Effect on C2 activity of varying concentrations of anti-C2 antibodies from weeks 6 (A) and 11 (B) in the immunisation protocol. C2 (80 ng) was incubated with anti-C2 antibodies (0.125 to 1 mg/mL) from rabbits A1, A2, B1, B2, F1, F2, R1 and R2 collected at weeks 6 and 11 at pH 7.2 (15 min at 37 °C). Residual activity against Z-Phe-Arg-AMC was determined as described in Materials and methods. Each plot represents the mean of two experiments. Negative % change in activity indicates inhibition of enzyme activity.