Follicular helper T (Tfh) cells are specialized in helping B lymphocytes, which play a central role in autoimmune diseases that have a major B cell component, such as in rheumatoid arthritis (RA). Follicular regulatory T (Tfr) cells control the over-activation of Tfh and B cells in germinal centers. Dysregulation of Tfh cells and Tfr cells has been reported to be involved in the pathogenesis of some autoimmune diseases. However, the balance of Tfh and Tfr cells, and their roles in the development and progression of RA are still not clear.

In this study, we enrolled 44 patients with RA (20 patients with active RA and 24 patients with inactive RA) and 20 healthy controls, and analyzed the frequencies of circulating Tfh and Tfr cells, expression of programmed death-1 (PD-1), inducible co-stimulator (ICOS), intracellular IL-21, and pSTAT3 in Tfh cells, and serum levels of IL-6. The correlation among these parameters and that of Tfh or Tfr cells with disease activity were also analyzed.

Patients with RA (especially active RA) had higher frequencies of Tfh cells, but lower percentages of Tfr cells, thereby resulting in elevated ratios of Tfh/Tfr. Expression levels of PD-1 and IL-21 in Tfh cells were higher in patients with RA than in healthy subjects, while no difference in ICOS expression was observed between patients and controls. Both pSTAT3 expression and serum IL-6 levels increased in patients with RA, and positive correlation between them was observed. Additionally, pSTAT3 expression was positively correlated with Tfh cell frequency. The Disease Activity Score in 28 joints based on C-reactive protein (DAS28-CRP) was negatively correlated with Tfr cell frequency, but was positively correlated with both Tfh/Tfr ratio and PD-1 expression.

Results demonstrated that enhanced IL-6/pSTAT3 signaling may contribute to promotion of Tfh cells, consequently skewing the ratio of Tfh to Tfr cells, which may be crucial for disease progression in RA.