Residues Glu2181-Val2243 contain a major determinant of the inhibitory epitope in the C2 domain of human factor VIII.
The human blood coagulation factor VIII C2 domain (Ser2173-Tyr2332) contains an epitope recognized by most polyclonal inhibitory anti-factor VIII alloantibodies and autoantibodies. We took advantage of the differential reactivity of inhibitory antibodies with human and porcine factor VIII and mapped a major determinant of the C2 epitope by using a series of active recombinant hybrid human/porcine factor VIII molecules. A series of five C2-specific human antibodies and a murine anti-factor VIII monoclonal antibody, NMC-VIII/5, inhibited a hybrid containing a substitution of porcine sequence for Glu2181-Val2243 significantly less than human factor VIII. In contrast, four of the five patient antibodies and NMC-VIII/5 inhibited a hybrid containing a substitution of porcine sequence for Thr2253-Tyr2332 equally well as human factor VIII. Thus, a major factor VIII inhibitor epitope determinant is bounded by Glu2181-Val2243 at the NH2-terminal end of the C2 domain. Because C2 inhibitors block the binding of factor VIII to phospholipid and von Willebrand factor, for which binding sites have been localized to Thr2303-Tyr2332, these results imply that the segment bounded by Glu2181-Val2243 also is involved in these macromolecular interactions.
Healey
J F
JF
Emory University, Atlanta, GA; Holland Laboratory, American Red Cross, Rockville, MD, USA.
Barrow
R T
RT
Tamim
H M
HM
Lubin
I M
IM
Shima
M
M
Scandella
D
D
Lollar
P
P
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology / Q000494:pharmacology; D003429:Cross Reactions; D000939:Epitopes / Q000737:chemistry* / Q000276:immunology; D005169:Factor VIII / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism; D006467:Hemophilia A / Q000097:blood; D006801:Humans; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D010743:Phospholipids / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000276:immunology; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D013329:Structure-Activity Relationship; D013552:Swine; D014841:von Willebrand Factor / Q000378:metabolism
D000911:Antibodies, Monoclonal; D000939:Epitopes; D046911:Macromolecular Substances; D010743:Phospholipids; D011993:Recombinant Fusion Proteins; D014841:von Willebrand Factor; D005169:Factor VIII