Demonstration of Complexes Between Factor IX And IGG Antibodies from Hemophilia B Patients

Plasma from three patients with hemophilia B- and an acquired inhibitor to factor IX (titres: 5 U/ml, 0.73 U/ml and 0.32 U/ml) were incubated with purified factor IX and submitted to crossed Immunoelectrophoresis against a rabbit antiserum to factor IX. A heterogenous precipitin arc was seen instead of the homogenous precipitin arc seen when a control plasma from a patient with hemophilia B- and no acquired inhibitor was used for the incubation. Human IgG antibodies were demonstrated in the cathodal part of the precipitin aros. This was achieved by incubation of the agarose gels, after the electrophoresis, with a peroxidase conjugated rabbit antiserum to human IgG. The IgG antibodies from the two patients with the highest inhibitor titre contained both kappa and lambda light chains, and were thus of a polyclonal nature. It is concluded that IgG antibodies from low-tltred as well as high-titred inhibitor plasmas form complexes with factor IX. The detection of IgG in complex with factor IX may be a sensitive technique for the detection of low-titred inhibitors to factor IX.