Fig. 1.

Naturally acquired pre-challenge IE surface antibodies (αIE). a Dot plot showing the αIE levels in relation to prior exposure to P. falciparum (Mann-Whitney U test). The red bar indicates the median level. b-d shows IE surface staining of IgG from participant 110 (b), a hyperimmune Kilifi adult (c), pooled naïve European sera (d). The upper right quadrant shows the percentage of IE recognized by the antibodies. e-f αIE association with anti-MSP-2 (e) and anti-schizont extract (f). g Relationship between PMR and αIE, p value was calculated using Spearman’s correlation coefficient. MinExp = minimal prior exposure, DefExp = Definite prior exposure, Neg ctrl = negative control, post ctrl = positive control. αIE = antibodies to IE, OD = optical density, MSP-2 = merozoite surface protein 2, AB = sera from AB blood group, mdfi = median fluorescent intensity. αIE level for participant 110 is highlighted in blue