CD163 is the high affinity scavenger receptor for the hemoglobin-haptoglobin complex and in the absence of haptoglobin - with lower affinity - for hemoglobin alone. It has also been shown to mark cells of monocyte/macrophage lineage. A soluble form of the receptor exists in plasma, commonly denoted sCD163. It is generated by ectodomain shedding of the membrane bound receptor. The existence of several CD163 isoforms, which differ in the structure of their cytoplasmic domains and putative phosphorylation sites, suggests that these isoforms also differ in their signaling mechanism.
