MUC5AC and Cowden syndrome 1: 2007). As mucin 5AC and periostin are both important biomarker proteins, we validated our gene expression findings for MUC5AC and POSTN using ELISA (Fig. 2B). Mucin 5AC protein expression appeared to be lowered upon IL‐13 exposure cessation; however, 5 days seems insufficient time to return protein levels to baseline expression levels. Additionally, periostin protein could only be detected in ALI‐PBEC that were continuously exposed to IL‐13 without the presence of CS (Fig. 2B).