Figure 4.

Anti-Vi IgG induced by Vi vaccines is sufficient to impair infection. (A) Colony forming units (CFU) in the spleen of C57Bl/6 (WT) and IgM^s-/- mice immunized i.p with 2 µg Vi-PS, Vi-TT or PBS, then infected for 24 hours with 1x10⁵ CFU Vi+ S. Typhimurium TH177 14 days later. Data pooled from 2 experiments with n = 2 or 4 mice/group. (B) Serum anti-Vi IgG titres of WT and IgM^s-/- mice were assessed by ELISA. (C) Serum bactericidal activity of WT and IgM^s-/- sera was measured against TH177, represented as mean change from the starting LogCFU/mL bacterial dose, normalised to the negative control values at each timepoint. Error bars represent SEM. (D) Pooled WT hyperimmune anti-Vi sera were depleted of IgM using anti-mouse IgM coated Sepharose beads, and serum bactericidal activity against TH177 measured by SBA. Representative of individual serum samples, showing change from the starting LogCFU/mL bacterial dose, normalised to the negative control values at each timepoint. Complete human serum (CHS) was used as a positive control. (E) Spleen CFU counts of WT mice infected for 24 hours with 1x10⁵ CFU TH177 opsonised with IgM depleted serum. Data pooled from 2 experiments with n= 2 or 4 mice/group. *p<0.05, **p<0.01 and ns = non-significant by Mann-Whitney U test between individual groups (two-tailed).