Th17/Treg Imbalance in Sickle Cell Disease and Hydroxyurea Therapy

Tregs and proinflammatory Th17 cells have been described as two distinct subsets from Th1 and Th2 cells and have opposite effects in autoimmunity and inflammation. Th17/Treg balance controls inflammation and is important in the pathogenesis of autoimmune, infectious and chronic diseases. In view of growing evidence linking sickle cell disease (SS) and chronic inflammation and the potential anti-inflammatory role of Tregs cells, we hypothesized that SS is associated with decreased Treg subpopulation and consequent T cell dysfunction. Furthermore, the effects of hydroxyurea (HU) in this balance are not understood. To assess whether the Th17/Treg balance is impaired in patients with sickle cell disease, we investigated the peripheral blood Th17 and Treg frequencies and the expression of TGFβ1 and RORγT, a master regulator of Th17 differentiation, in sickle cell patients under HU therapy (SS-HU) and without HU (SSw/oHU). Methods. Thirty-eight patients with steady-state sickle cell disease (mean age 43 ± 10.5 yo; range 19–57 yo; 21 female/17 male), 19 SS-HU, 19 SSw/oHU and 20 healthy blood donors were evaluated. Tregs and Th17 quantification was performed by flow cytometry analysis and the expression of TGFβ1 and RORγT by q-PCR. Results. We found significant decrease in the Treg frequency (Foxp3+CD25+CD4+ population) comparing total SS patients and healthy controls (p=0.001) and this difference was more expressive between SS-HU and healthy controls (P=0.0006). Moreover, we found statistically increase of Th17 in SS-HU (p=0.02) and in SSw/oHU (p=0.01), comparing both with healthy controls. The TGFβ1 expression was increased in SS-HU (p=0.04) and SSw/oHU patients (p=0.01) when compared to control group. Interestingly, RORγT expression was significantly elevated only in SSw/oHU vs controls (p=0.03). Conclusion: Our results demonstrated a numerical imbalance of Th17/Treg in the peripheral blood of patients with SS disease. HU has no role mediating Th17/Treg plasticity and even SS patients under HU therapy remains Treg depleted. However, HU is able to modulated RORγT, corroborating the importance of other regulating factors during Th17 differentiation. Moreover, the higher expression of TGFβ1 may be an important positive instructive signal for Th17 differentiation. Th17/Treg imbalance might impact the disease presentation and phenotype and HU therapy may be involved in this issue.

No relevant conflicts of interest to declare.