CD8A and autoimmune disease: - deficient positive selection at the CD4+CD8+ double-positive (DP) stage during T cell development in the thymus- reduction in SP thymocytes- development of autoimmune disease- reduced numbers of Foxp3+ regulatory T (Treg) cells- impaired suppressive function of Treg cells- impaired negative selection during T cell development in the thymus- deregulated Rag expression