Fig. 1

Naturally acquired human anti-CSP antibodies are predominately IgG1, IgG3, and IgM, and can promote complement fixation to CSP. Antibodies from malaria-exposed adults (n = 30 in each group) living in PNG (a, c-e) and Kenyan (b) were tested for IgG/IgM and complement-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), and mean and range of duplicates were graphed (mean only for scatter plots). a,b IgG subclasses and IgM reactivity to CSP. The median, interquartile range, and percentage of positive samples are shown. c Correlations between C1q-fixation and C4/C3/C3/C5b-C9-fixation to CSP (Spearman’s correlation coefficient, rho). d Examples of C1q and C3-fixation to CSP by individual serum samples (V15, V32, V33, V45, and V46 from PNG donors, n = 5). e C3-fixation to CSP by individual samples (V6, V7, V32, V37, and V43 from PNG donors, n = 5) in the presence of normal human serum (NHS) and serum depleted of C1q (C1q dep.) (Wilcoxon matched-pairs signed rank test). Non-standardized data are shown, as only one Melbourne control (Melb.) was tested. AU arbitrary units, CSP circumsporozoite protein, dep. depleted, ELISA enzyme-linked immunosorbent assay, Melb. Melbourne, NHS normal human serum, PNG Papua New Guinea