Regulatory T cell/Th17 balance in the pathogenesis of paediatric Behçet disease

Behçet disease (BD) is a chronic systemic inflammatory disorder of unknown aetiology. The aim of this study was to determine the orientation of T cell subpopulations in paediatric BD and more precisely to look for a regulatory T lymphocyte (Treg)/Th17 imbalance.

T cell subpopulations were analysed by flow cytometry in the peripheral blood of paediatric patients with acute BD (aBD; n = 24), remitting BD (rBD; n = 12) and in healthy controls (HCs; n = 24). Tregs (CD4+CD25hiCD127-/loFoxp3+), activated Tregs (GITR, LAP, CTLA-4 and HLA-DR expression), CD4+ and CD8+ T cells producing IFN-γ (Th1 and Tc1) or IL-17 (Th17 and Tc17) under polyclonal (OKT3/IL-2) or antigenic (Streptococcus sanguis KTH-1 peptides and heat shock protein 60) stimulation were enumerated.

Th17 (1.9- and 5.1-fold) and Tc17 (4.0- and 2.0-fold) frequency under mitogenic stimulation was significantly increased in aBD and rBD patients as compared with HCs. Th17 frequency under antigenic stimulation was also higher in patients than in HCs. The percentage and number of Tregs and activated Tregs in patients and in HCs were similar. However, when Tregs were removed, antigen-driven differentiation into Th1 and Th17 was significantly boosted in BD but not in HC CD4+ T cells.

There is a bias towards Th17 polarization in aBD and rBD in children. Although we did not observe an increase in the number of Tregs in these patients, their Tregs limit CD4+ T cell differentiation into Th1 and Th17 cells. Thus, in paediatric BD, Tregs seem to incompletely counterbalance a Th17 orientation of the Th cell response.