A 54 year old man is admitted to the hospital with cough and dyspnea, which over a period of years has led to marked respiratory embarrassment and cyanosis. Chest x-ray film of the lungs showed bilateral lower lobe ground-glass infiltrates. Wedge biopsy of the lung demonstrates air spaces filled with macrophages containing lipid, periodic acid-Schiff (PAS)-positive granules, and lamellar bodies. There is an accompanying interstitial pneumonitis, hyperplasia of the septal lining epithelial cells, and desquamation of epithelial cells into alveolar. The lamellar bodies within the macrophages are composed of which of the following?

The disease is desquamative interstitial pneumonitis (DIP), which is an idiopathic process related to idiopathic interstitial fibrosis. DIP may respond to steroid therapy but may also progress to end-stage lung disease. The lamellar (layered) bodies within macrophages contain surfactant derived from type II pneumocytes. Amyloid is deposited extracellularly and is not pa of the DIP process. Calcitonin is found in medullary carcinoma of the thyroid. Fibrin deposition can be pa of the DIP process, but occurs as eosinophilic extracellular deposits, rather than as intracellular lamellar bodies. Ref: Levitzky M.G. (2013). Chapter 2. Mechanics of Breathing. In M.G. Levitzky (Ed), Pulmonary Physiology, 8e.