Figure 6.

The mechanism of action of proteases to inhibit the allergen and other microbe attacks. Proteases are released in response to allergens due to a microbial attack that causes severe damage to epithelial cells by disrupting the junctional proteins [192]. Allergen proteases bind to protease-activated receptor 2 (PAR2) by cleaving the fibrinogen into the fibrin cleavage products (FCPs) that activate the toll-like receptor 4 (TLR4) and ILC2s. These ILC2s lead to activation of NF-kB and excess production of reactive oxygen species (ROS). It activates epithelial cells to release the pro-Th2 cell chemokines and cytokines that activated the instruct immature dendritic cells (iDCs). P-glycoproteins (P-gp) helps in removing the protease inhibitors in epithelial cells that cause the suppression of allergen proteases [190,193]. This figure is reproduced from Wu et al. [190] (Attribution 4.0 International, CC BY 4.0).