Fig. 2: Evaluation of rabbit PrsA antisera in GAS surface binding, opsonophagocytic killing and passive protection in mice.

a Twenty-nine GAS strains of different emm-types were used to determine the bacterial surface targeting ability of PrsA-specific antibodies. The heat map values were calculated by subtracting the reads of PrsA-specific antibody group from the reads of the control IgG group and normalized to the values obtained from M1 A20 strain. Opsonophagocytic killing of GAS M1 A20 and its isogenic prsA1/A2 deficient mutant (b) and clinical GAS isolates with different emm-types (c) by human neutrophils in the presence of PrsA1 antisera, PrsA2 antisera or in combination compared to pre-immune sera. Data presented here were combined, normalized and expressed as means ± SD from two independent experiments, each performed in biological triplicates. d Human whole blood killing assay. M1 GAS (strain A20) was grown in human whole blood with the addition of rabbit control antibodies, purified rabbit anti-PrsA1 antibodies, anti-PrsA2 antibodies or in combination. Percent survival of GAS was calculated in comparison to the number of GAS surviving in the control antibody group. Each dot in the figure represents the corresponding value in each experiment. Data presented here were combined, normalized and expressed as means ± SD. e Kaplan–Meier survival curve of mice. Groups of female ICR mice (n = 15–25, pooled data from 2–3 independent experiments) were injected intraperitoneally with rabbit antisera raised against purified PrsA1 and PrsA2 or with pre-immune sera. Two hours later, the mice were challenged intraperitoneally with lethal dose of M1 GAS strain NTU24. A log rank test was used to compare the survival of PrsA antisera-treated animals with animal receiving pre-immune sera. One-way ANOVA with Tukey’s post hoc method was used for pairwise comparisons (b–d). * <0.05; ** <0.01; *** <0.005.