The role of macrophages as a source of reactive oxygen intermediates in pulmonary inflammation associated with pathogenic dusts. Final report on Colt Foundation Contract CF/07/84

The reactive oxygen intermediates are a class of toxic leukocyte products which have been shown to be important in experimental pulmonary inflammation and which are implicated in human pulmonary inflammation. The present study was funded by the Colt Foundation to examine the potential importance of the reactive oxygen intermediates in experimental pulmonary inflammation caused by pathogenic mineral dusts, in the laboratory rat. Three representative bronchoalveolar leukocyte populations were chosen for use in the study (i) control (98% alveolar macrophages) (ii) 16 h post C. parvum instillation ( 90% neutrophils) (iii) 5 d post quartz instillation ( equal proportions dusted macrophages and neutrophils). In the first part of the study the control, inert dust (titanium dioxide) and the two pathogenic mineral dusts (quartz and chrysotile asbestos) failed to provoke a respiratory burst, with reactive oxygen intermediate release, when added to^ the leukocyte populations in vitro. The effect was not simply due to toxic effects of the dust on the leukocytes. In the second part of the study the inflammatory leukocyte “”populations were found to cause detachment, without lysis, of A549 alveolar epithelial cells following co-culture in vitro. This effect could be generally stimulated by adding pathogenic dust to the co-cultures but the greatest stimulation was produced with addition of quartz to epithelial cell/quartz bronchoalveolar cell co-cultures. Blocking studies revealed the detaching activity to be mediated by protease and reactive oxygen intermediates. The ability of the control and inflammatory populations to proteolytically degrade the extracellular matrix components fibronectin, laminin and denatured collagen was assessed and the inflammatory cells were found to have substantially more activity than the control cells. In the third part of the study control alveolar macrophages cultured for 48 hours on collagen gels were found to generate substantially less of an oxidative burst than the same cells cultured on plastic; the effect was not due to toxicity in the collagen-cultured population.The results of the study show that reactive oxygen intermediates are likely to accumulate in mineral dust inflamed lung only because of the increased number of cells and the presence of soluble trigger and not as a consequence of mineral dust triggering. The study has also confirmed the likely importance of leukocyte proteases in epithelial injury and extra-cellular matrix re-modelling during inflammation. “”