SPP1 and pulmonary fibrosis: After secreted phosphoprotein 1 (SPP1) transfer, a marker of pulmonary fibrosis, to fibroblasts via M-sEVs, it activates the downstream cascade and leads to myofibroblast transition (FMT), promoting disease development, but the downstream reaction of SPP1 needs to be further studied (Huang et al., 2021b).