A Mechanism for the Induction of Type 2 Immune Responses by a Protease Allergen in the Genital Tract

The genital mucosa is a barrier that is constantly exposed to a variety of pathogens, allergens, and external stimuli. Although both allergen exposure and parasite infections frequently occur in the genital area, the mechanism by which immune responses-particularly type 2 immunity-are induced has rarely been studied in the genital mucosa. Here, we demonstrate the induction of T helper type 2 (Th2) immunity in the genital mucosa in response to a model allergen, the protease papain. Intravaginal papain immunization induced type 2 immunity in a manner that was dependent on protease activity and the estrous phase of the mice. In addition, IL-33 was released from the vaginal epithelia after intravaginal papain immunization, leading to the activation of type 2 innate lymphoid cells (ILC2s). Moreover, the IL-33-MyD88 (myeloid differentiation primary response gene 88) signaling pathway was critical for the induction of type 2 immunity. We also found that Th2 differentiation in response to intravaginal papain treatment requires a specific dendritic cell (DC) subset that is controlled by interferon regulatory factor 4 (IRF4). These findings suggest that type 2 immunity is induced by a unique mechanism in the genital tract, which is an important, but often overlooked, barrier surface.