Figure 3. Murine monocytes phagocytose infected O erythrocytes more efficiently in vivo than infected A or B erythrocytes.

C57BL/6 mice were injected intraperitoneally with 50×10⁶ purified mature-stage P. falciparum parasites cultivated in human A, B or O erythrocytes. Three hours after injection, resident monocytes were collected, washed, and plated on glass coverslips. (A) The phagocytic index was calculated by counting the number of internalized parasites within 250 monocytes and the data were normalized to the average phagocytic index of infected A erythrocytes. Data represent three independent experiments using the P. falciparum strain ITG and each blood group is represented by at least 3 different donors, A (n = 5), B (n = 3) and O (n = 5). Bar graphs represent the mean±SEM. There was a significant increase in the phagocytic uptake of infected O erythrocytes compared to the phagocytic uptake of infected A or B erythrocytes (*p<0.05; Student's t-test with Bonferroni correction for multiple comparisons). (B) Photomicrographs show representative examples of increased uptake of mature-stage infected (i) O erythrocytes, versus mature-stage infected (ii) B erythrocytes. Images were acquired with an Olympus BX41 microscope and an Infinity capture camera at 1000× magnification.