Secondly, we showed that TGF-β content increased in response to silica in the lungs of C57BL/6 but not BALB/c mice, confirming that TGF-β is more expressed in fibrosis-sensitive mouse strains than in fibrosis-resistant strains in response to fibrogenic stimuli [33-35]. This evidence concerns the gene TGFB1 and fibrosis.