Effect of complement inhibitors on survival of meningococci in whole blood of individual vaccinated adults. (A) Serogroup B strain H44/76. (B) Serogroup C strain 4243. At time 0, ∼3600 CFU/mL N meningitidis were added to blood (gray bars). In the absence of a complement inhibitor, blood from all 12 subjects had sterile cultures (blue bars) by 3 hours. In contrast, addition of eculizumab (ECZ; anti-C5, orange bars) completely blocked bacterial killing of both strains. ACH-4471 (complement factor D inhibitor, green bars) had no effect (sterile culture) on killing of the serogroup B strain H44/76 in 7 of 12 subjects, and no effect on killing of the serogroup C 4243 strain in 10 of 12 subjects (see “Results”).