KRT5 and acute respiratory distress syndrome: The proportion of proliferated Krt5+SPC+ cells in AEC2s increased after CTGF administration, and they had stronger proliferation potential than Krt5−SPC+ cells, indicating that CTGF administration promoted the increase in Krt5 expressing AEC2s in mouse lungs after ALI and that Krt5+SPC+ cells are an important subpopulation of stems / progenitors in lung regeneration after ALI.