Fig. 4.

Levels of AMA1-RON2 blocking antibodies correlate with protection. a The relationship between levels of AMA1-RON2 blocking antibodies (IC₅₀ Log10[EU]) and in vitro neutralization activity of the corresponding purified IgG. b The relationship between levels of AMA1-RON2 blocking antibodies (IC₅₀ Log10[EU]) in the plasma and time to infection after challenge in these animals. Spearman’s rank correlation coefficient (r_s) and P value are shown for each comparison. c Growth inhibitory antibodies largely target conformational epitopes in AMA1. The conformational and allele-specific dependency of antibodies to block invasion was assessed by measuring the ability of recombinant AMA1 to block the inhibitory activity of IgG. Saturating concentrations (2 µM) of recombinant FVO AMA1 (rFVO), reduced and alkylated FVO AMA1 (RArFVO) or 3D7 AMA1 (r3D7) were pre-incubated with IgG before assessing their GIA activity against FVO strain parasites. The amount of IgG from each animal was chosen such that they had 40–50% GIA before recombinant proteins were added and four or more animals each from Groups 2 and 3 were tested. ns, not significant