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Some human inhibitor antibodies interfere with factor VIII binding to factor IX
1American Red Cross, Holland Laboratory, Rockville, MD, USA.
Blood
|June 25, 1998
Summary
Hemophilia A patients developing inhibitors to factor VIII (fVIII) may have antibodies targeting the A3-C1 domains. These antibodies can block the interaction between fVIII and factor IXa, preventing blood clot formation.
Area of Science:
- Hematology
- Immunology
- Biochemistry
Background:
- Hemophilia A is a bleeding disorder caused by factor VIII (fVIII) deficiency.
- Therapeutic fVIII infusions can elicit inhibitory antibodies in ~23% of patients.
- Previous studies identified inhibitor epitopes in fVIII A2 and C2 domains.
Purpose of the Study:
- To investigate additional inhibitor epitopes within the fVIII light chain (A3-C1 domains).
- To elucidate the mechanism of fVIII inactivation by human inhibitor antibodies.
Main Methods:
- Inhibitor neutralization assays
- Immunoprecipitation assays using recombinant fVIII A3-C1 domains
- Factor IXa binding assays
- Chromogenic assays for factor Xa generation
Main Results:
- 17 of 18 inhibitor IgGs bound to the fVIII A3-C1 domain.
- Specific antibodies prevented factor IXa binding to the fVIII light chain.
- These antibodies inhibited factor Xa generation by the fVIIIa/fIXa complex.
Conclusions:
- The fVIII A3-C1 domains contain major inhibitor epitopes.
- Antibodies targeting these epitopes can inactivate fVIII by preventing fVIIIa/fIXa complex formation.
- This mechanism contributes to fVIII inactivation in hemophilia A patients with inhibitors.