Figure 4

Plasmodium falciparum strains show a preference for invading O+ erythrocytes over A+ erythrocytes. The preference of four P. falciparum strains for one or more of the ABO blood groups was assessed using an erythrocyte preference assay. Blood group A+, B+, O+ and AB+ erythrocytes were labelled with 1 or 10 µM of DDAO, 10 µM of OG, or a combination of both and mixed so that each well contained erythrocytes from all four blood groups. The erythrocyte mixtures were co-incubated with P. falciparum strain Dd2, 7G8, HB3 or GB4 parasites for 48 h to allow rupture of schizonts and subsequent invasion of labelled erythrocytes. Parasitemia was determined by flow cytometry after staining with Hoechst 33342, and the proportion of invaded erythrocytes was calculated as a percentage of total invaded labelled erythrocytes in each well. 40 different healthy volunteers, 10 for each blood group, were used, and each individual blood sample was tested in 3 different combinations of A+, B+, O+ and AB+, with 30 total combinations tested. Statistical significance was determined using one-way ANOVA with Tukey’s multiple comparison test (*p < 0.05).