Loss of Twist1 in mesenchymal collagen-producing cells increases bleomycin-induced pulmonary fibrosis by up-regulating Cxcl12 expression in mice [325], highlighting the crucial role of the CXCR4-CXCL12 axis in IPF pathogenesis. The gene discussed is CXCL12; the disease is idiopathic pulmonary fibrosis.