Proximal and terminal complement pathway activation byN meningitidisin plasma from the patient and his mother. The formation of C3bc and sTCC, reflecting proximal complement activation and terminal pathway activation, respectively, in plasma of the homozygous factor D-deficient patient B (□), his heterozygous mother (▪), and the median ± interquartile range (IQR) of 4 healthy controls (▦). The plasma was incubated for 1 hour at 37°C without stimulus or with 10⁸/mL meningococci in the absence or presence of recombinant factor D or anti–factor D, as indicated. The experiment was repeated once, yielding virtually identical results (not shown).