CD71 ⁺ Red Blood Cells Mediate Increased Erythrophagocytosis and Reduce Monocyte Number in a Monocyte Suspension Assay

Adverse reactions from donor‐recipient sex‐mismatched transfusions have been reported in the field of transfusion medicine. Immature CD71 + red blood cells (CD71 + RBCs) may influence these reactions through an immunomodulatory mechanism potentially linked to enriched intracellular reactive oxygen species (ROS). This study was conducted to investigate the effect of CD71 + RBCs on erythrophagocytosis, a common in vitro test for hemolysis risk in incompatible blood transfusions. Enriched CD71 + RBCs and CD71 − RBCs were exposed to allogenic peripheral blood mononuclear cells (PBMCs). CD71 + RBCs were also incubated with anti‐D sensitised CD71 − RBCs and PBMCs, in varying ratios, to assess any dose‐dependent behaviour. An ROS scavenger, apocynin, was applied to understand how CD71 + RBCs impact erythrophagocytosis. The phagocytosis index (RBC PI or CD71 + RBC PI) was measured using image flow cytometry. Supernatant haemoglobin was examined spectrophotometrically. The enriched CD71 + RBC group showed a significantly higher RBC PI and a reduction in the monocyte number compared to the CD71 − RBC group. Compared to the non‐treated group, the reduction of monocyte number and the increase of the phagocytosis index of CD71 + RBCs was partially reversed in the apocynin‐treated group. There were positive correlations between the dose of CD71 + RBC and CD71 + RBC PI and supernatant haemoglobin. Donated CD71 + RBCs enhance in vitro erythrophagocytosis of CD71 + RBCs in a dose‐dependent manner and reduce monocyte number. This work contributes to our understanding of immature CD71 + RBCs' role in post‐transfusion immunobiology.