F11 and COVID-19: Henderson et al. identified that in comparison with healthy individuals, COVID-19 patients had elevated levels of protease-serpin complexes, such as complexes of FXIIa:C1-INH, kallikrein:C1-INH, FXI:C1-INH, and FXIa:α-antitrypin, along with higher levels of single proteases, such as FXI and cleaved/non-cleaved high molecular weight kininogen (45).