Increased expression of PD-1 on CD4+ T cells subsets in Rheumatoid Arthritis patients

Rheumatoid arthritis (RA) is a common chronic and systemic autoimmune disease, characterized by inflammation and the destruction of the joints. It is well known that CD4+ T cells play a major role in the pathogenesis of RA. Expanded subpopulations of CD4+ T cells have been reported in RA patients. Here, we investigated the expression of PD-1 on subsets of CD4+ T cells (CD4+CD28- and CD4+CD28+ T cells) in the peripheral blood (PB) and synovial fluid (SF) of patients with RA.

A total of 42 RA patients, including 10 newly diagnosed (ND) and 32 relapsed (RL) cases and also 20 healthy controls were enrolled. Phenotypic characterization subsets of CD4+ T cells were evaluated by flow cytometry, using fluorescence conjugated specific human monoclonal antibodies.

The frequency of CD4+CD28+ T cells was significantly increased in SF versus PB in ND and RL patients. In contrast, the percentage of CD4+CD28- T cells was elevated in PB of ND and RL patients comparison to SF. Expression of PD-1 on CD4+CD28+ and CD4+CD28- T cells in PB of ND and RL patients was significantly higher than the healthy controls. Furthermore, PD-1 expression on CD4+CD28+ and CD4+CD28- T cells in SF versus PB of RL patients were significant increased.

These data suggest that CD4+ T cells subsets in RA patients were resistance to PD-1 mediated effects and PD-1 has insufficient ability to suppression of CD4+T cells.