The ultrastructure of rat type II pneumocytes: effects of age, sex, and strain

The ultrastructure of epithelial cells of the distal lung

This review has focused on the structural and functional characteristics of those epithelial cells that line the walls of the lower respiratory bronchioles, alveolar ducts, and alveoli. In all, five cells types were considered: Clara cells, types I, II, and III pneumocytes, and alveolar macrophages. In addition, a very brief mention of the structure and influence of the basement membrane in alveolar development and repair was included, as well as a brief review of the role of epithelial cells in response to selected deleterious influences. No attempt was made to extend this review to cover the structure and functions of the epithelial lining of the conducting portions of the respiratory system, or the exciting and expanding complexities and interrelationships of the septal stroma. Since the volume of literature encircling this subject has virtually exploded during the last 15 years, it becomes almost impossible to review all reports. However, attempts were made to be selective in citations. Insofar as future developments are concerned, much remains to be understood concerning (1) the responses of all cell types to cytotoxic influences, including their respective abilities to repair induced damage, (2) cell-cell and cell-extracellular matrix relationships in response to injury, (3) the uniqueness of the basement membrane in the lung in controlling permeability and gaseous exchange, (4) the role(s) of alveolar macrophages in response to injury and their relationships to the septal macrophage population, (5) the aberrations in the respective cell types that can give rise to neoplastic growth, and (6) the role of the immune system in responding to the general defense of the lung. Indeed much has been learned in the past 2 decades, and it is expected that a review of this sort 1 or 2 decades hence will elucidate many of the functions and structural modifications of the lung.

Characterization of rat alveolar type II cells in vitro by immunological, biochemical, and morphological criteria

Using an anti-rat surfactant apoprotein antiserum which specifically reacts with cytoplasmic structures in alveolar type II cells on histopathology sections of rat lung, we have examined the immunoreactivity of pulmonary type II cells in vitro. Single cell suspensions of lung tissue were prepared from male Fischer 344 rats by intratracheal elastase digestion according to standard published methods. Cytocentrifuged preparations of the resulting cell suspensions revealed that approximately 40% of the cells stained positive for surfactant apoprotein using an immunoperoxidase staining technique. Without further cell fractionation steps, the cell suspensions were plated at colonial densities in growth medium. The cells that attached after 24 hours of incubation and at daily intervals were analyzed for surfactant apoprotein immunoreactivity as well as for proliferation, morphology, and phospholipid biosynthesis. The percentage of immunopositive cells increased with time from 75% at day 1 to 94% at 4 days after plating. This increase was paralleled by a linear increase in the number of immunopositive cells, which expanded into cell colonies. During the initial 5 days in vitro, the immunopositive cells retained their epithelial morphology and contained cytoplasmic osmiophilic bodies. Phospholipid biosynthesis by the isolated lung cells was analyzed and the data revealed that the rate of incorporation of 14C-choline into phosphatidylcholine increased with time in culture. These studies indicated that the anti-rat surfactant apoprotein antisera can be used to identify and quantitate functional alveolar type II cells in vitro. Thus the specific antisera may facilitate studies of type II cells undergoing various environmental alterations both in vivo and in vitro.