Abstract
We have identified a novel interleukin (IL)-7-responsive T cell population [forkhead box P3 (FoxP3(+) ) CD4(+) CD25(+) CD127(+) ] that is comparably functionally suppressive to conventional FoxP3(+) CD4(+) CD25(+) regulatory T cells (T(regs) ). Although IL-2 is the most critical cytokine for thymic development of FoxP3(+) T(regs) , in the periphery other cytokines can be compensatory. CD25(+) CD127(+) T cells treated with IL-7 phenotypically 'matured' into the known 'classical' FoxP3(+) CD4(+) CD25(high) CD127(-) FoxP3(+) T(regs) . In freshly isolated splenocytes, the highest level of FoxP3 expression was found in CD127(+) CD25(+) T cells when compared with CD127(-) CD25(+) or CD127(+) CD25(-) cells. IL-7 treatment of CD4(+) CD25(+) T cells induced an increase in the accumulation of FoxP3 in the nucleus in vitro. IL-7-mediated CD25 cell surface up-regulation was accompanied by a concurrent down-regulation of CD127 in vitro. IL-7 treatment of the CD127(+) CD25(+) FoxP3(+) cells also resulted in up-regulation of cytotoxic T lymphocyte antigen 4 without any changes in CD45RA at the cell surface. Collectively, these data support emerging evidence that FoxP3(+) T cells expressing CD127 are comparably functionally suppressive to CD25(+) CD127(-) FoxP3(+) T cells. This IL-7-sensitive regulation of FoxP3(+) T(reg) phenotype could underlie one peripheral non-IL-2-dependent compensatory mechanism of T(reg) survival and functional activity, particularly for adaptive T(regs) in the control of autoimmunity or suppression of activated effector T cells.