XBP1 and idiopathic pulmonary fibrosis: We examined the associations between cell stress marker expression and lung function parameters and found that greater expression (i.e., labeling by immunofluorescence) of both XBP1% and BiP% (UPR) (Figure 2A,B) and cleaved caspase-3% (apoptosis) (Figure 2C) in IPF lungs was associated with reduced FEV1, FVC, TLC, and RV, respectively.