HP (Haptoglobin) is a protein produced by hepatic cells that binds free plasma hemoglobin to make it accessible to degradative enzymes. It serves a protective function in the kidneys by preventing the loss of iron and protecting them from hemoglobin-induced damage. It has also been shown to have antimicrobial activity against bacteria. HP mutations and regulatory defects cause ahaptoglobinemia and hypohaptoglobinemia. Inherited HP polymorphisms are also associated with diabetic nephropathy, the incidence of coronary artery disease in type 1 diabetes, inflammatory disease behavior, Crohn's disease, primary sclerosing cholangitis, and susceptibility to idiopathic Parkinson's disease. In immunohistochemistry, HP has cytoplasmic and secretory positivity in the liver, and is also found in the kidneys, skin, lung and adipose tissue. References: The UniProt Consortium. Nucleic Acids Res. 47: D506-515 (2019); Nucleic Acids Res. 2016 Jan 4;44(D1):D733-45, PMID:26553804; J Crohns Colitis. 2008 Sep;2(3):214-8, PMID: 21172213,J Diabetes Complications. 2008 Nov-Dec;22(6):384-8, PMID: 18413152; Parkinsonism Relat Disord. 2015 Sep;21(9):1087-92, PMID: 26228081;