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BACKGROUND: The normal red blood cell (RBC) life span may be significantly reduced when RBCs are stored under blood bank conditions, resulting in a reduced 24-hour survival after transfusion. The damage of stored RBCs is probably multifactorial as stored RBCs share features of both senescence and suicidal RBC death (eryptosis). Since an increased intracellular Ca2+ concentration ([Ca2+](i)) is one key feature of eryptosis, we here investigated if stored human RBCs had increased [Ca2+](i) and the mechanisms behind uptake of such RBCs in a murine model.

STUDY DESIGN AND METHODS: The intracellular Ca2+ content of RBCs was determined using the Ca2+ probe Fluo-3 and flow cytometry. In vivo uptake of Ca2+ ionophore-treated murine RBCs (Ca2+-RBCs) was investigated in recipient mice, using flow cytometry and immunohistochemical analysis.

RESULTS: A small fraction of human RBCs accumulated [Ca2+](i) during storage for up to 42 days under blood bank conditions. In a murine model, where fresh or Ca2+-RBCs were transfused, Ca2+-RBCs were mainly trapped by MARCO+ splenic marginal zone macrophages and CD11c+ CD207+ dendritic cells (DCs) within 1 hour after transfusion. In marked contrast, freshly transfused RBCs aging normally in circulation were cleared much slower and preferentially by F4/80+ red pulp macrophages. CD47 on the Ca2+-RBCs did not affect their clearance by splenic phagocytic cells.

CONCLUSIONS: A small fraction of RBCs accumulate [Ca2+](i) during storage, and in a murine model such RBCs are recognized by splenic macrophages and DCs in ways similar to what has been reported for nucleated apoptotic cells.