Comparative study of serum and synovial fluid interleukin-11 levels in patients with various arthritides

Objective: To determine the levels of serum and synovial fluid (SF) interleukin (IL)-11 in patients with various arthritides and estimate the contribution of IL-11 to acute phase response (APR). Design and methods: Serum and SF IL-11 were measured by ELISA in patients with rheumatoid arthritis (RA, n = 31), seronegative spondyloarthritis (SSA, n = 23), gout (GT, n = 14) and osteoarthritis (OA, n = 20) and were correlated with ESR and acute phase proteins as well as with cytokines IL-1α, IL-1β, IL-6, and TNFα. Results: IL-11 was detected in both serum and SF in each group, with IL-11 being statistically higher in SF than serum in all groups, suggesting reduced catabolism or increased synthesis of IL-11 intra-articularly. Median SF IL-11 levels were higher in OA patients than in other groups and in the treated than in the untreated RA subgroup. Moreover, serum and SF IL-11 were correlated significantly with each other, and moderately with the other cytokines examined in RA, SSA, and GT, but not in OA patients, while a significant negative correlation was found with a few of the inflammatory markers examined in each group. Conclusions: Our findings provide evidence of extensive intra-articular expression of IL-11 in arthritides, especially in OA and treated RA patients, suggesting a protective role for IL-11 in joints, probably through the induction of tissue inhibitor of metalloproteinases.