Taken together, the proportion of proliferated Krt5 expressing AEC2s increased after CTGF administration, and Krt5 expressing AEC2s had higher proliferation potential than other AEC2s, indicating that CTGF treatment promoted the increase in Krt5 expressing AEC2s in mouse lungs after ALI and that Krt5 expressing AEC2s are an important subpopulation of stems/progenitors in lung regeneration after ALI. The gene discussed is KRT5; the disease is acute respiratory distress syndrome.