Fig. 3.

ZPS-conjugates confer protection against GBS challenge. (A) CD1 mice were immunized i.p. with ZPS and PS conjugates (1 μg). PS-conjugate plus alum was used as a positive and PBS as negative control. Two weeks after the third immunization, adult mice received a lethal challenge of GBS, and the percentage of survival 2 days after the injection was evaluated. Pooled data from two experiments are shown. (B) A lethal dose of GBS was administered s.c. to the offspring of mothers immunized as in (A). The challenge was performed within 48 h after birth, and the percentage of survival was estimated 2 days post-injection. Each experiment was repeated at least three times by using CD1 or Balb/C strains with similar outcome. Statistical significance was calculated with Fisher's Exact Test. *, P < 0.01. (C) Opsonophagocytosis assays were performed to evaluate the capacity of sera from mice immunized as in (A) to induce GBS killing by differentiated HL60 cells in presence of rabbit complement. Triplicate results from sera diluted 1:100 were expressed as the mean log₁₀ reduction in GBS colony-forming units before (T₀) and after (T₁) 60 min of incubation at 37 °C. From the whole titration curves of the same assay, we also calculated opsonophagocytosis titers that are indicated below the graph.