APOA2 and hypersensitivity pneumonitis: A set of three most significantly upregulated proteins (HBB, CRP and SERPINA1) and four most significantly down-regulated proteins (APOA2, AHSG, KNG1 and AMBP) were selected for verification in validation cohorts (n = 80, 20 healthy controls, 20 IPF patients, 20 hypersensitivity pneumonitis patients and 20 sarcoidosis patients) using ELISA.