DDIT3 and idiopathic pulmonary fibrosis: In normal lung, the distribution of LR-MSC in the alveolar interstitium was sparse without significant CHOP expression (Fig. 1D), while in IPF lung, LR-MSC in fibrotic foci showed a higher CHOP level, which indicated that the LR-MSC suffered from ER stress during pulmonary fibrosis.