Interleukin-37 expression is decreased in Behçet's disease and is associated with inflammation.

Interleukin-37 (IL-37) exerts broad inhibitory properties on the innate inflammatory and acquired immune responses. This study was set up to investigate the expression of IL-37 in Behçet disease (BD) and to explore its possible regulatory role during inflammation. IL-37 protein levels and mRNA expression in lipopolysaccharides (LPS)-stimulated peripheral blood mononuclear cells (PBMCs) from 50 BD (30 patients in active stage) patients and 20 healthy controls were assayed by real-time polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA). Cytokines in the serum and the supernatants of stimulated PBMCs and CD4(+) T cells were assayed by ELISA. Active BD patients showed a decreased IL-37 expression and increased IL-1β, IL-6, and tumor necrosis factor-alpha (TNF-α) levels in serum and in PBMC culture supernatants. Active BD patients treated with corticosteroids showed an enhanced IL-37 production. Recombinant IL-37 (rIL-37) induced a significant decrease of inflammatory cytokines (IL-1β, IL-6, and TNF-α). It also markedly decreased IL-17 expression in PBMCs and CD4(+) T cells from active BD patients. The present study suggests that a decreased IL-37 expression in BD patients is associated with an increased inflammatory response. Corticosteroid treatment of active BD patients is associated with an increased expression of IL-37 mRNA, which suggests that treatment may partly exert its immunosuppressive effect by regulating IL-37 production and reducing inflammatory cytokines.