The aim of this study was to investigate the role of regulatory T cells (Tregs) in ankylosing spondylitis (AS).

We included 69 AS patients (15 of them received anti-tumor necrosis factor-apha agent-adalimumab) in the study and used a questionnaire to record the demographic data, disease activity index, functional index, human leukocyte antigen-B27, erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP). Thirty healthy subjects were used as controls. The peripheral blood mononuclear cells (PMBCs) were stained with anti-CD4, anti-CD25 and anti-Forkhead/winged helix transcription factor P3 (anti-FoxP3) antibodies and flow-cytometry was used to determine cell populations.

The percentages of Tregs in PMBCs were significantly higher in AS patients than in healthy controls. In AS patients who had poor disease functional index with higher levels of ESR and CRP were positively and significantly correlated with Tregs percentages in PMBCs. After adalimumab treatment in 15 patients, the percentages of Tregs, the ESR/CRP levels and the Bath Ankylosing Spondylitis Disease Activity Index/Bath Ankylosing Spondylitis Functional Index were significantly and gradually decreased over time.

The high expression of FoxP3 and CD25 on CD4⁺ T cells in PBMCs in AS patients was noted, and could be reversed by adalimumab therapy. These findings suggest that Tregs may play a role in modulating the inflammatory process in AS. Whether Tregs can be taken as a predictor for disease activity or treatment outcome is unclear and requires further study.