Physiologists conduct a study to identify the protein constituents present in normal pulmonary secretions. They recruit 20 healthy men and women who do not take any medications and have no history of tobacco use. Bronchoalveolar lavage is performed, and the proteins in the fluids are isolated. A specific protein is found that can degrade the elastin present in the extracellular matrix. Which of the following cells are most likely producing this protein?

Question

Physiologists conduct a study to identify the protein constituents present in normal pulmonary secretions.  They recruit 20 healthy men and women who do not take any medications and have no history of tobacco use.  Bronchoalveolar lavage is performed, and the proteins in the fluids are isolated.  A specific protein is found that can degrade the elastin present in the extracellular matrix.  Which of the following cells are most likely producing this protein?

Quizplus · Accepted Answer

11ec160b_3a02_dc56_9249_afbc7b2e97b3_MD0001_00 Elastase is a neutral protease contained in macrophage lysosomes and in the azurophilic (primary) granules of neutrophils. Normally, elastase released from alveolar macrophages and infiltrating neutrophils is balanced by the presence of serum and tissue protease inhibitors. Neutrophil elastase is inhibited by serum alpha-1 antitrypsin, and macrophage elastase is inhibited by tissue inhibitors of metalloproteinases. Neutrophil and macrophage elastases can also degrade each other's (but not their own) inhibitors, augmenting their destructive capacity when both proteases are present. Excess protease activity is a major contributor to the development of both centriacinar and panacinar emphysema. (Choice B) The ciliated epithelium of the lower respiratory tract sweeps foreign particles and mucus toward the pharynx to promote mucociliary clearance. (Choice C) Club (formerly Clara) cells are nonciliated cells found predominantly in the terminal portions of the bronchioles. They secrete club cell secretory protein (which protects against airway inflammation and oxidative stress) and surfactant components (which prevent bronchiolar collapse). (Choice D) Goblet cells secrete mucin to help with mucociliary clearance. They are present in the epithelial lining of the trachea and bronchi but are not present in the more distal airways (ie, terminal bronchioles, respiratory bronchioles, alveoli). (Choice E) Type I pneumocytes constitute over 95% of the surface area of the alveoli. These end-differentiated squamous cells are not a major source of alveolar fluid secretory products. (Choice F) Type II pneumocytes secrete the major components of pulmonary surfactant, including phospholipids such as dipalmitoyl phosphatidylcholine and surfactant-associated proteins. Educational objective: Alveolar fluid contains neutral proteases (eg, elastases) that are derived from alveolar macrophages and infiltrating neutrophils. These proteases can cause destruction of terminal lung parenchyma (eg, emphysema) when secreted in excess or if left unchecked by deficient antiprotease activity. __________ References: Neutrophil elastase contributes to cigarette smoke-induced emphysema in mice. (http://www.ncbi.nlm.nih.gov/pubmed/14633606)

Physiologists Conduct a Study to Identify the Protein Constituents Present