ATF6 and idiopathic pulmonary fibrosis: Western blot (the same samples used in STING protein Western blot) showed that the ER stress markers, ATF6, IRE1α, binding immunoglobulin protein (also known as GRP78), X-box protein 1 (XBP1, the downstream molecular of the IRE1α pathway), and C/EBP homologous protein (CHOP) were upregulated significantly in the PBMCs from the AE-IPF group compared to the IPF and HC groups (all p < 0.05, Figure 3A; Figure S5 in Supplementary Material), indicating the activation of ER stress and UPR in the PBMCs of the AE-IPF group.