Abstract
Factor IX antigen (IX:Ag) was studied by immunoradiometric assay (IRMA) in 24 cases of Hemophilia B using monoclonal anti-human Factor IX antibody (65-10). Precise measurements of Factor IX:Ag were possible for concentration as low as 0.01U/ml (1%) of that in normal pooled plasma. A good correlation (correlation coefficient=0.77) existed between the titers of Factor IX measured by clotting assay (IX:C) and IX:Ag assay among 15 normal adults. There was also a good correlation between the titers of IX:Ag measured by polyclonal anti-human IX antibody (Rabbit) and monoclonal antibody (65-10) in 15 normal adults (r=0.78). IX:Ag were absent (less than 0.01U/ml) with this assay in 15 Hemophilia B- patients. In 5 cases of Hemophilia B+ patients, the titers of IX:Ag with polyclonal antibody were 0.47±0.22U/ml, and that with monoclonal antibody (65-10) were 0.48±0.20U/ml.
However, in 4 BM patients, the dose responce curve was not parallel to normal pooled plasma. In these BM patients, prolonged Ox-brain prothrombin time was corrected by addition of monoclonal antibody (65-10).
These results suggest that the epitope detected by the monoclonal antibody (65-10) might be the abnormal part of the BM molecule which prolongs Oxbrain prothrombin time.
