Increased serum levels of interleukin-15 in rheumatoid arthritis with long- term disease.

OBJECTIVE: To study the serum levels of IL-15 in patients with rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), seronegative spondyloarthropathies (SSd) and healthy donors.
METHODS: The IL-15 serum levels were measured by ELISA in sera from 50 RA patients, 30 patients with SLE, 30 patients with SSd and 30 healthy donors. In RA patients, several clinical and demographic parameters were also obtained at the time of sample collection. IL-15 levels were compared in different RA subpopulations (positive or negative rheumatoid factor [RF], long term or recent onset disease, high or low disease activity). In addition, the possible association with other demographic and clinical parameters (gender, age, disease duration, etc) was also analysed.
RESULTS: RA patients had significantly higher serum levels of IL-15 (102.4 +/- 150 pg/ml; p = 0.0001) than SLE patients (9.8 +/- 15.3 pg/ml), SSd patients (7.9 +/- 14.6 pg/ml) and healthy donors' (5.2 +/- 11.6 pg/ml). RA patients with a disease evolution less than 2 years showed lower IL-15 levels (33.7 +/- 62.2 pg/ml) than those with long-term disease (152.4 +/- 64.6 pg/ml; p = 0.004). In addition, a significant correlation between IL15 in serum and the number of disease-modifying antirheumatic drugs (DMARDs) prescribed was detected in RA patients (r = 0.42; p = 0.002). No association between IL-15 levels and age, gender, RF or disease activity was observed in this group.
CONCLUSION: IL-15 is elevated in RA patients, specially in those with long term disease, compared to other rheumatic disorders. This finding supports that IL-15 is involved in the perpetuation of RA synovitis.