Blood clots and TAM receptor signalling in COVID-19 pathogenesis.

We suggest that the exuberant blood clotting and immune hyper-reaction seen in patients with COVID-19 may be exacerbated by depletion of the same regulator. This agent is protein S, which is both an anticoagulant in the blood coagulation cascade and an activating ligand for the immunosuppressive TAM family of receptor tyrosine kinases. In this Comment, Greg Lemke and Gregg Silverman propose that the excessive blood clotting and immune activation seen in severe COVID-19 may be mechanistically linked through protein S, a ligand for the immunosuppressive TAM receptor family.