Therapeutic effect of low-dose IL-18 combined with IL-10 on collagen-induced arthritis by down-regulation of inflammatory and Th1 responses and induction of Th2 responses.

To investigate the anti-inflammatory or pleiotropic immunomodulatory role of interleukin-18 (IL-18), collagen-induced arthritis (CIA) mice were administrated with IL-18 along or in combination with IL-10, IL-4 or IL-12. IL-18 treatment along had no therapeutic effect on onset or established CIA mice. However, the combined treatment of low-dose IL-18 with IL-10 ameliorated the disease progression. Th1 cytokine expression was significantly inhibited, whereas Th2 cytokine expression was up-regulated in the synovial tissue by the IL-18/IL-10 treatment when compared with that in control group. Interestingly, IL-18 receptor (IL-18R) alpha expression was down-regulated by the treatment. According to the development of Th2 responses, GATA-3 mRNA expression was significantly increased in the treatment group. Our results indicated that combined treatment of low-dose IL-18 with IL-10 can prevent the development of CIA, which may be mediated not only by inhibiting Th1 responses through IL-18/IL-18Ralpha signaling, but also by inducing anti-inflammatory mediators through a GATA-3-dependent mechanism.