Factor XI

Factor XI. Factor XI is a Hver-synthesized glycoprotein that circulates in a zymogen form as a dimer. It is converted to its active serine protease form by Factor Xlla in the presence of high molecular weight kininogen. Calcium is not required for this activation step. 

Congenital deficiency of Factor XI is a relatively rare coagulopathy that has been reported as both an autosomal dominant and autosomal recessive trait. This deficiency state occurs predominantly in the Jewish population. Most patients with this deficiency state remain asymptomatic until trauma or surgery is encountered. Spontaneous hemorrhage is rare in this population. 

HK it can interact with surface-bound factor XII on an adjacent particle thereby disseminating the reaction [25, 28]. As a result the effective kallikrein/factor XII ratio is increased in the presence of HK [25], Finally, in plasma, HK can displace other adhesive glycoproteins such as fibrinogen from binding to the surface [29]. In this sense, HK, like factor XII and prekallikrein, is also a coagulation cofactor because it is required for the generation of kalUkrein (a factor XII activator) as well as the activation of factor XI. 

Thompson RE, Mandle R Jr, Kaplan AP Studies of 30 binding of prekallikrein and factor XI to high molecular weight kininogen and its light chain. Proc Natl Acad Sci USA 1979 76 4862-4866. 

Tail JF, Fujikawa K Primary structure requirements 31 for the binding of human high molecular weight kininogen to plasma prekallikrein and factor XI. J Biol Chem 1987 262 11651-11656. 

Wiggins RC. Bouma BN. Cochrane CG. Griffin JH Role of high-molecular-weight kininogen in surface-binding and activation of coagulation factor XI and prekallikrein. Proc Natl Acad Sci USA 1977 74 4636-4640. 

Type of Hemorrhage Desired Plasma Factor VIII Level (% of Normal) Desired Plasma Factor XI Level (% of Normal) Duration of Therapy (Days)... 

XI Posttraumatic bleeding Prolonged aPTT Normal PT Normal thrombin time Specific factor XI assay... 

Von dem Borne P. A. K., Meijers J. C. M., Bouma B. N. Feedback activation of factor XI by thrombin in plasma results in additional formation of thrombin that protects fibrin clots from fibrinolysis. Blood 1995 86, 3035 -42. 

Activated factor XII leads to the activation of factor XI in turn, activated factor XI, along with Ca++ ions and factor IV, leads to activation of factor IX. Activated factor IX, along with Ca++ ions, factor VIII, and PF3, leads to the activation of factor X. From the point of factor X activation, the extrinsic and intrinsic mechanisms follow the same pathway to fibrin formation. 

Figure 2.4 Response values obtained from experiments carried out at different levels of the factor Xi and the assumed response surface.

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