Distribution and functional plasticity of peripheral blood Th(c)17 and Th(c)1 in rheumatoid arthritis

With the discovery of Th17 cells, it became unclear whether rheumatoid arthritis (RA) is a Th1-mediated and/or a Th17-mediated disease. Objective: The aim of this study was to identify and characterize the pro-inflammatory function of IL-17-producing T cell subsets (Th(c)17) in RA. Flow cytometry analysis was performed on peripheral blood from RA patients with inactive or low disease activity (LDA, n = 19) and moderate to high disease activity (HDA, n = 13) to analyze the number and functional activity of Th(c)17 and Th(c)1 cell subsets according to the frequency of IL-2-, TNF-α- and IFN-γ-producers cells, as well as, their cytokine amount. Additionally, 13 age-matched healthy volunteers were added to the study. Our data point to a slight increase in Tc17 frequency in RA patients, more evident in HDA, and a higher ability of Th17 to produce IL-17, whereas a lower production of TNF-α was noted either in Th17 or Tc17 cells, particularly from HDA. A similar decrease was observed in Th(c)1 for almost all studied pro-inflammatory cytokines, with the exception of IL-2, which was increased in Tc1 from LDA patients. Analysing the proportion of pro-inflammatory cytokines-producing cells, a polarization to a Tc1 phenotype seemed to occur in CD8 T cells, while CD4 T cells appear to be decreased in their frequency of IFN-γ-producing cells. Taken together, the functional plasticity features of Th17 and Tc17 cells suggest a particular contribution to the local cytokine production, pointing an underestimated role, namely of Tc1 and Tc17 cells, in the RA pathophysiology.