Aim of the work: To measure interleukin-33 (IL-33) serum and synovial fluid (SF) levels as well as its relative
expression in peripheral blood mononuclear cells (PBMC) of juvenile idiopathic arthritis (JIA)
patients and to study their relation to clinical, laboratory and musculoskeletal ultrasound characteristics,
disease activity and functional status.
Patients and methods: The study included 60 JIA patients and 60 healthy controls and SF levels were measured
in 20. Juvenile arthritis disease activity score (JADAS27) and Juvenile Arthritis Multidimensional
Assessment Report (JAMAR) were assessed; Ten-joint grey scale (GS) and power Doppler (PD) MSUS score
was performed. Rheumatoid factor (RF) titer and C-reactive protein (CRP) levels were measured.
Results: In JIA patients, serum IL-33 levels (median 12.6; 7.4–23.8 ng/l) and its relative mRNA expression
(median 3.3; 2.5–3.7) were significantly higher than their levels in the controls (median 1.7; 0.8–2.4 ng/l
and median 1 ng/ml; p < 0.001). Polyarticular subtype (n = 20) had higher IL-33 serum levels compared to
oligoarticular (n = 28, p < 0.001) and systemic-onset (n = 12, p = 0.006) subtypes. In JIA patients, the
serum and SF levels of IL-33 significantly correlated with JADAS27 (p < 0.001 and 0.002 respectively),
CRP (p < 0.001 and 0.007 respectively), GS (p < 0.001 and 0.001 respectively) and PD (p < 0.001 and
0.005 respectively). Serum IL-33 correlated with RF (p = 0.039) while, SF IL-33 correlated with physical
function (p = 0.02).
Conclusions: JIA patients have significantly elevated IL-33 serum concentrations and mRNA expression
that considerably correlated with different inflammatory parameters, RF and physical function suggesting
that it could be a valuable marker of JIA disease activity and implies a possible prognostic role.

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This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-ncnd/
4.0/).