Allergen source-derived proteases compromise epithelial barrier function by degrading TJ proteins, facilitating allergen accessibility to DCs. Enzymatically active allergens can activate PAR to induce TSLP. TSLP induces immediate innate immune functions in DCs, leading to recruitment of inflammatory cells. TSLP triggers the maturation of DCs, so they migrate to mediastinal lymph nodes. Induction of DCs to upregulate OX40L by TSLP promotes Th2 responses. PAR also upregulates production of MMP-9, which degrades tight junction proteins. Thus, impairment of airway epithelial barrier function and activation of epithelial cells are involved in the pathogenesis of inflammation mediated by allergen source-derived proteases.