# Microbial sensing through the non-canonical inflammasome modulates airway type 2 immunity

## TL;DR

This study shows how airway cells sense bacteria through a special immune pathway that can trigger allergic inflammation, offering new insights into asthma treatment.

## Contribution

The study reveals that the non-canonical inflammasome in airway epithelial cells links microbial sensing to type 2 immune responses.

## Key findings

- Intracellular LPS activates caspase-4-dependent pyroptosis, leading to IL-33 release and MAPK signaling.
- Protease allergens enhance LPS-induced pyroptosis via Orai1-mediated calcium signaling.
- Caspase-4 deletion reduces type 2 immune responses in a mouse model of allergen challenge.

## Abstract

Airway epithelial cells serve as critical sensors of both microbes and allergens, orchestrating immune responses through damage-associated molecular patterns including IL-33. Common aeroallergens induce type 2 inflammation through protease activity and pore-forming mechanisms that trigger epithelial IL-33 secretion and MAPK signaling. While microbial pattern receptors such as caspase-4 (which detects intracellular LPS) similarly generate membrane pores via the non-canonical inflammasome, it remains unknown whether these receptors can engage the same downstream epithelial IL-33 release and MAPK activation pathways.

Using human airway epithelial cell models, we examined caspase-4-dependent pyroptotic signaling downstream of intracellular LPS, including gasdermin D cleavage, IL-33 release, and MAPK-dependent transcriptional responses. We assessed the modulatory effect of protease allergen co-exposure on LPS-induced pyroptosis and interrogated the role of Orai1-mediated calcium signaling in vitro. In a mouse model of protease allergen challenge, we evaluated innate type 2 immune responses following genetic deletion of caspase-4 (formerly caspase-11). LPS preparations from multiple bacterial species were tested for capacity to engage the non-canonical inflammasome in epithelial cells, and publicly available human asthma datasets were analyzed for airway expression of caspase-4 and gasdermin D.

Intracellular LPS activated caspase-4-dependent pyroptotic signaling, resulting in gasdermin D cleavage, IL-33 release, and MAPK-dependent transcriptional responses. Protease allergen exposure enhanced LPS-induced pyroptotic responses through Orai1-mediated calcium signaling in vitro. Genetic deletion of caspase-4 attenuated innate type 2 immune responses in the mouse protease allergen challenge model. LPS preparations from different bacterial species demonstrated variable capacity to engage the non-canonical inflammasome. Analysis of human asthma datasets revealed increased airway expression of both caspase-4 and gasdermin D in asthmatic patients relative to healthy controls.

These findings identify the epithelial non-canonical inflammasome as a pathway capable of linking microbial pattern recognition to IL-33-dependent type 2 responses. This work establishes a mechanistic framework for understanding how bacterial sensing machinery may intersect with allergic inflammation during pathophysiological conditions, and suggests that caspase-4 signaling could represent a therapeutic target in asthma.