The incidence of antibody responses to FVIII in E17 HLA-DRB1*1501 mice depends on the application route of FVIII and on the activation state of the innate immune system. Mice were treated with human FVIII at weekly intervals for 7 (A) or 8 (B-C) consecutive weeks. One week after the last dose, plasma samples were collected and analyzed by ELISA for the presence of anti-FVIII antibodies. (A) Comparison of the incidence of antibody responses after intravenous FVIII treatment of E17 HLA-DRB1*1501 mice (○) and conventional E17 mice expressing murine MHC class II (●). Each data point represents an individual mouse. (B) Comparison of the incidence of antibody responses after intravenous (○) and subcutaneous (▵) FVIII treatment of E17 HLA-DRB1*1501 mice. Each data point represents an individual mouse. (C) Comparison of the incidence of antibody responses after intravenous FVIII treatment of E17 HLA-DRB1*1501 mice in the absence (○; FVIII) or presence (□; FVIII + LPS) of a concomitant activation of the innate immune system. Each data point represents an individual mouse. (D) Correlation of neutralizing and total binding antibodies after intravenous (○) or subcutaneous (▵) FVIII or intravenous FVIII + LPS (□) of HLA-DRB1*1501 mice. Each data point represents an individual mouse.