AbstractInhaled aeroallergens can directly activate airway epithelial cells (AECs). Exposure to cockroach allergens is a strong risk factor for asthma. Cockroach allergens mediate some of their effects through their serine protease activity; protease activity is also a major contributor to allergenicity. The Th2 cytokine interleukin‐13 (IL‐13) induces upregulation of the eosinophil chemotactic factor CCL26. CCL26 induces eosinophil migration in allergic inflammation. In this work, we studied the effect of cockroach proteases on IL‐13‐induced effects. Immersed cultures of the human bronchial epithelial cell line BEAS‐2B and air‐liquid interface (ALI) cultures of primary normal human bronchial epithelial (NHBE) cells were stimulated with IL‐13, Blattella Germanica cockroach extract (CE), or both. IL‐13‐induced genes were analyzed with qRT‐PCR. IL‐13 induced upregulation of CCL26, periostin, and IL‐13Rα2 in bronchial epithelial cells which were decreased by CE. CE was heat‐inactivated (HICE) or pre‐incubated with protease inhibitors. HICE and CE preincubated with serine protease inhibitors did not prevent IL‐13‐induced CCL26 upregulation. CE‐degraded IL‐13 and specific cleavage sites were identified. CE also decreased IL‐4‐induced CCL26 upregulation and degraded IL‐4. Other serine proteases such as bovine trypsin and house dust mite (HDM) serine proteases did not have the same effects on IL‐13‐induced CCL26. We conclude that CE serine proteases antagonize IL‐13‐induced effects in AECs, and this CE effect is mediated primarily through proteolytic cleavage of IL‐13. IL‐13 cleavage by cockroach serine proteases may modulate CCL26‐mediated effects in allergic airway inflammation by interfering directly with the pro‐inflammatory effects of IL‐13 in vivo.