Percentages of CD4+CD161+ and CD4−CD8−CD161+ T Cells in the Synovial Fluid Are Correlated with Disease Activity in Rheumatoid Arthritis

OBJECTIVE: CD161 has been identified as a marker of human IL-17-producing T cells that are implicated in the pathogenesis of rheumatoid arthritis (RA). This study aimed to investigate the potential link between the percentage of CD161+ T cells and disease activity in RA patients. METHODS: Peripheral blood (PB) from 54 RA patients and 21 healthy controls was evaluated. Paired synovial fluid (SF) (n = 17) was analyzed. CD161 expression levels on CD4+, CD8+, and CD4-CD8- T cells were assessed by flow cytometry. RESULTS: The percentage of CD4+CD161+ T cells in RA SF was higher than RA PB, and it was positively correlated with DAS28, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP). CD4-CD8-CD161+ T cell percentage was decreased in RA PB and was further reduced in RA SF, and its level in SF was inversely correlated with DAS28, ESR, and CRP. However, CD8+CD161+ T cell percentage was neither changed in RA PB and SF nor correlated with disease activity indices. CONCLUSION: An increased CD4+CD161+ T cell percentage and a decreased CD4-CD8-CD161+ T cell percentage are present in RA SF and are associated with disease activity, and the accumulation of CD4+CD161+ T cells in SF may contribute to the local inflammation of RA.