Also, the expression of midkine was increased in mouse lung tissue after bleomycin administration, while expression of collagen and α‐SMA and the pathological lung fibrosis score as well as TNF‐α and TGF‐β was lower in the lung tissue of Mdk KO mice, suggesting the involvement of midkine in the development of pulmonary fibrosis. The gene discussed is MDK; the disease is pulmonary fibrosis.