CD163, also known as M130, is a membrane glycoprotein which belongs to the scavenger receptor superfamily (PMID: 8370408). It is an acute phase-regulated and signal-inducing macrophage protein expressed exclusively in monocytes and tissue macrophages (PMID: 11196644). CD163 mediates endocytosis of haptoglobin-haemoglobin complexes (PMID: 11196644). The uptake of haptoglobin by macrophages contributes to the recycling of iron and also to the inflammatory response (PMID: 22900885). Soluble CD163 (sCD163), as a result of ectodomain shedding during inflammatory activation of macrophages, circulates in blood and has been suggested as a plasma/serum marker for macrophage activity (PMID: 12570164).