Serum interleukin-17 & nitric oxide levels in patients with primary Sjögren's syndrome

BACKGROUND & OBJECTIVES: The interleukin (IL)-17 producing T-helper cells have been linked to pathogenesis of autoimmunity and mostly investigated in rheumatoid arthritis (RA). In this study we tested the IL-17 levels, as well as the levels of nitric oxide (NO) as possible IL-17-induced product, in patients with primary Sjögren's syndrome (pSS), an intricate and complex chronic autoimmune disorder of exocrine glands. METHODS: Serum IL-17 levels and nitrite concentrations determined in patients with pSS (n=30) were compared with the values obtained in patients with RA (n=10) and healthy controls (n=15). The values obtained for IL-17 in pSS patients were also associated with the patients’ clinical characteristics, particularly the rheumatoid factor (RF) and total antinuclear antibodies (tANA) levels. RESULTS: Serum concentrations of IL-17 were significantly (P<0.01) higher in patients with pSS (12.9 ± 28.0 pg/ml) as compared to those obtained in healthy individuals (0.2 ± 0.6 pg/ml), but not as high as the values obtained for the patients with RA (34.5 ± 56.2 pg/ml). The mean IL-17 levels were significantly (P<0.05) higher in the pSS patients positive for rheumatoid factor (20.3 ± 33.3 pg/ml) than in RF-negatives (0.3 ± 0.6 pg/ml). Mean serum concentrations of IL-17 were also higher in antinuclear antibody (ANA)-positive samples (19.8 ± 33.5 pg/ml) in comparison to ANA-negative sera (1.1 ± 3.1 pg/ml) (P<0.05). The NO levels also showed elevated values in both pSS and RA patients, as compared to the healthy controls, since mean nitrite levels in patients with pSS and RA were 38.2 ± 29.2 μM and 41.7 ± 21.1 μM, respectively, while those in healthy controls were significantly lower, at 19.2 ± 10.5 μM. INTERPRETATION & CONCLUSIONS: The findings of this study showed that there was increased IL-17 and NO production in patients with primary SS, especially if they had associated elevated rheumatoid factor and antinuclear antibody values.