Figure 5. Blood group O (H antigen) status affects the phagocytic uptake of infected erythrocytes by human macrophages.

Erythrocytes of blood group O and B were treated with B-zyme, thereby removing the terminal α-1,3-galactose from blood group B antigens. (A) Flow cytometric analysis with anti-B (clone 9621A8) and phycoerythrin (PE)-conjugated rat-anti-mouse kappa as secondary antibody. In the dot plot, the x and y axes represent FL1-derived fluorescence and PE-derived fluorescence, respectively, on logarithmic scales. Results show cleavage of the terminal galactose from B erythrocytes and enzymatic conversion from group B to erythrocytes which type as group O: (i) Native, untreated O erythrocytes, (ii) Native, untreated B erythrocytes, (iii) B-zyme-treated B erythrocytes. Group O cells mock-treated with B-zyme gave identical results to the group O untreated control (data not shown). (B) The phagocytic uptake was determined by counting the number of internalized infected erythrocytes in 250 individual macrophages and data was normalized to the average phagocytic index of infected untreated B erythrocytes. Data represent two independent experiments using the P. falciparum ITG clone. Each blood group is represented by four different donors. Bar graphs represent the mean±SEM. Significance was determined by Mann Whitney test with Bonferroni correction for multiple comparisons. There was an observed increase in the phagocytosis of untreated infected O erythrocytes when compared to untreated infected B erythrocytes (*p<0.05). The phagocytic index of the infected, B-zyme-treated B erythrocytes was significantly increased from phagocytic index of infected untreated B erythrocytes (**p<0.01). However, there was no significant difference in the uptake of treated vs. untreated infected O erythrocytes.