Polymorphism of normal factor IX detected by mouse monoclonal antibodies.

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Abstract
Hemophilia B is an X-chromosomal recessive disease due to deficiency of coagulation factor IX. Three monoclonal antibodies against factor IX were prepared and used to develop immunoradiometric assays (IRMA) of factor IX antigen (IX-Ag). IX-Ag was measured in 65 normal individuals with 1 IRMA based on polyclonal anti-IX antibodies and 2 IRMA based on 3 monoclonal anti-IX antibodies. One of the monoclonal antibodies differed in specificity since it neutralized < 50% of the clotting activity of factor IX (IX-C), whereas the other 2 monoclonal antibodies neutralized 80-95%. When the former antibody was used as the solid phase in IRMA, 2 groups of normal individuals were distinguished: group A with measurable IX-Ag, and group B without demonstrable IX-Ag. There were no differences between the groups either in IX-C or in IX-Ag measured with polyclonal antibodies. A subgroup comprising only women could be distinguished in group A, in whom intermediate IX-Ag concentrations were found. Family studies showed the group B variant of normal factor IX to be transmitted according to the pattern of X-linked recessive inheritance. The allelic frequency of group A was 0.66, and that of group B was 0.34.