Autoantibody to factor VIII that has less reactivity to factor VIII/von Willebrand factor complex.
To determine the difference in reactivity of factor VIII (FVIII) inhibitor to FVIII/von Willebrand Factor (vWF) complex and FVIII free of vWF, an autoantibody to FVIII light chain was tested. A patient (1-3) suffered from autoimmune hemolytic anemia with autoantibody to FVIII. Epitope specificity of the patient's IgG (I-3 IgG) was shown to be the C2 domain of FVIII light chain (2170-2332) by Western blotting using recombinant FVIII deletions expressed in Escherichia coli. The inhibitory effect on FVIII procoagulant activity (VIII:C) of I-3 IgG was tested against a conventional FVIII concentrate; Haemate P, a monoclonal antibody-purified FVIII concentrate; Hemofil M, and a recombinant FVIII (rFVIII); Kogenate. I-3 IgG showed only 1.3 BU/mgIgG for Haemate P, in contrast to 20 BU/mgIgG for both Hemofil M and Kogenate. The ratio of VIII:C/vWF:Ag in Haemate P and Hemofil M was 1/3.43 and 1/0.01, respectively, while Kogenate did not contain vWF. The inhibitory effect of the I-3 IgG was then compared with Kogenate and its complex with vWF. The inhibitory effect was decreased against the rFVIII by forming a complex with vWF from 22 BU/mgIgG to 0.5 BU/mgIgG. Fab from the I-3 IgG had the same effect. In addition, vWF showed a protective effect on FVIII inactivation by the I-3 IgG in a dose dependent manner. Fifty-nine percent of residual VIII:C was retained in the presence of 8 U/ml of vWF after 1 hr incubation with I-3 IgG. These results suggested that vWF could compete with the I-3 IgG for binding to FVIII.
Amano
K
K
Department of Clinical Pathology, Tokyo Medical College, Japan.
Arai
M
M
Koshihara
K
K
Suzuki
T
T
Kagawa
K
K
Nishida
Y
Y
Fukutake
K
K
D000328:Adult; D000743:Anemia, Hemolytic / Q000276:immunology* / Q000378:metabolism; D001323:Autoantibodies / Q000276:immunology* / Q000494:pharmacology; D005169:Factor VIII / Q000037:antagonists & inhibitors / Q000276:immunology*; D005260:Female; D006801:Humans; D007147:Immunoglobulin Light Chains / Q000276:immunology; D014841:von Willebrand Factor / Q000037:antagonists & inhibitors / Q000276:immunology*
D001323:Autoantibodies; D007147:Immunoglobulin Light Chains; D014841:von Willebrand Factor; D005169:Factor VIII