CTLA4 and Autoimmunity: While mice bearing heterozygous CTLA-4 mutations do not show an obvious phenotype, in humans these mutations result in either impaired interaction of CTLA-4 with its ligands (CD80 and CD86) or CTLA-4 haploinsufficiency, which are associated with a predisposition for autoimmune disorders and immune dysregulation syndrome [27,28].