CD163 (also called scavenger receptor cysteine-rich type 1 protein M130) is an acute-phase–regulated receptor that is involved in the clearance and endocytosis of hemoglobin/haptoglobin complexes by macrophages. It has a plasma membrane-bound form and a soluble form. CD163 is expressed on monocytes and mature resident macrophages such as red pulp macrophages in the spleen, Kupffer cells in the liver, alveolar and interstitial macrophages in the lung, medullary and perifollicular macrophages in lymph nodes, and perivascular and meningeal macrophages in the brain. The soluble form may be a biomarker for inflammatory diseases. Antibodies to CD163 can be used to identify monocytes and macrophages. It is positive in histiocytic sarcomas. References: Diagn Pathol. 2007;2:7. doi: 10.1186/1746-1596-2-7;Biochem Biophys Res Commun. 1999;260(2):466-474. doi: 10.1006/bbrc.1999.0866;J Leukoc Biol. 1999;66(5):858-866. PMID: 10577520;Nature. 2001;409(6817):198-201. doi: 10.1038/35051594;J Leukoc Biol. 2006;79(4):837-845. doi: 10.1189/jlb.1005602;Antioxid Redox Signal. 2013;18(17):2352-2363. doi: 10.1089/ars.2012.4834.