Bronchoalveolar lavage fluid containing elastase most likely indicates production by which cell type?

• A. Ciliated epithelium
• B. Type I pneumocytes
• C. Type II pneumocytes
• D. Alveolar macrophage

Answer: (D)

Elastase is a protease released by inflammatory cells within the lung, and its presence in bronchoalveolar lavage fluid points to cells that reside in the alveolar space actively secreting proteases during inflammation. Among the listed cell types, alveolar macrophages are the primary source of elastase in the alveolar space; they become activated in response to infection, smoke, or particulates and release elastase (along with other proteases) to help defend and remodel tissue. However, excessive macrophage-derived elastase can damage elastin in the alveolar walls, contributing to conditions like emphysema. The other cells listed—ciliated epithelium, Type I pneumocytes, and Type II pneumocytes—do not secrete elastase as a normal function: ciliated epithelium mainly moves mucus, Type I cells are mainly for gas exchange, and Type II cells produce surfactant.