Objectives: Myeloid-derived suppressor cells (MDSCs) have recently been identified as an important mediator in inflammatory and autoimmune diseases through the production of arginase (Arg)-1 and inducible nitric oxide synthase (iNOS). The aim of this study was to investigate the prevalence of MDSCs in the peripheral blood of patients with rheumatoid arthritis (RA) and evaluate their correlation with T-helper (Th)17 cells.

Method: The frequency of MDSCs and Th17 cells and the mRNA expression of transcriptional factor RORγ-t and iNOS in the peripheral blood of RA patients and healthy controls (HC) were determined by flow cytometry and real-time reverse transcription polymerase chain reaction (RT-PCR), respectively. Plasma levels of interleukin (IL)-17, IL-6, tumour necrosis factor (TNF)-α, and Arg-1 were analysed by enzyme-linked immunosorbent assays (ELISA).

Results: Compared with HC, both the prevalence of circulating MDSCs and plasma Arg-1 increased significantly in RA patients. However, no significant difference was observed in the mRNA level of iNOS between RA patients and HC. The frequency of Th17 cells in RA patients was significantly higher than in HC but correlated negatively with the frequency of MDSCs and plasma Arg-1. A negative correlation between MDSCs and plasma TNF-α was also observed. However, the frequency of MDSCs was not correlated with plasma IL-6 and IL-17, nor with the mRNA level of RORγ-t.

Conclusions: We found a negative correlation between increased circulating MDSCs and Th17 cells in RA patients, which may provide new insights into the mechanisms involved in RA.