What Causes Idiopathic Pulmonary Fibrosis? What Causes Idiopathic Pulmonary Fibrosis? What Causes Idiopathic Pulmonary Fibrosis? What Causes Idiopathic Pulmonary Fibrosis? What Causes Idiopathic Pulmonary Fibrosis? What Causes Idiopathic Pulmonary Fibrosis?