Fig. 4

Non-O blood groups reduce PfEMP1-DBL1α epitope accessibility. FCR3S1.2 (left column) and PAvarO (right column) parasites grown in erythrocytes from seven different donors from each blood group were exposed to anti-PfEMP1-DBL1ɑ antibodies for one hour. After treatment, rosetting rate (A, B) and rosette size (C, D) was evaluated by flow cytometry in BgO (squares), BgA (triangles), BgB (rhombus) and BgAB (circles) (mean ± SD). A, B Rosette disruption was measured as the absolute rosetting rate (percentage of multiplets). C, D Reduction of rosette size is shown as relative decrease of mean multiplets’ SSC-A. Samples were normalized to the mean SSC-A of the untreated samples for each blood group. E, F The accessibility of PfEMP1 in rosettes by antibodies was measured by immunofluorescence. Samples were normalized to the mean MFI of BgO. Pairwise comparison of BgO and all non-O Bgs performed using unpaired t-test with Holm adjustment of P-values indicated by asterisks (* P ≤ 0.05; ** P ≤ 0.01; *** P ≤ 0.001). All box plots display median values (middle line) and the lower and upper quartile values form the box, with whiskers extending to one and a half times the interquartile range