Airway exposure initiates peanut allergy by involving the IL-1 pathway and T follicular helper cells in mice

Background: Little is currently known regarding the immunologic mechanism(s) that initiate peanut allergy. Notably, peanut proteins have been detected in house dust, and their levels correlate with peanut allergy prevalence. Objective: This study aimed to develop a new mouse model for peanut allergy and to investigate the immunologic mechanisms involved in peanut allergen sensitization. Methods: To mimic environmental exposure, naive mice were exposed to peanut flour by inhalation for up to 4 weeks. We then analyzed serum levels of IgE antibody and challenged mice with peanut proteins. Immunological mechanisms involved in sensitization were analyzed using cytokine reporter mice, an adoptive cell transfer model, and gene knockout mice. Results: When exposed to peanut flour by inhalation, both BALB/c and C57BL/6 mice developed peanut allergy, as demonstrated by the presence of peanut-specific IgE antibodies and manifestation of acute anaphylaxis on challenge. A large number of follicular helper T (Tfh) cells were also detected in draining lymph nodes of allergic mice. These cells produced IL-4 and IL-21, and they more robustly promoted peanut-specific IgE production than T(H)2 cells did. Genetic depletion of Tfh cells decreased IgE antibody levels and protected mice from anaphylaxis, without affecting T(H)2 cells. Furthermore, peanut flour exposure increased lung levels of IL-1 alpha and IL-1 beta, and mice deficient in the receptor for these cytokines showed a significant decrease in Tfh cells compared with in wild-type mice. Conclusions: Tfh cells play a key role in peanut allergy, and the IL-1 pathway is involved in the Tfh response to peanut allergen exposure.