Interleukin-34 in rheumatoid arthritis: potential role in clinical therapy

Objective: To investigate, whether interleukin (IL)-34 can be used as marker for treatment effectiveness in rheumatoid arthritis (RA). Methods: Serum samples were collected from 35 healthy participants and 83 patients with RA before as well as 4 weeks and 12 weeks after treatment initiation with the tumor necrosis factor alpha (TNF-alpha) inhibitor Etanercept. Related clinical data and hand radiograms of the patients were evaluated and serum IL-34, IL-6, IL-8, TNF-alpha, matrix metalloproteinase-3 (MMP-3) in addition to anti-cyclic citrullinated peptide (CCP) antibody concentrations were measured by ELISA. Results: Serum concentrations of IL-34, IL-6, IL-8, TNF-alpha, MMP-3 and anti-CCP antibodies were markedly elevated in RA patients compared with controls (P < 0.001), significantly decreased during treatment and correlated with erythrocyte sedimentation rate (ESR), C-reactive protein (CRP) and RA disease activity (P < 0.05). IL-34 correlated withIL-6, IL-8, TNF-alpha, MMP-3 and anti-CCP antibodies in RA patients at baseline (P < 0.01) and also with IL-8, MMP-3, IL-6, and DAS28 changes during therapy. Patients in stage III of hand X-ray RA scores had higher IL-34 serum concentrations than in stage II (P< 0.05). IL-34 level decreased significantly (P < 0.01) starting from 4 weeks after therapy initiation. Conclusions: IL-34 serum concentrations correlated with inflammatory cytokines before and during therapy and were significantly higher in stage III of hand X-ray score patients than in stage II participants. IL-34 might be used both as a biomarker for RA diagnosis and therapy efficiency.