1999) and is thought to play an important role in tissue inflammation and repair (Muramatsu 2002). We have shown that expression of collagen and α‐SMA and the pathological lung fibrosis score were significantly lower in the lungs of Mdk KO compared with WT mice. Those findings indicate that midkine has a profibrotic property, which is in agreement with earlier findings generated in a mouse hyperglycemic nephrosclerosis model (Kosugi et al. 2007) and a heart pressure load model (Natsuizaka et al., 2014). The gene discussed is ACTA1; the disease is pulmonary fibrosis.