Crystalline Silica Promotes Rat Fibrocyte Differentiation in Vitro,and Fibrocytes Participate in Silicosis in Vivo

Objective The aim of this study was to investigate the effects of SiO2 on fibrocytes and whether fibrocytes participate in silicosis in vivo. Methods A macrophagocyte (AM)/fibrocyte coculture system was established, and AMs were treated with 100 μg/mL SiO2. Flow cytometry was used to detect the number of fibrocytes. Real-time PCR was performed to measure the expression of collagen Ⅰ, collagen Ⅲ, and α-SMA mRNA. The levels of collagen Ⅰ, collagen Ⅲ, and TGF-β1 protein were determined by ELISA. Immunohistochemical staining was performed to measure α-SMA protein expression. A rat silicosis model was induced by intratracheal instillation of SiO2. Lung histopathological evaluation was conducted using HE and Masson's trichrome staining after 1 and 9 weeks. The number of fibrocytes in peripheral blood or lung tissue of rat was detected by flow cytometry. Double-color immunofluorescence was applied to identify fibrocytes in the lung tissue. Results Peripheral blood monocytes were found to differentiate into fibrocytes in vitro in a time-dependent manner, and exposure to crystalline silica might potentiate fibrocyte differentiation. In addition, fibrocytes were able to migrate from peripheral blood to the lung tissue, and the number of fibrocytes was increased after SiO2 exposure. Conclusion Silica exposure potentiates fibrocyte differentiation, and fibrocytes may participate in silicosis in vivo.