 silica is a toxicant that can stimulate cells to produce various cellular products such as free radicals , cytokines , and growth factors . 
 silica and its induced substances may induce apoptosis to regulate the evolution of silica - induced inflammation and fibrosis . to examine this hypothesis , 
 groups of wistar male rats were intratracheally instilled with different doses of min - u - sil 5 silica ( silica , berkeley springs , wv ) . 
 ten days after the instillation , we obtained cells by bronchoalveolar lavage and placed them on slides by cytospin preparation . 
 the slides were stained with diff - quik ( lab aids , sydney , nsw , australia ) and examined under oil immersion . 
 a substantial number of cells with apoptotic features were identified in all silica - instilled rats and the apoptosis was confirmed by agarose gel electrophoresis . 
 the number of apoptotic cells was clearly related to silica dosage . 
 engulfment of apoptotic cells by macrophages was also noted . 
 neutrophil influx in silica - instilled rats could be saturated with the increase of silica dosage and the number of macrophages in different dose groups changed in parallel with the proportion of apoptotic cells . 
 fifty - six days after instillation , morphologically apoptotic cells could be identified in granulomatous cells of lung tissue from silica - instilled rats . 
 we conclude that intratracheal instillation of silica could induce apoptosis in both alveolar and granulomatous cells , and the apoptotic change and subsequent engulfment by macrophages might play a role in the evolution of silica - induced effects.imagesfigure 1.figure 3.figure 4.figure 5.figure 7.figure 8 . 
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