Major Cell Types of the Lower Respiratory Tract

Reff; Histology for Pathologist, 3rd Edition

Cell Type Features Function(s) Location Histochemical and/or Immunohisto-chemical Staining Ciliated Columnar, cuboidal, ciliated bronchial lining cells; each cell has approximately 250 cilia at the apical surface, and each cilium is approximately 6 µm long Proximal transport of mucous stream (mucociliary escalator) Bronchi and bronchioles Epithelial markers2 Goblet Columnar mucus-secreting cells; contain mucous glycoprotein, which discharges apically Contribute to airway mucus Bronchi (more numerous proximally); small numbers in bronchioles Epithelial markers2, histochemical mucin stains, MUC5 Basal Short cells with relatively little cytoplasm; oriented along the basement membrane; do not reach the luminal surface of the epithelium Precursor cell of ciliated and goblet cells Bronchi; rare in bronchioles Epithelial markers2 Neuroendocrine (Kulchitsky or K cells) Basal-oriented cells with numerous dense-core (neurosecretory) granules; single or in groups (neuroepithelial bodies), the latter near sites of airway bifurcation Specific functions not known; considered part of the diffuse neuroendocrine system Bronchi; rare in bronchioles Chromogranin-A, synaptophysin, NCAM Brush Found infrequently at all levels of the airways; some have termed these type III pneumo-cytes; they are named for a brush border of microvilli approximately 2 µm in length Thought to be involved in fluid absorption or chemoreceptor function All airways Ultrastructurally identified Serous Identical to serous cells in the minor salivary gland tissues Produce secretion of lower viscosity than that from mucous cells Primarily bronchioles Lysozyme Neuroendocrine bodies Clusters of 4–10 neuroendocrine cells adjacent to the subepithelial basement membrane Unknown; hypotheses include chemoreceptor, tactile receptor, vasoconstrictive functions Bronchi, bronchioles, and alveoli Chromogranin-A, synaptophysin Oncocytic Eosinophilic mitochondrial-rich cells in submucosal gland ducts Ion secretory functions Submucosal glands Epithelial markers2 Squamous Stratified squamous epithelium is an abnormal metaplastic replacement of normal pseudostratified respiratory epithelium Protective, reparative Bronchi, bronchioles, and occasionally alveoli Epithelial markers2, cytokeratin 5/6 Clara Columnar nonciliated bronchiolar cells; protuberant apical cytoplasm with large, ovoid electron-dense granules; comprise the majority of nonciliated bronchiolar cells Secretory functions contributing to the mucous pool and maintaining extracellular lining fluid; progenitor for other bronchiolar cells; role in surfactant Predominantly in bronchioles CC10, diastase-resistant PAS-positive apical granules Type I alveolar pneumocyte Large, flat, squamous alveolar lining cells; cover some 93% of alveolar surface area; incapable of division Provide a thin air-blood interface for gas transfer Alveoli Epithelial markers2, caveolin, and aquaporin Type II alveolar pneumocyte Columnar alveolar lining cells; microvillous surface; synthesize and secrete surfactant (lamellar ultrastructural inclusions); capable of division Maintain alveolar stability; progenitor for type I pneumocytes Alveoli Epithelial markers2, surfactant protein C Minor salivary tissue: Serous, Mucous, Ductal Cells Submucosal minor salivary glands identical to other sites with serous and mucinous acinar cells that secrete into the ducts, which empty at the mucosal surface Secretion and contribution to airway mucous stream Bronchial submucosa Epithelial markers2, histochemical stains for mucin, Alcian blue/PAS Smooth muscle Bundled smooth muscle surrounds the conducting airways to the level of the alveolar ducts Contraction of the airway Peripheral in the airway and external to the cartilage in bronchi Muscle specific actin, smooth muscle actin, desmin, vimentin