CD4⁺ CD25⁺ regulatory T cells partially mediate the beneficial effects of FTY720, a sphingosine-1-phosphate analogue, during ischaemia/reperfusion-induced acute kidney injury

Background. The synthetic sphingosine-1-phosphate (S1P) analogue, FTY720, attenuates ischaemia/reperfusion (I/R) injury by inducing peripheral lymphopaenia. Recent studies suggest that FTY720 may also exert protective effects by modulating dendritic cell (DC) function or directly affecting regulatory T cells (Tregs). The purpose of the present study was to examine whether the beneficial effect of FTY720 in I/R-induced acute kidney injury (AKI) involves modulation of DCs or Tregs.Methods. Mice underwent bilateral ischaemia, and FTY720 or vehicle was then administered. Biochemical values, histological kidney damage and tissue inflammation were assessed. Phenotype and function of DCs in blood/spleen or kidney were also examined by flow cytometry or mixed lymphocyte reaction (MLR) assay. Percent Tregs or FoxP3 mRNA expression was examined in kidney and spleen, and depletion and adoptive transfer of Tregs were also performed.Results. Treatment with FTY720 attenuated I/R kidney injury and reduced inflammation. The beneficial effect of FTY720 was associated with expansion of peripheral CD11b⁺ CD11c⁺ DC and with maturation of spleen CD11c⁺ DC, which showed impaired allostimulatory capacity. FTY720-treated animals also showed a higher frequency of CD4 ⁺ CD25⁺ Tregs and an upregulation of FoxP3 mRNA expression in spleen and kidney. In vitro experiments showed that FTY720 induced expansion of Tregs, possibly via conversion from non-Tregs to Tregs. Depletion and adoptive transfer of Tregs were associated with loss and recovery of the beneficial effects of FTY720.Conclusion. These results suggest that the beneficial effects of FTY720 in I/R injury may be partially mediated by DC modulation or by increasing Treg activity. Further studies that identify tolerance induction mechanisms will be useful for developing strategies for the prevention or treatment of AKI.