Red blood cells with elevated cytoplasmic Ca(2+) are primarily taken up by splenic marginal zone macrophages and CD207+ dendritic cells.

Abstract

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 Ca(2+) concentration ([Ca(2+) ]i ) is one key feature of eryptosis, we here investigated if stored human RBCs had increased [Ca(2+) ]i and the mechanisms behind uptake of such RBCs in a murine model. The intracellular Ca(2+) content of RBCs was determined using the Ca(2+) probe Fluo-3 and flow cytometry. In vivo uptake of Ca(2+) ionophore-treated murine RBCs (Ca(2+) -RBCs) was investigated in recipient mice, using flow cytometry and immunohistochemical analysis. A small fraction of human RBCs accumulated [Ca(2+) ]i during storage for up to 42 days under blood bank conditions. In a murine model, where fresh or Ca(2+) -RBCs were transfused, Ca(2+) -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 Ca(2+) -RBCs did not affect their clearance by splenic phagocytic cells. A small fraction of RBCs accumulate [Ca(2+) ]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.