[Phagocytosis mechanisms of alveolar macrophages and granulocytes (author's transl)]

Concanavalin A distribution in polymorphonuclear leukocytes and alveolar macrophages during hyperoxia

Hyperoxia impairs cytoskeleton-dependent phagocytic functions in polymorphonuclear leukocytes (PMNs) and alveolar macrophages (AMs). To investigate the effect of different oxygen concentrations on the cytoskeleton, in particular the microtubule (MT) and microfilament (MF) system, the fluorescence pattern of Concanavalin A (Con A) receptors in AMs and PMNs was observed. Cells were obtained from guinea-pigs exposed to different oxygen concentrations. The exposure of guinea-pigs to oxygen concentrations of up to 50% induced in AMs and PMNs mainly spontaneous Con A capping, demonstrating an altered MT system. Oxygen tensions above 50% lead to an increased number of AMs and PMNs exhibiting a patchy Con A fluorescence distribution. Even in the presence of the microtubule-disrupting agent colchicine most AMs and PMNs were unable to form a Con A cap fluorescence distribution under these high oxygen tensions. This study demonstrates that the exposure of guinea-pigs to an oxygen concentration greater than 50% increases the relative number of AMs and PMNs demonstrating a patchy distribution of Con A. This patchy fluorescence pattern is associated with a severe cytoskeletal defect, i.e. MT and MF disruption. The various leukocyte function defects induced by hyperoxia, demonstrated in previous studies, are based on this MT and MF alteration in AMs and PMNs, representing an additional sepsis-promoting factor during hyperoxia.

In vivo binding and effects of concanavalin A (Con A) on rat and mouse pulmonary alveolar epithelial cells and macrophages

The binding and effects of inhaled or infused concanavalin A (Con A) preparations on rat and mouse pulmonary alveolar epithelium and macrophages were studied by a number of light- and electron-microscopical techniques. In comparison with BSA, inhaled Con A persisted considerably longer in the lung indicating the presence of Con A-receptors and mechanisms which prevent its rapid removal. In the lung periphery ferritin-labeled Con A was bound to type I and II pneumonocytes and macrophages. The density of binding sites was greater on type II than type I pneumonocytes. Within the time studied (up to 2 h) comparatively small amounts of the lectin were incorporated by endocytosis into the alveolar epithelium. The pulmonary macrophages bound and incorporated massive amounts of the lectin by endocytosis within 15 min. High doses of Con A lead to morphological deformation of the apical cytoplasmic zone of type II pneumonocytes and to a partial or complete collapse of the alveolar lumen. The possibility that the lectin may suppress surfactant secretion is discussed.

Effects of hyperoxia on phagocytosis

The development of bacterial infections is a common complication during treatment with high concentrations of oxygen. To study the effect of hyperoxia on phagocytes, the adherence, chemotaxis, ingestion rates, degranulation as well as the bactericidal activity were measured in alveolar macrophages (AMs) and polymorphonuclear leukocytes (PMNs) obtained from guinea pigs exposed to 85% oxygen. The animal exposure to a Fi O2 of 85% impaired the adherence to nylon-wool, the chemotactic activity and the phagocytic rate of paraffinoil-droplets of AMs and PMNs. In AMs the secretion of beta-glucuronidase upon stimulation with opsonized zymosan was also diminished. In addition, the bacterial activity of AMs and PMNs demonstrated a reduction of 50%. These phagocytic defects may be caused by cytoskeleton alteration, induced by the increase of oxygen derived metabolites, representing an additional sepsis promoting factor during hyperoxia.