Activation of the kinin-forming cascade on the surface of endothelial cells

Activation of the plasma kallikrein-kinin forming cascade takes place upon incubation with human umbilical vein endothelial cells. The mechanism by which initiation occurs is uncertain. Zinc-dependent binding of plasma proteins to gC1qR, cytokeratin 1, and perhaps u-PAR is requisite for activation to take place. We demonstrate here that during a 2 hour incubation time plasma deficient in either factor XII or high molecular weight kininogen (HK) fails to activate, as compared to normal plasma, but with more prolonged incubation, factor XII-deficient plasma gradually activates while HK-deficient plasma does not. Our data support both factor XII-dependent (rapid) and factor XII-independent (slow) mechanisms; the latter may require a cell-derived protease to activate prekallikrein and the presence of zinc ions and HK.