Figure 16-1 MECHANISM OF EXTRAVASCULAR HEMOLYSIS IN AUTOIMMUNE HEMOLYTIC ANEMIA.

A, Macrophage encounters an IgG-coated erythrocyte and binds to it via its Fc receptors. Thus entrapped, the red blood cell (RBC) loses bits of its membrane as a result of digestion by the macrophage’s ectoenzymes. The discoid erythrocyte transforms into a sphere. B, RBC lightly coated with IgG (and therefore incapable of activating the complement cascade) is preferentially removed in the sluggish circulation of the spleen. C, RBC with a heavy coat of IgG; thus, C3b (black circles) can be removed both by the spleen and the liver.

(From Cunnigham MJ, Silberstein LE: Autoimmune Hemolytic Anemia. In Hoffman R, Benz EJ Jr, Shattil SJ, et al, eds: Hematology: Basic principles and practice, ed 4, 2005, Philadelphia, Elsevier.)

Table 16-1 Properties and Specificities of Red Blood Cell Autoantibodies

CAIHA, Cold autoimmune hemolytic anemia; Ig, immunoglobulin; WAIHA, warm autoimmune hemolytic anemia.