Concordantly, we further identified an autoimmune-prone sub-cluster unique to aged club cells (Fig. 5D, Additional file 2: Fig. S5M, S5N, and Additional file 10: Dataset 8) and enriched in COPD lungs (Fig. 5A), for which antigen presentation via MHC I and IFN-γ-mediated signaling pathway were remarkably activated (Fig. 5E), whereas cell proliferation and the FGF receptor signaling pathway were suppressed (Additional file 2: Fig. S5O and S5P) compared to other aged club cells. The gene discussed is IFNG; the disease is chronic obstructive pulmonary disease.