Fig. 2.

Potential mechanisms of action of MSCs in the treatment of COVID-19 pneumonia. MSCs regulate the COVID-19-triggered cytokine storm and lung damage through its immunomodulatory and trophic functions. MSCs can secrete various anti-inflammatory cytokines, e.g., PGE2, TGF-β, IDO, and IL-10, to promote the differentiation of macrophages from the pro-inflammatory type M1 to the anti-inflammatory type M2, to reduce the neutrophil infiltration, and to regulate hyper-activated T cells. On the other hand, MSCs can secrete growth factors to inhibit fibrosis and to suppress epithelial/endothelial cell apoptosis and influx of alveolar fluid