The distinct expressions of interleukin-15 and interleukin-15 receptor alpha in Behcet's disease.

Interleukin-15 (IL-15) is a pleotrophic cytokine that is involved in the pathogenesis of diverse inflammatory rheumatic diseases. The aims of this study were to compare serum IL-15 levels and expression of its receptor (IL-15Ralpha) in Behcet's disease (BD) with those in other rheumatic diseases and to identify the relationship between serum IL-15 levels and various clinical parameters in BD. One hundred fifty-eight subjects consisting of 40 BD, 38 systemic lupus erythematosus (SLE), 40 rheumatoid arthritis (RA), and 40 healthy controls were enrolled. Serum IL-15 levels were measured using an enzyme-linked immunosorbent assay. The proportion of IL-15Ralpha expression on each leukocyte subset was measured by flow cytometry. Erythrocyte sediment rate (ESR) and C-reactive protein (CRP) were measured for each enrolled subject. The clinical activity index of BD was assessed for BD patients. Serum IL-15 levels in BD patients are significantly higher than those of healthy controls, SLE, and RA patients (p < 0.001, p < 0.001, and p < 0.001, respectively). Serum IL-15 levels in BD were closely related to ESR (r = 0.405, p = 0.027), but not to CRP or the clinical activity index of BD (p > 0.05 for both). Additionally, there was no difference in serum IL-15 levels between active and inactive disease states in BD (p > 0.05). The proportion of IL-15Ralpha expression on total leukocytes was much lower for all rheumatic diseases, including BD, than in healthy controls (p < 0.01 for SLE, p < 0.01 for RA, and p < 0.05 for BD). IL-15 and IL-15Ralpha system may be involved in the inflammatory process and pathogenesis of BD.