Characterization of the immune response in mice with hemophilia A.

(A) Sixteen mice injected with 0.2 μg fVIII were bled after each of 5 consecutive injections, and Ab titers were determined by ELISA. The closed circles represent Ab concentrations for individual mice, and the line is the mean of Ab titers after each bleed. (B) Anti-fVIII IgG1 (gray) and IgG2a (white) were determined after 5 injections of fVIII in plasma samples of 15 mice. Results are expressed as end-point titers, the dilution factor that gave a signal greater than 2 SDs above the background, a 1:10 dilution of naive hemophilic plasma. (C,D) T cells and peritoneal macrophages were pooled from 2 mice injected 5 times with fVIII (gray) or 2 naive mice (white) and cultured with 100 nM fVIII in X-vivo medium. After 2 days (IL-2) and 5 days (IL-4, IL-10, and IFN-γ), cytokine ELISAs were performed from culture supernatants. The cytokine results are expressed as the mean and SD of duplicates.