Infected O erythrocytes are phagocytosed more avidly by human macrophages.

<p><i>P. falciparum</i> (ITG and 3D7)-infected and uninfected A, B and O erythrocytes were incubated with A and O blood group macrophages for 90 minutes (ring-stage) or for 120 minutes (mature-stage). The phagocytic index was then calculated by determining the number of internalized parasites in ≥250 macrophages and the data were normalized to the average phagocytic index of infected A erythrocytes. (A) Data for ring-stage parasitized erythrocytes are presented as the combined results of two independent experiments. Data for each blood group (n = 3 donors/group) are shown as box-and-whiskers plot, representing interquartile and complete ranges, with the horizontal line in each box indicating the median. There was a significant increase in the phagocytic uptake of ring-stage infected O erythrocytes compared to A and B infected erythrocytes (*p = 0.022, and **p = 0.007, respectively; Student's <i>t</i>-test for paired samples with Bonferroni correction for multiple comparisons). (B) Data for mature-stage parasitized erythrocytes represent the combined results of six independent experiments using multiple donors per group (A: n = 6; B: n = 3; O: n = 4) and are shown as box-and-whiskers plots, representing interquartile and complete ranges, with the horizontal line in each box indicating the median. There was significantly enhanced phagocytic uptake of infected O erythrocytes observed compared to A and B infected erythrocytes (*p<0.01 and **p<0.05, respectively; Student's <i>t</i>-test with Bonferroni correction for multiple comparisons). (C) Macrophages were isolated from donors of blood groups A and O and phagocytosis assays were run in parallel. The blood group of the infected erythrocytes was found to influence phagocytic uptake, with infected O erythrocytes being preferentially phagocytosed (*p<0.01, two-way ANOVA), whereas the blood group of the macrophage had no effect on the uptake of infected A and O erythrocytes (p>0.05). Data represent three independent experiments normalized to the average phagocytic uptake of infected A erythrocytes by macrophages isolated from blood group A donors.