Fig. 4. Effects of supernatants from silica-treated macrophages on the expression of miR-29b in NIH-3T3 and MRC-5 cells. Supernatants from silica-treated macrophages suppressed the expression of miR-29b in fibroblast cells, as measured by qRT-PCR. (a) NIH-3T3 cells were cultured in DMEM (NC) or the supernatants collected from Raw264.7 cells exposed to 0, 25, 50, 100 or 200 μg mL^–1 silica solution for 24 h. (b) MRC-5 cells were cultured in DMEM (NC) or the supernatants collected from Raw264.7 cells exposed to 0, 12.5, 25, 50 or 100 μg mL^–1 silica solution for 24 h. There was a significant and dose-dependent decline in the level of miR-29b in NIH-3T3 (a). In MRC-5 (b), miR-29b levels showed a statistically significant decline in the silica 50 μg mL^–1 group versus the silica 0 μg mL^–1 group. The data are presented as the means ± SD (n = 3). The significance of differences was determined by ANOVA followed by the Dunnett's test; *p < 0.05 versus the NC group, **p < 0.01 versus the NC group, ^p < 0.05 versus the silica 0 group, ^^p < 0.01 versus the silica 0 group.