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.