Using ELISA and immunofluorescence staining, it was seen that downregulation of KDELR2 caused a reduction in MUC5AC levels in both bronchial epithelium and BALF (Figure 4B,C,E), which supported the hypothesis that KDELR2 might participate in MUC5AC hypersecretion in COPD. This evidence concerns the gene MUC5AC and chronic obstructive pulmonary disease.