APCS (Serum Amyloid P Component / SAP) is a glycoprotein belonging to the pentraxin family of proteins. In the brain of patients with Alzheimer’s disease, APCS binds to amyloid fibrils and paired helical filaments and is present in cerebrospinal fluid, neurofibrillary tangles and amyloid plaques. It is used as a marker for amyloid deposits in immunohistochemistry. Roughly 14% of the dry mass of amyloid deposits is composed of APCS, and it is a likely contributor to the pathogenesis of amyloidosis. The binding of the encoded protein to proteins in the pathological amyloid cross-beta fold suggests its possible role as a chaperone. This protein is also thought to control the degradation of chromatin, and it has been demonstrated that APCS binds to apoptotic cells at an early stage. In immunohistochemistry of normal tissue, APCS is positive in plasma and in hepatocytes in the liver. References: Nature Medicine. 1997. 3 (8): 855–9, PMID: 9256275; PLoS One. 2016 Jul 18;11(7):e0159294, PMID: 27428539; Dementia. 1996 Sep-Oct;7(5):256-9, PMID: 8872416; PNAS May 5, 2009 106 (18) 7619-7623; PMID: 10.1073/pnas.0902640106; Cellular and Molecular Pathobiology of Cardiovascular Disease. Academic Press. 2014 Jan. 32. ISBN: 9780124052062;