PPF - Is There a Cause of PPF?

There's a subset of patients with hypersensitivity and pneumonitis who go on to get a fibrotic variant. And so those patients, sometimes despite antigen removal or half the time we don't find the antigen, will fall under this category. In addition, there's the broad group of patients who have connective tissue disease or autoimmune related interstitial lung disease. A subset of them will develop progressive pulmonary fibrosis. Of those patients, some at higher risk, which include patients who have rheumatoid arthritis related interstitial Lung Disease.