Summary
Two subpopulations of antibodies were isolated from rabbit polyclonal antiserum directed
against human factor IX: one against the Ca(II)-dependent conformation of factor IX
and one against the Ca(II)-independent conformation of factor IX. The two subpopulations
were used for the development of immunoradiometric assays (IRMA’s) for factor IX:
Ca(II)Ag and factor IX: NonCa(II)Ag respectively. Ranges for the concentration of
factor IX:Ca(II)Ag and factor IX: NonCa(II)Ag were established in plasmas of healthy
volunteers, patients treated with oral anticoagulants and hemophilia B patients. In
the group of patients using oral anticoagulant therapy a progressively reduced ratio
of factor IX:Ca(II)Ag to factor IX: NonCa(II)Ag was observed with increasing intensity
of oral anticoagulant treatment. Variant factor IX molecules from hemophilia B patients
. (CRM-, CRMRed and CRM+) with a defective Ca(II) binding or defective conformational transition induced by
Ca(II) binding, were identified. These defects are absent in variant factor IX molecules
from one hemophilia Bm patient and from patients with hemophilia B Leyden.
Key words
Factor IX antibodies - Calcium dependency - Oral anticoagulation - Hemophilia B
