Levels of IL-15 in serum and cerebrospinal fluid of patients with Behcet's disease

Interleukin-15 (IL-15) is a novel proinflammatory cytokine, involved in the pathogenesis of inflammatory/autoimmune disease. The objective of our study was to measure serum and cerebrospinal fluid (CSF) IL-15 levels in patients with Behcet's disease (BD). CSF/serum IL-15 ratio was introduced to assess the origin of elevated IL-15 levels. We measured serum and CSF-IL-15 levels in 40 patients with BD (20 patients in active stage). Inflammatory and non-inflammatory neurological disease patients acted as controls. Active BD patients have significantly higher serum IL-15 levels (median 10.4 pg/ml; range 5.3-17.4) compared with BD in remission (6.05 pg/ml; 4-10.4) and healthy controls (4.65 pg/ml; 3.9-6.2). Similar serum IL-15 levels were found in active neuro-BD and inflammatory neurological disease (9.5 pg/ml; 5-13). Elevated levels of IL-15 were observed in CSF samples from neuro-BD patients (11 pg/ml; 8.5-15) and inflammatory neurological disease patients (10 pg/ml; 6.5-14) compared with patients with non-inflammatory neurological disease (4 pg/ml; 4-5.5; P < 0.001). Vascular cerebral BD lesions were associated with high CSF/serum IL-15 ratio. Our findings suggest that IL-15 is involved in BD inflammatory process, particularly in vasculitis foci, as an elevated CSF/serum IL-15 ratio characterizes vascular cerebral lesions.