Transgenic mice of sublines E and G differ in their antibody responses to human FVIII. Mice were treated with 8 weekly intravenous doses of human FVIII. Blood for antibody analysis and spleens for the analysis of antibody-secreting cells (ASC) were collected 1 week after the last dose. (A) Titers of anti–human FVIII IgG antibodies were detected by ELISA. Antibody titers were shown for individual mice. Anti-FVIII antibody-secreting cells (ASC) were analyzed by ELISPOT. Results obtained from a representative mouse are shown. Each spot corresponds to 1 ASC. (B) Plasma samples from 3 mice of each subline were analyzed for both titers of anti–human FVIII IgG antibodies by ELISA and FVIII inhibitor titers by Bethesda assay.