Figure 4. Increasing phagocytosis of erythrocytes correlates with decreasing A antigen.

A and O erythrocytes were typed using standard hemagglutinin techniques. Blood group A was further classified into A₁ or A₂ subgroups using Dolichos biflorus lectin. (A) Flow cytometric testing of A₁, A₂, O, and Bombay erythrocytes with anti-H (clone BRIC231) FITC conjugated antibody. FITC-derived fluorescence is displayed on the x axis on a logarithmic scale and the number of cells on the y axis. O (solid black line), A₂ (dotted black line), A₁ (dashed black line) and Bombay (filled grey). (B) A₁, A₂ and O erythrocytes infected with P. falciparum (ITG clone) were incubated with human monocyte-derived macrophages. The phagocytic index was calculated by determining the number of internalized parasitized erythrocytes within 250 macrophages. Data were normalized to the average phagocytic index of infected A₁ cells. Data represent 3 independent experiments and each blood group is represented by multiple donors, A₁ (n = 8/group), A₂ (n = 3/group), and O (n = 8/group). The box plots represent the median, interquartile and complete range. The phagocytosis of infected erythrocytes increased in an H antigen dose-dependent manner (r = 0.80, *p<0.0001; Spearman's correlation test).