ABSTRACT
After treatment with factor (F) VIII concentrate a significant number of patients
with hemophilia A develop inhibitory antibodies that neutralize FVIII. Epitope mapping
revealed that antibodies bind to selected regions within the A2, A3, and C2 domains
of FVIII. Anti-A2 and anti-A3 antibodies interfere with assembly of FVIIIa with FIXa,
whereas anti-C2 antibodies impede the interaction of FVIII with phospholipids. The
immunologic mechanisms underlying inhibitor development in hemophilia A have not been
fully elucidated. FVIII is recognized by the immune system as a foreign antigenic
substance that evokes the T cell-dependent formation of high-affinity antibodies.
Clonal analysis of B cell responses in hemophilia A patients has given further insight
into the epitope specificity and molecular characteristics of FVIII inhibitors. Costimulatory
blockade of FVIII-reactive T cells in a mouse model for hemophilia A has suggested
new approaches for treatment of inhibitor patients. In this article, recent studies
on the immunobiology of FVIII inhibitors are summarized and discussed with reference
to their potential impact on treatment and prevention of immune responses in patients
with hemophilia.
KEYWORD
Factor VIII - inhibitors - hemophilia