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Fig. 7 | BMC Medicine

Fig. 7

From: Human antibodies activate complement against Plasmodium falciparum sporozoites, and are associated with protection against malaria in children

Fig. 7

High levels of C1q-fixing antibodies to CSP are associated with protection against clinical malaria in children. PNG children (N = 206) were tested for C1q-fixation to CSP by ELISA. Results were standardized to arbitrary units (AU) based on malaria-naïve negative controls from Melbourne (seropositivity defined as AU > 1, shown as dotted lines). a C1q-fixation to CSP was categorized by age (≤8, 8.1–9, 9.1–10, and ≥10 for n = 47, n = 39, n = 38, and n = 71, respectively), and parasitemic status at enrolment by PCR. Each sample was tested in duplicate, and the mean value was used to generate box plots. The top, center, and bottom horizontal lines represent the 75th percentile, median, and 25th percentile, respectively. The upper and lower whiskers represent the highest and lowest values within the 1.5×-interquartile range, respectively. Values that exceed this range are presented as symbols. Reactivity between two groups and more than two groups was compared using the Mann–Whitney U test and Kruskal–Wallis test, respectively. b Kaplan–Meier survival curve showing the cumulative proportion of children who had experienced an episode of malaria during the follow-up (time in days), stratified into three groups based on C1q-fixation reactivity: negative (AU < 1), low positive (bottom 50% of positive samples, 1 < AU ≤ 1.525), and high positive (top 50% of positive samples, AU > 1.525), as shown in blue, red, and green, respectively (n = 116, n = 39, and n = 39, respectively; p = 0.0438, Wilcoxon Breslow test, unadjusted for confounders). AU arbitrary units, CSP circumsporozoite protein, ELISA enzyme-linked immunosorbent assay, PCR polymerase chain reaction, PNG Papua New Guinea

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