FAS and autoimmune disease: Second, cytotoxic effector CD8+ T cells (CTL) can contribute to autoimmune disease by increased tissue infiltration, elevated release of lytic proteins or altered death receptor expression (Fas/CD95) leading to tissue damage.8 Besides identifying recently activated T cells, CD69 has been described to distinguish tissue-resident T cells from circulating T cells.16 Therefore, CD69 can also be used to study the possible retention of non-circulating CD8+ T cells in peripheral tissues and sites of inflammation.