Immunological Studies Of Human Factor XI

Abstract

Human Factor XI was purified from normal plasma, using ionic exchange chromatography on DEAE-sephadex at pH 8.3, and SP-sephadex at pH 5.3., followed by an affinity chromatography column of insolubilized high M.W. kininogen. Factor XI adhered to this column and was step eluted with 0.5 M NaCl. This rapid method gives highly purified Factor XI with yields of 15-20%. Antibodies were raised in goats against purified Factor XI. A trace of a contaminating antibody was removed by absorption with a Factor XI-depleted γ-globulin fraction. When tested by double immunodiffusion, one precipitin line was observed against normal plasma, which showed a reaction of identity with the line obtained against purified Factor XI. No line was observed against plasma of a patient with Factor XI deficiency. The antiserum specifically inhibited the Factor XI clotting activity of normal plasma.Factor XI, which is a γ-globulin (pI ∼ 9) that does not migrate during immunoelectrophoresis (IEP), forms reversibly complexes with high MW kininogen, an a-globulin. Complex formation under conditions of IEP at pH 8.4 was shown in purified mixtures by crossed IEP using anti Factor XI and by rocket IEP. Rocket IEP showed no Factor XI antigen in Factor XI deficient plasma. Factor XI antigen in normal plasma was increased by addition of high MW kininogen, suggesting that part of the Factor XI present in normal plasma is not complexed to high MW kininogen. These results show that IEP studies of Factor XI and high MW kininogen are influenced by complex formation.