COLLAGEN-PRODUCING MESOTHELIAL CELLS IN ADRIAMYCIN-INDUCED PLEURITIS IN RAT

By the microautoradiographic method using ³H-proline, collagen production by mesothelial cells was investigated in adriamycin-induced pleuritis in rats. In subpleural granulation tissue formed at 4 to 7 days after the intrapleural injection of adriamycin, proliferating fibroblasts and primitive mesenchymal cells were most intensely labeled, and abundant deposition of collagen and acid mucopolysaccharides were demonstrated about these cells. It is thus concluded that these subpleural mesenchymal cells are mainly responsible for the fibrosing process. Labeling was also observed in some reactive mesothelial cells and macrophages free-floating in the pleural exudate. Several ultrastructural differences between labeled mesothelial cells floating in the fluid and lining the pleural surface were confirmed, suggesting a change in ability to synthesize collagen during mesothelial desquamation. It seems likely that these labeled mononuclear cells in the effusion, attached to the pleural wound surface, support fibrosis performed by underlying collagen-synthesizing mesenchymal cells. Pleural fibrosis disappeared by 10 days, when mesothelial regeneration was almost complete. Probably this change may be due to fibrinolytic activity caused by regenerative mesothelial cells derived from subpleural mesenchymal cells.