Electron Microscopic Study of the Phagocytosis Process in Lung

Abstract

Diluted India ink was instilled into the nasal cavity of mice and the lungs of some animals were fixed with osmium tetroxide at various intervals after one instillation. The lungs of other animals were fixed after 4, 7, 9, 16, or 18 daily instillations.The India ink was found to be phagocytized almost exclusively by the free alveolar macrophages. A few particles are occasionally seen within thin portions of alveolar epithelium, within the "small" alveolar epithelial cells, or within occasional leukocytes in the lumina of alveoli. The particles are ingested by an invagination process of the plasma membrane resulting in the formation of intracellular vesicles and vacuoles. Ultimately large amounts of India ink accumulate in the cell, occupying substantial portions of the cytoplasm.The surfaces of phagocytizing macrophages show signs of intense motility. Their cytoplasm contains numerous particles, resembling Palade particles, and a large amount of rough surfaced endoplasmic reticulum. These structures are interpreted as indicative of protein synthesis. At the level of resolution achieved in this study the membranes of this reticulum appear as single dense "lines." On the other hand, the plasma membrane and the limiting membranes of vesicles and of vacuoles often exhibit the double-line structure typical of unit membranes (Robertson, 37).The inclusion bodies appear to be the product of phagocytosis. It is believed that some of them derive from the vacuoles mentioned above, and that they correspond to similar structures seen in phase contrast cinemicrographs of culture cells. Their matrix represents phagocytized material. Certain structures within this matrix are considered as secondary and some of these structures possess an ordered form probably indicative of the presence of lipid.The possible origin and the fate of alveolar macrophages are briefly discussed.

The Phagocytosis of Leucocytes

“…In this case the erythrocyte keeps almost the initial position. The above findings lead to a disagreement with reports which are supported by electron microscopic findings only, that a foreign body is trapped into the cytoplasm of cells by indentation, or invagination of the cell membrane.6),20), 23) It has been clarified that phagocytosis first requires the development of the pseudopod, and that it is greatly related with the adhesiveness and surface tension of the pseudopod.…”

Endothelial Permeability‐the Passage of Particles Into and Out of Diaphragmatic Lymphatics

“…This has never been seen although some hundreds of sections have been studied. In addition, the cells do not resemble macrophages [Palade, 1956;Essner, 1960;Karrer, 1960], nor are they similar to any of the usual connective tissue cells. Altschul [1954] and other workers, whom he cites, are of the opinion that endothelial cells can turn into macrophages.…”

Protein transport across the lung epithelial barrier

“…Other investigators showed that type I and type II cells take up ferritin and horseradish peroxidase into vesicles (47,98,123), whereas type II cells internalize SP-A from the alveolar space by receptormediated endocytosis (94). Both type I and type II cells have been shown to phagocytose foreign particles (22,54,63). Finally, clathrin-coated pits are present in alveolar type I and type II cells, whereas caveolincoated plasmalemmal vesicles (i.e., caveolae) are present in both pulmonary vessel endothelial cells and alveolar type I epithelial cells, suggesting possible transcytosis of proteins via these structural features (16,64,85).…”