Summary
1. Two patients with severe hemophilia B and an acquired inhibitor against factor
IX are described.
2. The inhibitors inactivate factor IX irreversibly. The speed of inactivation is
very fast and cannot slowed down by dilution of the inhibitor or by lowering of the
incubation temperature. Factor IX of serum is inactivated to a higher degree than
factor IX of plasma. Factor IX inhibitors are more sensitive to dilution than factor
VIII inhibitors.
3. The inhibitor protein is eluted from the Sephadex G-200 column with the G-peak.
On Chromatography on DEAE-cellulose two activity peaks are obtained.
4. Immunologically the inhibitors belong predominantly to the immune globulins of
the G-class, but it cannot be excluded that the activity is also associated with IgA.
As light chains kappa chains were found in one case.
