Summary
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 Br, 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.
Keywords
Factor IX - Bovine thromboplastin - Alloantibodies
