Elevated expression of PD‑1 on T cells correlates with disease activity in rheumatoid arthritis

It is well known that lymphocytes are important in rheumatoid arthritis (RA). Programmed cell death-1 (PD‑1) is one of the immunosuppressive costimulatory molecules, which mediates an inhibitory effect. However, its role in RA remains to be fully elucidated. In the present study, the expression levels of PD‑1 on T cells in the peripheral blood (PB) and synovial fluid (SF) were determined using flow cytometry. In addition, the expression levels of PD‑1 on T cells in the PB and SF of patients with RA were further analyzed to determine correlation with markers of the autoimmune response, inflammation and disease activity in RA. Compared with healthy controls, the expression of PD‑1 on T cells in the PB was significantly elevated in patients with RA (P<0.0001). The expression of PD‑1 on T cells in the SF of patients with RA was significantly increased, compared with that in the autologous PB (P<0.0001). It was also found that the expression of PD‑1 on T cells in the PB of patients with RA was increased significantly in subjects with a high rheumatoid factor titer, high levels of inflammatory markers and a high disease activity score 28 (DAS28). The expression of PD‑1 on T cells in the SF of patients with RA was increased significantly in subjects with a high DAS28. These data showed that the expression of PD‑1 on T cells was elevated in patients with RA and was correlated with the disease activity.