Ultrastructure of the Nonciliated Bronchiolar Epithelial (Clara) Cell of Mammalian Lung. III. A Study of Man with Comparison of 15 Mammalian Species

TLDR

Nonciliated bronchiolar epithelial cells are defined by two morphologic features: abundant agranular endoplasmic reticulum and numerous membrane‑bound ovoid granules. The study examined lobectomy specimens from three nonsmoking humans and comparable lung tissue from fifteen mammalian species, fixing the tissue by airway infusion at constant pressure, embedding selectively, and analyzing bronchioles by electron microscopy. Human cells displayed many membrane‑bound granules (≈6 per cell) and granular ER but lacked agranular ER, and comparison with fifteen species revealed three distinct morphological categories, indicating substantial interspecies variability.

Abstract

AbstractTwo morphologic characteristics have been used to define the nonciliated bronchiolar epithelial cell: (1) abundance of agranular endoplasmic reticulum (AER) and (2) numerous membrane-bound ovoid granules. In this study, we examined lobectomy specimens from three nonsmoking humans: one male (9.5 yr) and two females (62 and 43 yr) for comparison with lung specimens from mammalian species used as experimental models in lung research. Following fixation by airway infusion at constant pressure (20 cm), lung tissue was processed by a selective embedding technique and bronchioles of known anatomic location were studied by electron microscopy. Nonciliated bronchiolar epithelial cells of man contained numerous membrane-bound granules (averaging 6 per cell) in the apical cytoplasm and abundant granular endoplasmic reticulum (GER). AER was not observed. Granules averaged 0.3 μm in diameter and contained a fine granular matrix and parallel tubular arrays. After comparing these features in man with those of fifteen other species, we concluded that there is a great deal of interspecies variability in the cellular morphology of the nonciliated epithelial cell of distal conducting airways in mammalian lung. Three categories of this cell were observed: (1) with abundant granules and AER, characteristic of rabbit, guinea pig, rat, hamster, mouse, horse, sheep, and pig; (2) with abundant granules of GER, but no AER, characteristic of man and other primates; and (3) with few granules, little AER, and abundant glycogen, characteristic of steer, dog, cat, and ferret.