End-stage renal failure and regulatory activities of CD4+CD25bright+FoxP3+ T-cells

Background. The defensive immune system in patients with end-stage renal failure is impaired at multiple levels. This state of immune incompetence is associated with continuous activation of the immune system. An additional explanation for this state of activation may be the disturbed function of CD4(+)CD25(bright+)FoxP3(+) regulatory T-cells. Methods. The phenotype and function of peripheral regulatory T-cells from patients with end-stage renal failure (N = 80) and healthy controls (N = 17) was studied by flow cytometry, RT-PCR and mixed lymphocyte reaction. Patients were on haemodialysis (N = 40), peritoneal dialysis (N = 26) or not treated with dialysis yet (N = 14). The latter group had a glomerular filtration rate of < 20 ml/min/ 1.73 m(2). Results. The basal IL-2 mRNA level was high in patient-PBMC (P = 0.0002 versus healthy controls). The absolute number of CD4(+)CD25(bright+) T-cells was low in patients (P < 0.05 versus healthy controls). Furthermore, proliferation of patient-PBMC upon allogeneic stimulation was impaired (P < 0.0001 versus healthy controls). The regulatory function of CD4(+)CD25(bright+) T-cells was determined in the setting of direct allorecognition. First, the effect of depletion of CD25(bright+) cells from patient-PBMC on proliferation was low. Second, co-culture of CD25(bright+) cells with CD25(neg/dim) cells (1:10 ratio) showed impaired regulatory function (P < 0.001 versus healthy controls), which was especially pronounced in patients on dialysis. The FOXP3 mRNA level was also low upon stimulation (P = 0.0002 versus healthy controls). Conclusions. In line with previous studies, we observed an overactivated but functionally compromised immune system in patients with end-stage renal failure. It now appears that in this setting, regulation by CD4(+)CD25(bright+)FoxP3(+) T-cells is also impaired.