Objectives: Th17 cells are an effector T-cell population that plays a role in several chronic inflammatory conditions and are dependent on IL-23 for their survival and expansion. More recently, a genetic association was discovered between polymorphisms in the gene coding for the IL-23R and spondyloarthritis (SpA). Our aim was to evaluate the role of Th17 associated cytokines in SpA pathogenesis by measuring their levels in the joints and circulation of SpA patients as well as correlating them with disease activity parameters.
Methods: Paired synovial fluid (SF), serum and synovial biopsies were obtained from 30 non-PsA (non-psoriatic arthritis) SpA, 22 PsA and 22 rheumatoid arthritis (RA) patients. Interleukin-17, IL-23 and CCL20 were measured by ELISA in the SF and serum of the patients and correlated with systemic and local parameters of disease activity.
Results: SF IL-17 levels tended to be higher in non-PsA SpA compared to PsA and RA patients, whereas SF IL-23 levels were similar.
Concentrations of CCL20, a major Th17 attracting chemokine, tended to be higher in the joints of RA than in SpA patients. Interestingly, levels of CCL20 were markedly higher in synovial fluid as opposed to serum.
In addition, there was a remarkable association between the expression of the Th17 cytokine system and the presence of intimal lining layer hyperplasia in RA.
Also in the serum, there was a tendency for higher IL-23 levels in RA, which correlated strongly with disease activity parameters.
Conclusions: Th17 related cytokines are expressed in joints of SpA as well as RA patients. IL-23 levels, however, correlate with disease activity parameters in RA only. These results point towards a differential regulation of the Th17 cytokine system in SpA compared to RA.