Later, using a low dose of bleomycin (10ug/mouse daily), the authors found that while wild-type C57BL/6J mice did not show signs of fibrosis at that dose, Mc1re/e mice, deficient for MC1 receptor on a C57BL/6J background, displayed obvious signs of fibrosis like increased skin thickness, collagen expression and levels of chemoattractant protein MCP-1, suggesting that the deficiency in Mc1r increases the susceptibility to develop bleomycin-induced fibrosis (194). This evidence concerns the gene CCL2 and fibrosis.