COMPARISON OF LUNG ALVEOLAR AND TISSUE-CELLS IN SILICA-INDUCED INFLAMMATION

The silicon dioxide mineral, cristobalite (CRS) induces inflammation involving both alveolar cells and connective tissue compartments. In this study, we compared lung cells recovered by whole lung lavage and by digestion of lung tissue from rats at varying times after 8 days of exposure to aerosolized CRS. Control and exposed rats were examined between 2 and 36 wk after exposure. Lavaged cells were obtained by bronchoalveolar lavage with phosphate-buffered saline. Lung wall cells were prepared via collagenase digestion of lung tissue slices. Cells from lavage and lung wall were separated by Percoll density centrifugation. The three upper fractions, containing mostly macrophages, were cultured, and the conditioned medium was assayed for effect on lung fibroblast growth and for activity of the lysosomal enzyme, N-acetyl-beta-D-glucosaminidase. Results demonstrated that the cells separated from the lung walls exhibited different reaction patterns compared with those cells recovered by lavage. The lung wall cells exhibited a progressive increase in the number of macrophages and lymphocytes compared with a steady state in cells of the lung lavage. This increase in macrophages apparently was due to low density cells, which showed features of silica exposure. Secretion of a fibroblast-stimulating factor was consistently high by lung wall macrophages, whereas lung lavage macrophages showed inconsistent variations. The secretion of NAG was increased in lung lavage macrophages, but decreased at most observation times in lung wall macrophages. No differences were found among cells in the different density fractions regarding fibroblast stimulation and enzyme secretion. These results support the view that it will be important to study inflammatory cells of the lung walls since they approximate other cells in the lung matrix and could be essential in the development of silicosis and interstitial fibrosis.