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K Koshihara, J Qian, P Lollar and LW Hoyer
Holland Laboratory, American Red Cross, Rockville, MD 20855, USA.
Porcine factor VIII has been used successfully to treat factor VIII
inhibitor patients whose plasmas have minimal cross-reactivity to porcine
factor VIII. However, some inhibitor plasmas do inhibit porcine factor
VIII, and the extent of procoagulant inhibition often increases after
treatment with porcine factor VIII. Because there is no information about
the porcine factor VIII epitopes with which these antibodies react, we have
compared the immunoblot and enzyme-linked immunosorbent assay (ELISA)
reactivities with porcine and human factor VIII for 20 inhibitor plasmas
(11 from hemophilia A patients and 9 autoantibodies). Immunoblots
identified binding to porcine factor VIII for only 2 of the 12 plasmas from
patients who had not received porcine factor VIII, but this reactivity
could not be predicted from the inhibitor titer to porcine factor VIII.
Immunoblot reactivity with porcine factor VIII was detected for 7 of 8
inhibitor plasmas from patients who had been previously treated with
porcine factor VIII, and the strength of this reactivity was generally
related to the inhibitor titer. Of the 5 plasmas that were immunoblot
positive with the porcine factor VIII A2 domain, 4 had inhibitor titers
greater than 45 Bethesda units when tested with porcine factor VIII,
whereas only 1 of 15 of the other plasmas had this level of inhibitor
activity with porcine factor VIII. In contrast, immunoblot reactivity to
the porcine factor VIII A1 domain did not correlate with the antiporcine
VIII inhibitor titer. We also determined the effect of preincubation with
human or porcine factor VIII on immunoblot reactivity. In one case,
immunoblot reactivity with porcine factor VIII was absorbed with porcine,
but not human, factor VIII, which is consistent with antibody formation
after treatment with porcine factor VIII. In no cases did human factor VIII
reduce the reactivity of inhibitor plasmas with the porcine A1 domain,
suggesting that these antibodies are directed at unique porcine factor VIII
determinants. The reactivity to porcine A2 in 2 plasmas probably
represented cross-reactivity of similar A2 determinants, because it was
absorbed by both human and porcine factor VIII. Although the ELISA assays
with porcine factor VIII detected antibodies in some plasmas that could not
be identified by inhibitor assay or immunoblot, the level of ELISA
reactivity was generally consistent with the titers of the other assays.
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| Copyright © 1995 by American Society of Hematology Online ISSN: 1528-0020 | |||||||||