Fig. 1

Mechanisms of action of MSCs which can counteract viral infection. (1) Viral infection leads to tissue damage at the delicate blood-air barrier in the lung. The release of inflammatory cytokines initiates further tissue damage with (2) inflammatory T-cell proliferation and differentiation to Th-1 and Th-17s, (3) inflammatory white cell recruitment from the blood and tissues leading to further inflammation, creation of neutrophil NETS, fibroblast differentiation, oedema fluid accumulation and significant barrier disruption. MSCs have been demonstrated to act on several of the injurious processes that occur in infection such as (4) Release of cytokines and chemokines which promote anti-inflammatory innate and adaptive cell phenotypes, (5) release of factors which prevent the formation of NETS, reduce barrier disruption, and (6) prevent fibroblast differentiation and promote PMN apoptosis. (7) MSC IL-10 production and production from anti-inflammatory monocytes induces regulatory B and T cells and promotes tissue protection and repair, and MSC IDO production regulates inflammatory T-cell proliferation