FIGURE 7.

Extracellular hemoglobin can be metabolized into hemoglobin dimer as well as heme. The hemoglobin dimer can bind to the haptoglobin and enter the cell mediated by CD163. Soon afterward, the hemoglobin dimer that enters the cell will be decomposed into heme. On the other hand, extracellular heme can bind to hemopexin and enter the cell mediated by CD91. In quick succession, heme and oxygen in the cell are catalyzed by heme oxygenased (HO1/2) to produce Fe²⁺ ions, CO and bilirubin. In addition, abnormal red blood cells can also be cleared by phagocytosis mediated by the expression of type II scavenger receptor (CD36) on the phagocytic membrane.