Alloantibodies to factor IX in Haemophilia B characterized by crossed immunoelectrophoresis and enzyme-conjugated antisera to human immunoglobulins.

Incubation of factor IX with non-precipitating alloantibodies to factor IX gives rise to soluble complexes between factor IX and the alloantibodies. These complexes appear as a factor IX molecule with a reduced mobility in crossed immunoelectrophoresis against a rabbit antiserum to factor IX. This factor IX immunoprecipitate was used for the study of alloantibodies to factor IX from five patients with severe haemophilia B (antibody titres 0.1--800 units/ml plasma). Incorporation of antiserum to k light chains or lambda light chains of human immunoglobulin G in an intermediate gel in crossed immunoelectrophoresis gave a reduction of the factor IX precipitin arc, indicating the presence of immunoglobulin G alloantibodies containing both k and lambda light chains in complex with factor IX. Incubation of the factor IX immunoprecipitate with peroxidase-conjugated antisera to the same immunoglobulins, and staining for peroxidase activity, confirmed the presence of immunoglobulin G containing both types of light chains in the factor immunoprecipitate. It is concluded that all five alloantibodies were polyclonal immunoglobulin G antibodies. The technique had the advantage that the light chain types of low-titre antibodies could be determined, and it may be suitable for further characterization of alloantibodies to factor IX if antibodies to immunoglobulin subclasses are available.