Immune-mediated clearance of erythrocytes in autoimmune hemolytic anemia

In warm-reactive autoimmune hemolytic anemia, IgG autoantibodies are bound to erythrocytes but typically do not fix complement efficiently. IgG-coated cells enter the spleen and other parts of the RES, where they interact with Fc receptors on macrophages. Erythrocytes may be completely engulfed and destroyed by this interaction or may have only a portion of their membrane removed. In the latter case, the red cells will reshape into spherocytes, which are then destroyed on their next passage through the spleen. In cold-reactive disease, complement is typically fixed very efficiently and intravascular lysis by the complement cascade can occur. Alternatively, the presence of surface-bound complement (C3) can lead to extravascular red cell destruction by the spleen and other portions of the RES, such as the liver.