Impaired regulatory T-cell homeostasis due to vitamin D deficiency in undifferentiated connective tissue disease

Objective: The aim of this study was to perform a quantitative and functional analysis of natural CD4+CD25(high)Foxp3+ regulatory T cells (nTregs) and CD4+IL-17+ T cells, and to assess the serum levels of proinflammatory cytokines in patients with undifferentiated connective tissue disease (UCTD) before and after 5 weeks of 0.5 mu g/day alfacalcidol supplementation. Methods: Twenty-five patients with UCTD were enrolled in an open-label trial of alfacalcidol. Plasma levels of 25-hydroxyvitamin D [25(OH)D] were assessed by a high-performance liquid chromatography (HPLC) method. Flow cytometry was used for the quantification of nTregs and the IL-17 expression of T-helper (Th)17 cells. The serum concentrations of cytokines interleukin (IL)-12, interferon (IFN)-gamma, IL-23, IL-17, IL-6, and IL-10 were measured by an enzyme-linked immunosorbent assay (ELISA). Results: Treatment with alfacalcidol raised 25(OH) D levels from a mean of 23.5 +/- 5.6 to 34.5 +/- 7.4 ng/mL (p = 0.059; NS). Alfacalcidol treatment decreased both Th1-(IL-12 and IFN-gamma) and Th17-related (IL-23, IL-17, IL-6) cytokine levels in UCTD patients, while the soluble IL-10 level increased (IL-12: 156.7 +/- 75.2 vs. 87.5 +/- 42.1 pg/mL, p < 0.001; IFN-gamma: 41.5 +/- 12.0 vs. 21.7 +/- 9.9 pg/mL, p < 0.001; IL-23: 385.2 +/- 82.2 vs. 210.0 +/- 69.3 pg/mL, p < 0.001; IL-17: 37.8 +/- 9.6 vs. 17.8 +/- 4.5 pg/mL, p = 0.009; IL-6: 39.4 +/- 11.3 vs. 23.5 +/- 6.3 pg/mL, p < 0.001, IL-10: 8.4 +/- 3.0 vs. 21.4 +/- 9.7 pg/mL, p < 0.001). Alfacalcidol improved the Th17/nTreg imbalance, as it inhibited the IL-17 expression of Th17 cells, and increased the number of nTregs. The alfacalcidol might increase the capacity of nTreg cells to suppress the proliferation of autologous CD4+CD25- cells. Conclusion: Our findings support the idea that vitamin D influences the Th17/nTreg imbalance in vitamin D-insufficient patients with UCTD and could be beneficial in the management of the disease.