Higher levels of intracellular Foxp3 and CTLA-4 and lower levels of surface CD127 consistently distinguish CD25 hi cells from CD25 int/low and CD25 − cells ( 11). The expression of intracellular CTLA-4 and Foxp3 is positively correlated with surface CD25 expression ( 10). T reg cells are often defined as CD3 +CD4 +CD25 +Foxp3 + cells ( 5- 9). While no single marker uniquely identifies T reg cell populations, panels of markers allow identification of CD4 + T cells with suppressive activity. Natural T reg cells constitutively express CD25 (IL-2-receptor α-chain) ( 5), cytotoxic T lymphocyte-associated antigen 4 (CTLA-4 or CD152) ( 6), and the forkhead/winged helix transcription factor Foxp3, which is a key control gene in their development and function ( 7). Multiple T reg cell populations have been reported ( 3), with natural T reg cells the best characterized ( 4).
CD4 + regulatory T cells (T reg cells) suppress effector T cells and prevent or limit reactivity to self-antigens ( 1) and pathogens ( 2), blunt inflammation, and maintain antigen-specific T cell homeostasis ( 3).
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