Accumulation of FoxP3-expressing CD4+CD25+ T cells with distinct chemokine receptors in synovial fluid of patients with active rheumatoid arthritis

Objective: To explore the presence and characteristics of FoxP3-expressing CD4(+)CD25(+) regulatory T cells in synovial fluid (SF) of patients with active rheumatoid arthritis (RA). Methods: The frequency and chemokine receptors expression profile of FoxP3-expressing CD4(+)CD25(+) regulatory T cells in SF and peripheral blood (PB) from RA patients and PB from healthy controls were investigated by flow cytometry using three- or four-colour intracellular staining. Results: The frequency of CD4(+)CD25(+) FoxP3(+) T cells was increased significantly in SF compared with paired PB from RA patients and PB from healthy controls (p < 0.05). However, the frequency in PB from RA patients was significantly lower than in PB from healthy controls (p < 0.05). Notably, CD4(+)CD25(+)FoxP3(+) T cells in SF expressed increased levels of inflammation-related trafficking chemokine receptors, such as CCR4, CCR5, and CXCR4. Conclusion: There is an accumulation of FoxP3-expressing regulatory T cells in RA SF, and such recruitment may be dependent on the distinct chemokine receptors expressed on regulatory T cells.