Interleukin-6 small interfering RNA improved the herpes simplex virus-induced systemic inflammation in vivo Behcet's disease-like mouse model

Abstract

It is known that the level of interleukin-6 (IL-6) is higher in patients with active Behcet's disease (BD) than in those with inactive disease. Herpes simplex virus (HSV) type 1 inoculation of the earlobes of ICR mice resulted in the development of BD-like symptoms. To find out whether downregulation of IL-6 would affect the symptoms of BD, IL-6 small interfering RNA (siRNA) was administered to a BD mouse model. IL-6 siRNA was intraperitoneally injected into BD mice to downregulate IL-6 (n=9). IL-6 siRNA injection downregulated serum IL-6 level (118.9±114.4 pg ml-1) compared with scramble injection (439.4±378.0 pg ml-1) in BD mice (P=0.01). In seven out of nine IL-6 siRNA-injected BD mice, 77.8% improved and the severity score was decreased from 3.1±1.05 to 1.7±0.87 (P=0.005), whereas two out of six (33.3%) scramble-injected BD mice improved and the severity score changed from 2.5±0.84 to 2.0±1.41 (P=0.203). Foxp3, RORγt, IL-17A, IL-17F and tumor necrosis factor-α were also influenced in IL-6 siRNA-injected BD mice compared with scramble-injected BD mice. Adoptive transfer of CD4+CD25+ cells to BD mice affected the decrease of IL-6 serum levels and were dependent on CD4+CD25+ cell numbers. These results showed that downregulation of IL-6 improved the inflammatory symptoms in BD mice through upregulation of regulatory T cells and inhibition of Th17 cells.