The ability of inflammatory bronchoalveolar leucocyte populations elicited with microbes or mineral dust to injure alveolar epithelial cells and degrade extracellular matrix in vitro.

Inflammatory cells are recruited to the parenchyma of the lung in a range of conditions where they are considered to have the ability to exert damaging effects on elements of the alveolus. The injurious effects of rat bronchoalveolar-derived inflammatory cells on an alveolar Type II epithelial cell line were therefore assessed. Inflammatory populations produced by intratracheal injection of Corynebacterium parvum or quartz caused non-lethal detachment injury to the epithelial cells on co-culture whereas control bronchoalveolar cells had no effect on epithelial cells. The pathogenic mineral dusts quartz and chrysotile asbestos caused increased detachment injury when added to co-cultures of epithelial cells and bronchoalveolar leucocyte populations; neither titanium dioxide, a control mineral dust, nor zymosan were active in this respect. Detachment injury was particularly marked when quartz was added to co-cultures of epithelial cells and inflammatory bronchoalveolar cells from quartz treated lung. On the basis of anti-protease and anti-oxidant studies, the detachment injury was found to be mediated by protease alone in the case of quartz cells and protease plus oxidant in the case of C. parvum cells. The two inflammatory bronchoalveolar cell populations were found to have increased proteolytic activity, compared to control bronchoalveolar cells, as shown by increased ability to degrade fibronectin, laminin and denatured collagen. Inflammatory bronchoalveolar cells therefore have the potential to attack elements of the septal extracellular matrix as well as to compromise the integrity of the alveolar epithelium.