TLR4 and injury: Liu et al. (2019) found that intravenous injection of BMSC-Exos into the rat model of acute lung injury could down-regulate TLR4 and NF-κB, inhibit TLR4/NF-κB and alleviate acute lung injury induced by ischemia-reperfusion by reducing apoptosis and inflammation. Similarly, Mao et al. (2021) discovered that continuous intravenous injection of BMSC-Exos for 5 days in mice with acute lung injury could inhibit cells apoptosis and promote the expression and relocation of connexin, restoring the barrier function of alveolar epithelial cells and protecting against pulmonary edema.