TABLE 1.
Evaluation of the bactericidal titer and passive protection conferred by MAb Me-7 against serologically distinct meningococcal strains
| Meningococcal strain (serological classification) | Bactericidal titera
|
Level of bacteremia (CFU ± SD/ml of blood)b 5 h after challenge in:
|
% Reduction of bacteremia levels by MAb Me-7c | ||
|---|---|---|---|---|---|
| Rabbit serum | Human serum | Control mice injected with MAb P2-4 | Mice injected with MAb Me-7 | ||
| 4B (B:15:P1.−:L3) | 300 | 160 | 18,890 ± 8,872 | 4,688 ± 3,241 | 75 |
| 27B (B:2b:P1.2,5) | 10,000 | 600 | 46,800 ± 51,470 | 6,338 ± 7,494 | 86 |
| 44B (B:4:P1.12) | 950 | 120 | 46,710 ± 16,930 | 250 ± 370 | 99 |
| 58B (B:−:P1.10:L2) | 540 | 100 | 78,840 ± 51,060 | 10,160 ± 7,149 | 87 |
| 164B (B:15:P1.7,1.6) | 9,000 | 1,800 | 75,500 ± 82,390 | 12 ± 35 | 99 |
| 180B (B:4:P1.2,5:L1/3) | <10 | 40 | 57,760 ± 32,150 | 11,140 ± 8,893 | 81 |
| 187B (B:14:P1.−) | 2,250 | 1,800 | 28,730 ± 18,120 | 21 ± 43 | 99 |
| 608B (B:2a:P1.2:L3) | 4,500 | 1,500 | 19,230 ± 12,020 | 350 ± 558 | 98 |
| CHEO22 (B:15:P1.−)d | 200 | 100 | NDe | ND | ND |
| MCH88 (A:4:P1.10)d | <10 | <10 | 176,400 ± 90,490 | 164,500 ± 100,800NS | 7 |
| Z4734 (A:4:21:P1.16) | 2,500 | 1,400 | ND | ND | ND |
| Z4063 (A:4:P1.7) | 10,000 | 2,000 | 203,300 ± 98,520 | 7,188 ± 6,451 | 96 |
| 3C (C) | 2,500 | 900 | ND | ND | ND |
| 41C (C:2b:P1.2,5) | 8,000 | 3,000 | 83,210 ± 65,570 | 10,850 ± 8,062 | 87 |
The bactericidal titer of MAb Me-7 was determined to be the last dilution of antibodies which still reduced the numbers of CFU by at least 50% compared to the numbers of CFU in control wells containing an unrelated MAb and the appropriate amount of complement.
The control mice were injected intraperitoneally 18 h before the meningococcal challenge with either 400 μl of ascitic fluid or 50 μg of purified MAb Me-7 or control MAb P2-4. The level of bacteremia induced by each meningococcal strain was calculated from at least two separate experiments as the arithmetic mean CFU per ml of blood ± the standard deviation. Each value represents a mean of data obtained from at least eight animals. The Mann-Whitney U test for nonparametric analysis was used to compare the numbers of CFU recorded in control mice to the values obtained for mice injected with MAb Me-7. P < 0.05 for all Me-7 values except for the one marked “NS” (not significant). The bacterial inocula were adjusted to approximately 1,000 CFU for strains 4B, 44B, 58B, and 187B; to 2,500 CFU for strains 27B, 164B, and Z4063; and to 5,000 CFU for strains 608B, 180B, 41C, and MCH88.
The percentage of bacteremia was calculated relative to the control mice receiving MAb P2-4 as follows: [(mean CFU for control mice − mean CFU for Me-7-injected mice)/mean CFU for control mice] × 100.
The concentration of serum used in the in vitro bactericidal assay was reduced to 10%.
ND, not done.