The pathogenesis of pleural plaques and pulmonary asbestosis: possibilities and impossibilities.

None of the various existing theories on the pathogenesis of pleura plaques (PP) is able to explain their peculiarities. Knowledge of physiology of the lung and pleura and in particular its lymphatic system as well as cellular activities when the cells are exposed to asbestos is necessary when discussing these problems. Short asbestos fibres when phagocytosed by macrophages will activate these cells to produce various substances, among them a factor that will stimulate fibroblasts to produce more collagen. Some of the small fibres will spread towards the visceral pleura of the lung, just like all inhaled dusts. Once in the visceral pleura, some of them will penetrate to the pleural space. There, they will follow the normal lymph flow from the pleural space, which is exclusively through the parietal pleura. Finally, in passing through the parietal pleura, a portion will remain in macrophages there, causing a low-grade stimulation of the submesothelial fibroblasts. After some decades, this will result in visible PP.