Comparative O2-. responses of lung macrophages and blood phagocytic cells in the rat. Possible relevance to IgA immune complex induced lung injury

Abstract

IgA immune complex-induced lung injury in the rat is oxygen radical mediated and partially complement-dependent but develops fully after neutrophil depletion. The extent to which monocytes, lung interstitial macrophages, and alveolar macrophages may be involved in the development of lung injury in this model is unclear. To further understand the pathogenesis of IgA lung injury, we have examined the capacity of phagocytic cells isolated from different anatomic compartments of the lung to produce toxic oxygen-derived metabolites. [3H]Thymidine pulse labeling and autoradiography as well as in vivo phagocytosis studies were used to distinguish macrophages isolated from the alveolar and interstitial compartments. Lung interstitial macrophages were characterized ultrastructurally, cytochemically, and functionally. Interstitial macrophages were relatively uniform in size, had blunt pseudopodia, and contained almost no intracytoplasmic lamellar inclusions compared to alveolar macrophages. Similar to monocytes and alveolar macrophages, interstitial macrophages contained nonspecific esterase activity and exhibited the capacity to phagocytize latex and opsonized zymosan particles. Lung interstitial and alveolar macrophages incubated with IgA immune complexes, IgG immune complexes, or phorbol ester (PMA) produced similar amounts of O2-. in a dose-dependent manner. In contrast, peripheral blood neutrophils responded to IgG immune complexes and PMA but not to IgA immune complexes. Monocytes produced a small amount of O2-. in response to PMA but almost no O2-. in response to IgA or IgG immune complexes. These data are consistent with recent in vivo studies which indicate that IgA immune complex lung injury is neutrophil independent. The data provide direct in vitro evidence that lung interstitial and alveolar macrophages produce O2-. following incubation with PMA, IgA, or IgG immune complexes and may therefore contribute to the development of oxygen radical mediated lung injury.