FIG. 4.

Antibodies against Fbs protect mice against lethal infection with Fbs-expressing GBS strains. (A and B) Passive immunization. C3H/HeN mice were injected i.p. with 0.1 ml of rabbit anti-Fbs serum. Control mice received preimmune rabbit antiserum. The mice were challenged i.p. 4 h later with an ∼LD₉₀ of log-phase bacteria. (Due to interexperimental variation, the survival was higher than 10% in some cases.) Two Fbs-expressing GBS type V strains, 10/84 and SBL10, were used, as indicated. Deaths were recorded daily for a period of 7 days, and the final ratios (number of surviving mice to number of mice challenged) are indicated. The P values were calculated by the Fisher exact test. (C and D) Active immunization. C3H/HeN mice were vaccinated with highly purified protein Fbs. Control mice received PBS. The vaccinated mice were challenged i.p. with an ∼LD₉₀ of log-phase bacteria. Strains used were the same Fbs-expressing type V strains as used for the passive immunization experiments, and data are presented in the same way as described above.