Factor XI adsorption to surface: interaction of high molecular weight kininogen (HMWK) and a plasma adsorption inhibitor

High molecular weight kininogen (HMWK) plays an important role in surface activation of factor XI. These experiments were undertaken to evaluate the role of HMWK in factor XI adsorption to glass using purified 125I-labeled factor XI. Factor XI binding from Fitzgerald trait plasma was markedly reduced compared to normal plasma or other plasmas deficient in contact phase clotting factors; addition of exogenous HMWK to normal plasma levels corrected this defect. However, addition of higher concentrations of HMWK reduced factor XI binding. Addition of HMWK to normal plasma also reduced factor XI binding. In purified solutions, HMWK reduced factor XI binding to glass. Exposure of the glass to HMWK prior to addition of factor XI had no effect on factor XI binding. Factor XI adsorption from all plasmas was much less than from citrate-saline, and factor XI binding from both normal and Fitzgerald trait plasmas increased with increasing dilutions of the plasmas. These results lead to the conclusion that the direct effect of HMWK on factor XI is to reduce its ability to bind to glass by formation of a less adsorbable complex. The effect observed in Fitzgerald trait plasma, of increased factor XI binding on initial addition of kininogen, is an indirect effect achieved by counteracting another normal plasma activity which inhibits factor XI adsorption.