CD4 and autoimmune disease: In 1995, Sakaguchi (6) first identified a population of CD4+ cells expressing high levels of IL-2 α-chain receptor (CD25) in lymph nodes and spleens of BALB/c nu/+ mice, which could protect thymectomized mice from autoimmune disease and contribute to maintaining peripheral immune tolerance by suppressing immune responses against self- or non-self-antigens.