Serum and synovial fluid levels of interleukin-17 in correlation with disease activity in patients with RA

The aim of this study was to evaluate serum and synovial levels of IL-17A by ELISA in rheumatoid arthritis (RA) and find out the correlations between IL-17A levels and various clinical, laboratory parameters and RA disease activity and severity indices. Group I consists of 30 adult active RA patients fulfilling the ARA 1987 revised criteria, with knee effusion and receiving basic therapy, and with a mean age of 41.47 ± 11.49 years and mean disease duration of 9.5 ± 4.16 years. Group II consisted of 13 healthy volunteers, age- and sex-matched, with a mean age of 39.08 ± 14.19 years. RA patients showed significantly higher mean serum IL-17A levels than controls (11.25 ± 9.67 vs. 0.6 ± 1.4 pg/mL, respectively, p = 0.0002). Synovial IL-17A levels showed a significant positive correlation with serum IL-17A levels (r = 0.5 and p = 0.005). RA patients with negative rheumatoid factor (RF) had non-significantly higher mean serum IL-17A levels (12 ± 9.86 pg/mL) compared to those with positive RF (10.82 ± 9.81 pg/mL); however, the mean synovial IL-17A levels were nearly the same. Significant positive correlations were found between both serum and synovial IL-17A levels and DAS-28 scores (r = 0.556, 0.392 and p = 0.001, 0.032, respectively). RA patients with class III functional status showed significantly higher mean serum IL-17A levels (17.53 ± 13.43 pg/mL) than classes I and II (8.97 ± 6.97 pg/mL, p = 0.009). These led us to conclude that the elevated serum and synovial IL-17A levels in RA patients parallel the degree of disease activity and severity. This may highlight the usefulness of IL-17 (especially serum level) as a possible marker for more aggressive joint involvement and damage.