To investigate the levels of the T helper (Th)17-related cytokines interleukin 17A (IL-17A), IL-21, and IL-23 and their association with disease activity in rheumatoid arthritis (RA).
In a longitudinal sample set from patients with early RA (< 6 months; n = 40), we measured the plasma cytokine levels of IL-17A, IL-21, and IL-23 and analyzed for correlation with disease activity in 28 joints (Disease Activity Score 28-joint count; DAS28), C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and total Sharp score (TSS). In a transverse sample set of patients with chronic RA (> 8 years), using paired peripheral blood mononuclear cells and synovial fluid mononuclear cells, we investigated the cellular expression of IL-17A, IL-21, and IL-23R.
Patients with early-stage RA had significantly increased plasma levels of IL-21 and IL-23, but not IL-17A, compared to patients with chronic RA and healthy volunteer controls. Plasma levels of IL-21 and IL-23 after 12 months of treatment correlated with DAS28 and ESR, but not to TSS. Changes in IL-23 plasma levels from time of diagnosis to 12 months correlated with change in DAS28 and with TSS scores at 2 years. The numbers of CD4+ T cells producing IL-21 were significantly increased in the synovial fluid of patients with chronic RA, with only marginal coexpression of IL-21 and IL-17A.
Our results show a significant association between plasma levels of IL-21 and IL-23 and disease activity in RA, supporting the hypothesis that IL-21 and IL-23 are important pathogenic factors of this disease.