The diagnosis variables of rheumatoid arthritis and interstitial lung disease were used for the correlation analysis: age, anti-CCP, rheumatoid factor (RF), C-Reactive protein (CRP), forced vital capacity (FVC), expiratory volume in the first second (FEV1), and the PAD2 and PAD4 protein levels in serum and bronchoalveolar lavage (RA-ILD patients). The gene discussed is CRP; the disease is interstitial lung disease.