Expression of programmed death-1 (PD-1) on CD4+ and CD8+ T cells in rheumatoid arthritis

Rheumatoid arthritis (RA) is characterized by chronic inflammatory process that targets the synovial lining of diarthrodial joints. Programmed death 1 (PD-1) plays a key role in the negative regulation of the immune response. In the current study, we investigated the expression of PD-1 on peripheral CD4+ and CD8+ T cells in RA patients. Percentage of PD-1+ cells was measured by flow cytometry in 82 RA cases and 90 healthy controls. Results showed that PD-1 expression was significantly decreased in both peripheral CD4+ and CD8+ T cells in RA (p = 0.002 and p < 0.001, respectively). Similarly, serum levels of soluble PD-1 were also downregulated in RA cases. When comparing PD-1 level in RA patients with different clinical parameters, patients with positive C-reactive protein (CRP) revealed lower proportion of PD-1 on CD4+ and CD8+ T cells than those with negative CRP. Also, disease activity score of RA patients was inversely correlated with PD-1 expression on peripheral CD4+ and CD8+ T cells. These data suggested that PD-1 may act as a negative regulator in the pathogenesis and progression of RA.