C5aR antagonist augments anti-C7 inhibition of whole-blood killing of meningococci. Whole blood from 4 subjects vaccinated with MenB-4C was tested for killing activity against 2 serogroup B strains, Ohio University and Quebec, in the presence or absence of complement inhibitors. Data are geometric mean CFU per milliliter (ranges) from 2 experiments with blood from subjects 007 and 011, and CFU per milliliter from 1 experiment each for subjects 009 and 010. (A,C) CFU in blood at time 0 and after 3 hours of incubation in the absence of inhibitor. (B,D) CFU per milliliter in blood after 3-hour incubation with C5aR antagonist (red bars) or ant-C7 mAb (yellow bars), or anti-C7 + C5aR antagonist (red hatched yellow bars). The combination of the C5aR antagonist and anti-C7 mAb blocked killing of both strains to a greater extent than the anti-C7 mAb alone (P < .04 by paired t test on log-transformed data).