Homeostatic removal of senescent murine erythrocytes by splenic macrophages

Removal of senescent erythrocytes (RBC) from the circulation was investigated both in vivo and in vitro using inbred BALB/C mice as a model. Murine RBC were pulse-labeled in situ with 59Fe, and young and old peripheral blood RBC were separated by density gradient centrifugation on Percoll gradients. 59Fe labeled young RBC were found at a density of p 1.09. Forty days after 59Fe pulse labeling, 59Fe labeled RBC were found at p = 1.11 and 1.12, 59Fe labeled young or old cells were transfused into mice. Peripheral blood and spleen cell populations (i.e., macrophages, lymphocytes, polymorphonuclear leukocytes, and RBC) were assessed for radioactivity at varying time intervals after young or old RBC injection. Spleen cell populations were separated by density gradient centrifugation. The results revealed that senescent RBC were cleared more rapidly from the peripheral blood than were young RBC. and that the rate was related to the incorporation of senescent RBC by splenic macrophages. Studies performed in vitro revealed that splenic macrophages phagocytized autologous senescent RBC but not autologous young RBC. Thus, splenic macrophages can function as homeostatic regulators by selectively phagocytizing senescent cells in situ. Development of a murine model for RBC clearance studies should facilitate further studies on mechanisms of macrophage recognition of effete self RBC and other somatic cells.