Serum of untreated, immunized or arthritic BALB/C and C57BL/6 mice was tested with ELISA for antibodies against ACPA: CCP (a) and MCV (b). Time points: healthy untreated, 4 days after first immunization (−17 days), 4 days after second immunization (−10 days), acute phase (4 days after induction), transition phase (10 days after induction), early chronic phase (3 weeks after induction), and late chronic phase (8–9 weeks after induction). White bars indicate mean values for BALB/c, grey bars for C57BL/6 samples. Data is representative of two independent experiments with 8–15 animals per time point and group. (c) The presence of pertussis toxin during immunization influences ACPA levels. BALB/c mice were immunized according to the ACIA scheme with or without PTx and levels of anti-CCP antibodies compared at different disease stages. Time points: 4 days after second immunization (−9 days), acute phase (4 days after induction), transition phase (10 days after induction), early chronic phase (3 weeks after induction). Mice were immunized according to the ACIA scheme with either PTx (circles) or PBS instead of PTx (triangles). Statistics: Mann–Whitney-U-test (n.s.: not significant, *P<0.05, **P<0.01, ***P<0.001).