title: Factor IX alloantibodies shorten the bovine thromboplastin coagulation time of normal human plasma.
abstract: We have previously demonstrated that neutralization of factor IX in normal plasma by heterologous antisera shortens the one stage prothrombin time determined with bovine thromboplastin. In this study, a similar effect of homologous antibodies was demonstrated. Addition of plasma from two patients with hemophilia B- and an acquired inhibitor to factor IX gave a shortening of the prothrombin time of plasma from normal persons, compared to the prothrombin time determined after addition of control plasma from a patient with hemophilia B- and no inhibitor. Addition of inhibitor plasma had a similar effect on the prothrombin time of plasma from four patients with hemophilia B+ and one patient with hemophilia BM, but had no effect on the prothrombin time of plasma from ten patients with hemophilia B-. Complexes between factor IX and the human inhibitor could be demonstrated both before and after the coagulation with bovine thromboplastin. These complexes were demonstrated as a factor IX antigen with a reduced electrophoretic mobility in crossed immunoelectrophoresis against a rabbit antiserum to factor IX. The results demonstrate that normal factor IX loses the ability to act as an inhibitor in the coagulation with bovine thromboplastin after having formed a soluble complex with a homologous antibody, although the factor IX molecules still have antigenic determinants which are free to react with the rabbit antibodies.
mesh_terms: D000818:Animals; D002417:Cattle; D005164:Factor IX / Q000037:antagonists & inhibitors / Q000276:immunology*; D002836:Hemophilia B / Q000097:blood; D006801:Humans; D007123:Immunoelectrophoresis, Two-Dimensional; D007518:Isoantibodies / Q000276:immunology*; D010314:Partial Thromboplastin Time; D011517:Prothrombin Time
chemical_list: D007518:Isoantibodies; D005164:Factor IX