We therefore used a chemical proteomics approach to discover that SfA primarily interacts with the endoplasmic reticulum–resident (ER-resident) peptidyl-prolyl cis-trans isomerase cyclophilin B (PPIB gene and PPIB protein) in live cells and shows subsequent secretion of PPIB from the ER to the extracellular space, which may play a role in the inhibition of collagen folding by SfA in myofibroblasts in vitro, in vivo, and in lung fibrotic tissue from patients with IPF. The gene discussed is PPIB; the disease is idiopathic pulmonary fibrosis.