Summary
Development of antibodies (Ab) that inhibit the procoagulant function of factor VIII
(fVIII) seriously complicates the treatment of hemophilia A patients. It also causes
acquired hemophilia, a rare yet serious autoimmune disease. The design of effective
fVIII-specific tolerizing procedures will require elucidation of the role of the different
CD4+ T cell subsets that drive inhibitor synthesis. To examine the contribution of Th1
and Th2 cells in the anti-fVIII Ab response, we measured the concentration of Th1-
and Th2-driven anti-fVIII IgG subclasses in 17 patients with severe hemophilia A and
18 patients with acquired hemophilia. We found that both congenital and acquired hemophilia
patients had similar and comparable proportions of Th1- and Th2-induced anti-fVIII
Ab, suggesting a more important role of Th1 cells in the immune response to fVIII
than previously appreciated. The distribution of anti-fVIII IgG subclasses was stable
for periods of up to six months. More intense anti-fVIII Ab responses and higher inhibitor
titers correlated with a predominance of Th2-driven subclasses. In contrast, Th1-driven
anti-fVIII Ab were predominant in patients who had low anti-fVIII Ab concentrations,
even when this was the result of successful immune tolerance or immunosuppressive
therapy, which had caused drastic reduction or disappearance of inhibitors.
Thus, synthesis of Th2-driven inhibitors occurs when the anti-fVIII Ab response is
intense, while Th1 cells may be involved in the long-term maintenance of anti-fVIII
Ab synthesis.
Keywords
Th1 cells - Th2 cells - factor VIII - antibodies - hemophilia A - acquired hemophilia