Fig. 1

Protective associations and correlation between antibody-dependent fixation of C1q and complement-dependent invasion inhibition or GIA. a A longitudinal cohort of PNG children was used to calculate protective associations for functional antibodies as determined in Growth Inhibition Assays (GIA, complement-free conditions, n = 205, Mugil cohort) and C1q-fixation assays on the merozoite surface (n = 200). Children were stratified into three equal tertiles (based on ranks) and adjusted hazard ratios (aHR) were calculated using Cox proportional hazards model comparing high versus low (HvL) and medium versus low (MvL) responders. Black bars compare high versus low responders (HvL), grey bars compare medium versus low responders (MvL). b The correlation between C1q fixation on the merozoite surface and activity in antibody-complement invasion inhibition assays (IIA) among a subset of samples (n = 27) (data are shown as invasion (%) relative to controls). c The correlation between C1q fixation and activity in growth inhibition assays (GIAs) among the same subset of samples (n = 27) (data are shown as growth (%) relative to controls). d Shows the correlation between antibody-complement IIA and GIA among a subset of samples (n = 27). Spearman’s rho (r) and statistical significance (p) are indicated. Non-linear regression was used to generate a trendline. Dotted lines indicate 95% confidence intervals. e, f Study participants (n = 27) were stratified into three equal tertiles according to low, medium and high C1q fixation to the merozoite surface. The median invasion measured by antibody-complement IIA (e) and growth measured by GIA (f) was compared between the three groups (statistical significance determined by Kruskal–Wallis test)