The most common antibody isotype involved in warm antibody AIHA is IgG, though sometimes IgA is found. The IgG antibodies attach to a red blood cell, leaving their FC portion exposed with maximal reactivity at 37 °C (versus cold antibody induced hemolytic anemia whose antibodies only bind red blood cells at low body temperatures, typically 28-31 °C). The FC region is recognized and grabbed onto by FC receptors found on monocytes and macrophages in the spleen. These cells will pick off portions of the red cell membrane, almost as if they are taking a bite. The loss of membrane causes the red blood cells to become spherocytes. Spherocytes are not as flexible as normal RBCs and will be singled-out for destruction in the red pulp of the spleen as well as other portions of the reticuloendothelial system. The red blood cells trapped in the spleen cause the spleen to enlarge, leading to the splenomegaly often seen in these patients.