Ultrastructural cytochemical analysis of oxygen radical-mediated immunoglobulin A immune complex induced lung injury in the rat.

Recent studies suggest that IgA immune complex induced lung injury in the rat is oxygen radical mediated. A cerium chloride (CeCl3) method was used to ultrastructurally analyze the in situ elaboration of H2O2 in IgA immune complex injured lungs. After induction of IgA immune complex lung injury, the lungs were instilled with a reaction buffer containing CeCl3 which forms an electron-dense precipitate when exposed to H2O2. Ultrastructural examination and x-ray microanalysis revealed electron-dense cerium deposits on the surfaces and in cytoplasmic vacuoles of alveolar macrophages located along damaged alveolar septae. Similar deposits were prominent on the luminal surfaces of injured pneumocytes, especially alveolar type II cells. No cerium-containing deposits were found in undamaged negative control lungs (IgA alone without antigen) or in lungs of rats that received IgA immune complexes in the presence of catalase. To further define the source of cerium-reactive products, monolayers of rat pulmonary alveolar epithelial cells were incubated with IgA complexes. Alveolar epithelial cells exposed to complexes produced no detectable H2O2 as measured by two spectrophotometric assays, and in the presence of CeCl3, exhibited negligible amounts of electron-dense material regardless of the presence or absence of catalase. The data corroborate indirect in vivo and in vitro studies which suggest that IgA immune complex induced lung injury is mediated by oxygen-derived metabolites produced by lung macrophages. Use of the CeCl3 method in intact rat lungs allows direct ultrastructural cytochemical analysis of H2O2 production in inflamed tissue.