kakkonto, a traditional Japanese herbal medicine, in a murine food allergy model

Background: The number of patients with food allergy (FA) has dramatically increased. Although satisfactory drug therapies for FA are not available, we have found that kakkonto, a traditional Japanese herbal medicine, suppressed the occurrence of allergic symptoms in an FA mouse model. Thus, we investigated whether kakkonto could regulate the activation and differentiation of T cells in the colon. Methods: BALB/c mice were systemically sensitized and then orally challenged with ovalbumin. FA mice were orally treated with kakkonto. Lamina propria (LP) cells from their colons were isolated and analyzed. Results: Kakkonto significantly reduced the proportion of CD69⁺ cells and the elevated helper T cell type 2-specific transcription factor GATA-3 mRNA expression in the LP CD4⁺ T cells, showing that kakkonto has a suppressive effect on the activation and Th2 differentiation of LP effector CD4⁺ T cells of the FA mouse colon. Furthermore, kakkonto significantly increased the proportion of Foxp3⁺CD4⁺ regulatory T cells in the LP CD4⁺ T cells of the FA mouse colon. Similarly, the number of Foxp3-positive cells was dramatically increased in the colonic mucosa of kakkonto-administered FA mice. However, the pharmacological effect and Foxp3⁺CD4⁺ regulatory T cell-inducing ability of kakkonto were not attenuated by the administration of an anti-CD25 monoclonal antibody in the FA model. Conclusions: The induction of Foxp3⁺CD4⁺CD25^- regulatory T cells in the colon as a novel mechanism underlying the therapeutic action of kakkonto could be utilized for the development of a novel anti-FA drug.