The alanine polymorphism is weakly detected by monoclonal antibody A-1. All mice in the figure are naive (untreated) mice. The left side of the figure shows that neither the polyclonal antibody (poly) nor monoclonal antibody A-1 demonstrates background factor IX reactivity in the knockout mouse. In the right side of the figure the first bar shows the level of factor IX detected by the polyclonal antibody in juvenile R333Q-hFIX mice (age 4 weeks). The second bar shows the level detected by the polyclonal antibody in adult mice (age 6 weeks). The third bar demonstrates the low cross-reactivity of A-1 for the alanine polymorphism of the factor IX expressed in the R333Q-hFIX mice (age 6 weeks). Data represent the mean ± SD.