Progressive loss of the macrophage respiratory burst in oxygen toxicity

The respiratory burst of rat alveolar macrophages stimulated by a variety of agents declines as a function of time of exposure to hyperoxia. Previous studies have evaluated this effect in terms of the stimulated O(2) production of a population of cells. The present study was designed to determine whether this decline is due to a "turning off" of the respiratory burst activity of some cells within the alveolar macrophage population or a general suppression of the activity of all cells. The phorbol myristate acetate (PMA) initiated respiratory burst of individual rat alveolar macrophages was monitored using the reaction of nitroblue tetrazolium (NBT), which results in the formation of a precipitate on active cells. The formazan staining was evaluated using black and white photographs of the cells and comparison to a scale constructed from photographed cells of four differing intensities of staining. Frequency distributions indicated that when the respiratory burst capability in the population of alveolar macrophages is impaired approximately 50% by oxygen exposure and/or culture in plastic vessels with artificial media, there is a gradual shift in NBT reduction rather than an "all or nothing" mechanism, in which the distribution would have reflected a shift from darkly stained cells to the very lessened or negligible staining observed at the end stage of oxygen toxicity.