CCN2 and idiopathic interstitial pneumonia: PF-ILD: Progressive fibrosing interstitial lung diseases; CTGF: connective tissue growth factor; FVC: forced vital capacity; DLCO: diffusing capacity for carbon monoxide; IPF: idiopathic pulmonary fibrosis; NSIP: nonspecific interstitial pneumonia; CTD-ILD: interstitial lung disease associated with connective tissue diseases; SD: standard deviation.