Epithelial cell membrane perforation induces allergic airway inflammation.

Abstract

Allergens that induce allergic airway inflammation are highly diverse, but they commonly activate type 2 immune responses^1,2. Airway epithelial cells are crucial in allergen sensing^3-5. However, the shared features among diverse allergens that elicit similar innate responses, and their epithelial detection mechanisms, remain poorly defined^1,2,6-9. Here we identify pore-forming proteins as one of the common stimuli of allergic airway inflammation and reveal their immune-activation mechanisms. Using the prevalent mould allergen Alternaria alternata as a model, we established an in vitro system to investigate type 2 innate immune sensing. A six-step biochemical fractionation identified Aeg-S and Aeg-L as the core immune-stimulatory components. Biochemical reconstitution and cryo-electron microscopy reveal that these proteins form 16- to 20-mer transmembrane pore complexes. Their cooperative perforation acts as a bona fide type 2 immune adjuvant to support antigen-specific T helper 2 and immunoglobulin E responses. Genetically engineered A. alternata strains that lack pore-forming activity do not induce allergic responses in mice. Furthermore, pore-forming proteins from various species, despite structural and membrane target differences, are sufficient to trigger respiratory allergies. Perforations in airway epithelial cells initiate allergic responses through two mechanisms: one triggers IL-33 release, and the other involves Ca²⁺ influx, which activates MAPK signalling and type 2 inflammatory gene expression. These findings provide insight into how type 2 immune responses detect common perturbations caused by structurally diverse stimuli. Targeting downstream signalling of epithelial perforation may open new avenues for treating respiratory allergies.