Type II pneumocytes are preferentially located along thick elastic fibers forming the framework of human alveoli

Abstract

Type II pneumocytes were found to be preferentially located on thick elastic fibers which formed the main structural framework of the alveoli in humans. Eight lobes resected from eight patients with adenocarcinoma or atypical adenomatous hyperplasia and two lobes from two necropsies were examined. Four small specimens of normal lung tissue were obtained from each lobe fixed in a buffered formalin. Thick sections (200-300 microm) were stained with hematoxylin to contrast nuclei or with elastica staining to demonstrate elastic fibers and immunostained with an antibody against Thomsen-Friedenreich antigen after pretreatment with sialidase to visualize type II pneumocytes. Alveolar structure and the distribution of type II pneumocytes were examined in 3D reconstructions generated using a standard microscope, a personal computer and NIH-Image software. Nuclei including those of type I and type II pneumocytes and endothelial cells were distributed diffusely throughout the alveolar wall. Thick elastic fibers constructed the main structural framework of the alveoli and formed the sides of the polygonal alveoli. Type II pneumocytes were found to be linearly located along these thick elastic fibers. This previously undisclosed distribution of type II pneumocytes may be concerned with alveolar rapid movement.