Allergen-specific oral immunotherapy combined with kakkonto enhances the efficacy of the oral immunotherapy in a murine food allergy model

Oral immunotherapy (OIT) has been considered a promising approach for food allergies (FAs). However, the current OIT strategy is limited in terms of the long-term efficacy and safety. We have previously demonstrated that kakkonto, a traditional Japanese herbal medicine, suppresses the occurrence of allergic symptoms in a murine model of ovalbumin (OVA)-induced FA, which is attributed to the induction of the Foxp3+ CD4+ regulatory T cells. In this study, we established an OIT model using the FA mice with already established allergic symptoms and determined whether kakkonto could improve the efficacy of OIT. The OIT method consisted of initially administrating a very small amount of OVA and slowly increasing the amount. Allergic symptoms decreased in the OIT-treated FA mice. OIT significantly downregulated Th2 immune response-related gene expression in the FA mouse colon, and decreased a level of mouse mast cell protease-1, a marker of mast cell degranulation in the FA mouse plasma. Furthermore, the concomitant use of kakkonto significantly enhanced the effectiveness of OIT on the allergic symptoms, the Th2 immune responses and the mast cell degranulation in the OIT-treated FA mice. In addition, OIT significantly increased the population of Foxp3+ CD4+ regulatory T cells in the FA mouse colon, and this population was further increased by OIT in combination with kakkonto. Furthermore, the combined therapy with kakkonto reduced the expression of RA-degrading enzyme CYP26B1 mRNA in the FA mouse colon. These findings indicated that the combination of OIT with kakkonto represents a promising approach for FA treatment. To elucidate the mechanism underlying therapeutic effects of oral immunotherapy (OIT) and combined therapy of OIT and kakkonto, we established an OIT model using the food allergy mice with already established allergic symptoms. Kakkonto was administrated 1 h before each oral heated OVA challenge for a combination therapy. Total RNA was extracted from the proximal colon.