Mechanisms of Human Blood VII Activation in Plasma During Contact Activation, Clotting and Exposure to Cold
Factor VII(VII) is activated, giving shorter clotting times with tissue factor, when plasma is exposed to kaolin, is clotted or exposed to cold. The mechanisms involved were studied. Incubation of plasma with kaolin resulted in: No activation in XII deficiency plasma (dp), partial activation (2.5 fold) in Prekallikrein (PK) dp and High Molecular Weight Kininogen (HMWK) dp, and 4.5-9 fold activation in normal or other dp. Clotting plasma by recalcification resulted in: No activation with XII dp, HMWK dp, XI dp and IX dp, and 4-5 fold activation with VIII dp, X dp and V dp. The mechanism of cold promoted activation of VII in plasma was studied by adding purified 125-XII or 125I-IX to plasma before storage at 4° and observing the extent of their proteolysis (a measure of activation) from their radioactivity profiles on reduced Polyacrylamide gels following electrophoresis in the presence of SDS. Significantly greater 125I-IX and 125I-XII proteolysis was observed in plasma from 4 subjects whose VII activated in the cold, than in plasma from 5 subjects whose VII was not activated in the cold. Addition of anti-IX antiserum inhibited 50% of the observed cold activation of VII. Thus, with kaolin XIIa was the principal activator of VII; after clotting IXa was the principal activator and in cold activation both XIIa and IXa played roles.