CD59 (MAP-IP, MIRL, protectin) is a cell surface glycoprotein that regulates complement-mediated cell lysis and is involved in lymphocyte signal transduction. This protein is a potent inhibitor of the complement membrane attack complex, and it binds complement C8 and/or C9 during the assembly of this complex. This inhibits the incorporation of multiple copies of C9 into the complex, which is necessary for osmolytic pore formation. CD59 also plays a role in signal transduction pathways in the activation of T cells. Mutations in this gene cause CD59 deficiency, a disease resulting in hemolytic anemia, thrombosis, and cerebral infarction. In cancer, CD59 is positive in squamous cell carcinoma of the head and neck and in ovarian cancer, and sees upregulation in non-small cell lung cancer (NSCLC) and late stage colorectal cancer. In immunohistochemistry of normal tissues, CD59 has membranous and cytoplasmic positivity in tissues throughout the body. References: Journal of autoimmunity. 2014 53:67-77, PubMed:24698947; J Oral Pathol Med 2006;35:560, PMID: 16968237; Cent Eur J Immunol. 2015; 40(3): 349–353, PMID: 26648780; Arch Pathol Lab Med. 2014 Jul;138(7):910-9, PMID: 24978917; International Journal of Oncology. 2013. 43.3: 850-858, DOI: 10.3892/ijo.2013.2007