CD6 is a protein found on the outer membrane of T-lymphocytes as well as some other immune cells. The encoded protein contains three scavenger receptor cysteine-rich (SRCR) domains and a binding site for an activated leukocyte cell adhesion molecule. CD6 is important for continuation of T cell activation, and mutations in the gene are associated with susceptibility to multiple sclerosis. CD6 has been found to be overexpressed in the inflamed mucosa of individuals with inflammatory bowel disease (IBD), where it is thought to increase intestinal immune responses. In immunohistochemistry of normal tissue, CD6 has positive staining in mature T cells, B1 cells, NK cells, CNS cells (basalganglia and cortex cerebellum), and mature medullary thymocytes. References: Nat Genet. 2009 Jul;41(7):776-82, PMID: 19525953, J Immunol. 2011 Sep 15;187(6):3286-91, PMID: 21849685; J Innate Immun 2011;3:420, PMID: 21178331; Journal of Neuroimmunology. 1990 Oct. 29(1–3):193-202, DOI: 10.1016/0165-5728(90)90162-G; Journal of Crohn's and Colitis. 2019 Apr. 13(4):510–524, DOI: 10.1093/ecco-jcc/jjy179