A persistent low titer IgG factor IX inhibitor (0.8–2.3u/ml) has been previously described
in an 11 year old boy with severe hemophilia B-. Since the disappearance of factor IX antigen (IXAGN) following Konyne(R) infusion was markedly delayed (
60 hr) compared to factor IX clotting activity (T 8 hr) (Blood 48:977, 1976), a search for circulating factor IX antigen-inhibitor
complexes was undertaken. The inhibitor binds firmly to staphlococcal protein A –
Sepharose 4B (SPA-Sepharose) but may be eluted in the IgG 1, 2, and 4 fraction with
3M NaSCN. SPA-Sepharose chromatography of post-infusion plasma (IXAGN 2.7u) from the patient with the inhibitor showed IXAGN (0.5u) in the IgG 1, 2, and 4 fraction, whereas IXAGN was not found in that fraction of chromatographed samples of post infusion plasma
from non-inhibitor patients with hemophilia B- or B+. Using a highly specific antibody to factor IX, two dimensional Immunoelectrophoresis
of purified factor IX or normal plasma showed a single symmetrical fast moving peak.
When an equal volume of inhibitor plasma was added to either factor IX or normal plasma
a second, slower moving component was also seen. Two dimensional Immunoelectrophoresis
of plasma obtained from the patient 45 minutes after infusion showed both the slow
and fast components. The presence of IXAGN in the IgG 1, 2, and 4 peak after SPA-Sepharose chromatography and the demonstration
of 2 components on two dimensional Immunoelectrophoresis indicates the presence of
circulating factor IX antigen-inhibitor complexes in the plasma of this patient following
the infusion of a factor IX concentrate.
