Initially identified in studies demonstrating a rapid in vivo clearance of CD47-deficient RBCs and an increased in vitro phagocytosis of normal RBCs by macrophages treated with SIRPα-blocking antibodies, the CD47/SIRPα system of cell clearance was suggested to play role in anemia of Rhnull individuals, given that expression of CD47 on normal RBCs is coupled to Rh antigen complex (Oldenborg et al., 2000). This evidence concerns the gene SIRPA and anemia (phenotype).