Expression of soluble programmed death-1 protein in peripheral blood regulatory T cells and its effects on rheumatoid arthritis progression.
1Department of Rheumatism, The First People’s Hospital of Jining, Jining, Shangdong 272000, P.R. China.2Department of Pharmaceutical, The First People’s Hospital of Jining, Jining, Shangdong 272000, P.R. China.3Department of Joint Surgery, The Affiliated Hospital of Jining Medical College, Jining, Shangdong 272000, P.R. China.
The present study aimed to investigate the role of the soluble programmed death‑1 (sPD-1) protein, which is released by peripheral blood regulatory T cells (Treg) during the progression of rheumatoid arthritis (RA). From October 2012 to May 2014, 82 RA patients (RA group) and 90 healthy volunteers (healthy controls; HC) were recruited. Cluster of differentiation (CD)4, CD25 and forkhead/winged helix transcription factor p3 (Foxp3) and expression of cytotoxic T lymphocyte associated antigen 4 (CTLA-4) and Foxp3 were detected by flow cytometry. Expression of sPD‑1 in Treg was detected by western blot analysis. Immunosuppressive activity of CD4+CD25‑ Treg was measured via thiazolyl blue in an MTT assay. ELISA was used to detect interleukin‑10 (IL‑10), transforming growth factor beta (TGF-β), interleukin-4 (IL-4), interferon‑γ (IFN-γ) and nuclear factor of activated T cells (NF‑AT). It was observed that in peripheral blood, CD4+CD25-FOXP3+/CD4+ levels were reduced in the RA group (P<0.001), and sPD‑1 levels were markedly higher (P<0.001), compared with the HC group. Additionally, it was observed that relative sPD‑1 protein expression in the small interfering RNA (siRNA)-sPD-1 treated group was reduced compared with the untreated and scrambled siRNA groups (all P<0.0001). The mean fluorescence intensity of CTLA-4 and Foxp3 decreased markedly upon transfection with siRNA-sPD-1 (P<0.001). Compared with the normal CD4+CD25‑ T group, optical density (OD)540 values, IFN-γ/IL-4 concentration ratio and NF‑AT activity in siRNA untreated and scramble groups reduced significantly (all P<0.001). OD540 value, IFN-γ/IL-4 concentration ratio and NF‑AT activity in the siRNA‑sPD‑1 group were significantly upregulated (all P<0.001). Therefore, sPD-1 may suppress the level of CD4+CD25‑ Tregs in the peripheral blood of RA patients, and may be involved in a variety of immune processes mediated by CD4+CD25‑ Tregs.