CD4 and autoimmune disease: First, thymic Tregs (tTregs), also known as nTregs, are generated when CD4+ single-positive thymocytes encounter self-antigen stimuli in the thymus during development; T cell receptors (TCRs) expressed on tTregs mainly recognize self-antigens, which means tTregs have advantages in preventing autoimmune disease (26, 27).