Development of the pulmonary acinus in fetal rat lung: a study based on an antiserum recognizing surfactant-associated proteins.

In this study on the development of the pulmonary acinus in fetal rat lung use was made of an antiserum, rabbit anti-mouse, that recognizes the type II alveolar epithelial cell or its precursor (a cuboidal cell lacking multilamellar bodies) by the presence of a cell-specific antigen. This serum had already been used in studies on mouse-lung development in our laboratory. Immunoblotting experiments showed that this serum reacts with surfactant-associated proteins in the pellet fraction of rat-lung lavage fluid having molecular weights of about 26,000, 32,000, and 38,000 daltons. In adult and fetal rat-lung homogenates the antiserum reacts with proteins with apparent molecular weights of about 40,000 and 42,000 daltons, probably also surfactant-associated proteins. No reaction with serum proteins was seen. Use of this antiserum in immuno-incubations of frozen sections of lungs of 15- to 21-day-old rat embryos showed that the type II epithelial cell or its precursor first appears on day 16 in embryos weighing 349-398 mg. Our results indicate that in the rat - as in the mouse - the bronchial and respiratory portions develop from morphologically and immunologically different parts of the tubular system in the fetal lung. The basic structure in the genesis of the pulmonary acinus is a tubule, called the acinar tubule, which is lined by the type II epithelial cell or its precursor.