Serum level of interleukin-33 and soluble ST2 and their association with disease activity in patients with Behcet's disease.

Interleukin (IL)-33 is an important mediator of innate immunity. Behcet's disease (BD) is an autoinflammatory disorder characterized by hyperactivity of the innate immune response. We measured serum levels of IL-33 and its receptor soluble ST2 (sST2) in patients with BD to investigate their association with disease activity. Serum levels of both IL-33 and sST2 were higher in patients with BD compared with those in normal controls (IL-33: 594.48±175.04 pg/mL in BD and 224.23±56.64 pg/mL in normal controls [P=0.048], sST2: 99.01±15.92 pg/mL in BD and 23.56±3.25 pg/mL in normal controls [P<0.001]). IL-33 and sST2 expression in skin tissue, as shown by immunohistochemistry, was higher in patients with BD compared with that in the normal controls. Serum sST2 level correlated significantly with the BD currently active form (BDCAF), Iranian BD dynamic activity measure (IBDDAM), erythrocyte sedimentation rate and C-reactive protein. Multiple linear regression showed that serum sST2 was an independent factor associated with IBBDAM (regression coefficient, 0.374; P=0.004), and BDCAF (regression coefficient, 0.236; P=0.047). These results demonstrate that IL-33 and sST2 are highly expressed in patients with BD and that serum sST2 is an independent factor associated with IBDDAM and BDCAF, suggesting a potential role for sST2 as a surrogate marker of disease activity in patients with BD.