2. Pulmonary fibrosis (PF) is characterized by abnormal repair of the respiratory epithelium. Various diseases may result in PF such as infections, autoimmune (connective tissue disorders), sarcoidosis, hypersensitivity pneumonitis, pneumoconiosis, histiocytosis X, lymphangioleiomyomatosis LAM etc. In many situations a cause effect relationship cannot be identified and the disease is idiopathic IPF.