CD8A and pulmonary fibrosis: Globally, we observed increased proportions of many immune cell types residing in the aged lung tissues (Supplementary information, Fig. S4a–d), including mast cells and plasmocytes (Supplementary information, Fig. S4a, b) that secrete cytokines and antibodies, respectively, likely contributing to increased age-related inflammation as well as COPD and idiopathic pulmonary fibrosis.45 In addition, CD8+ T cells that produce inflammatory cytokines and cytotoxic molecules in the pathogenesis of COPD were also elevated in the aged lung (Supplementary information, Fig. S4c).