For the study on lung tissue, eligible subjects were IPF patients undergoing lung transplant surgery and from organ donors who died from non-pulmonary causes. For the study in clinic, subjects were IPF patients who had no other pulmonary disease other than IPF and the diagnosis of IPF was confirmed by lung biopsy or by clinical and chest CT findings. The control group consisted of subjects without respiratory symptoms or pulmonary diseases who were the household partner or spouse of an enrolled IPF subject and accompanied the IPF patient to outpatient clinic visits.