Background: Our previous study showed that an oral administration of Lactobacillus plantarum NRIC0380 inhibited immunoglobulin E (IgE) production in a murine model, and that orally administered NRIC0380 induced CD4+CD25+ Foxp3+ T, i.e. regulatory T (Treg), cells in the spleen and Peyer's patch of mice. Although it has been reported that Treg cells might suppress the allergic symptoms, the involvement of the cells in the antiallergic activity of lactic acid bacteria has not been clearly demonstrated. We therefore examined in detail the antiallergic activity of Treg cells obtained from mice that had been fed NRIC0380. Methods: Treg cells were obtained from mice that had been fed NRIC0380. The T cell-suppressive effect of the cells was analyzed by coculturing the cells with splenocytes of β-lactoglobulin-immunized mice and β-lactoglobulin. The effects of the Treg cells on the IgE production and cutaneous anaphylaxis reaction were then analyzed by transferring the cells into another mouse. Results: The Treg cells obtained from the mice that had been fed NRIC0380 showed similar T cell-suppressive activity to those cells obtained from the control mice. The Treg cells obtained from the mice fed NRIC0380 significantly inhibited the IgE production and active cutaneous anaphylaxis reaction when transferred into another mouse that was subsequently immunized with the antigen. Furthermore, the Treg cells also significantly suppressed the passive cutaneous anaphylaxis reaction when cotransferred with the IgE antibody into another mouse. Conclusions: The induction of Treg cells by the oral administration of NRIC0380 would be involved in the antiallergic activity of NRIC0380.

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Although there have been many studies revealing the mechanism and establishing the therapeutical method for allergic rhinitis, no suitable animal models for allergic rhinitis, especially for pollen allergy, are currently available. We therefore aimed in this study to develop a murine model producing IgE in response to an inhaled antigen without using any adjuvants. Ovalbumin (OVA)-specific T cell receptor transgenic mice (DO11.10) inhaled an OVA solution for one h, twice a week, for six weeks. The resulting increase of OVA-specific IgE in the serum was observed depending on the times of inhalation. Spleen cells from mice that had inhaled the antigen produced more IL-4 and less IFN-γ than those from the control mice in vitro. These results indicate that inhaled antigen enhanced the Th2-type responses and induced IgE production in a T cell-mediated manner. Our findings would contribute to studies on prevention and treatment of pollen allergy.