IL-18 directs autoreactive T cells and promotes autodestruction in the central nervous system via induction of IFN-gamma by NK cells.

IL-18 promotes NK cell and Th1 cell activity and may bridge innate and adaptive immune responses. Myelin oligodendrocyte glycoprotein (MOG) is a myelin component of the CNS and is a candidate autoantigen in multiple sclerosis. In the present study we show that IL-18-deficient (IL-18-/-) mice are defective in mounting autoreactive Th1 and autoantibody responses and are resistant to MOG35-55 peptide-induced autoimmune encephalomyelitis. IL-18 administration enhances the disease severity in wild-type mice and restores the ability to generate Th1 response in the IL-18-/- mice. This restoration was abrogated in NK cell-depleted mice, indicating that the action of IL-18 in promoting the generation of MOG-specific Th cells was dependent on NK cells. Furthermore, transfer of NK cells from recombinase-activating gene 1-/- mice, but not from recombinase-activating gene 1/IFN-gamma-/- mice, rescued the defective Th1 responses in IL-18-/- mice and rendered IL-18-/- mice susceptible to the induction of autoimmune encephalomyelitis. Thus, IL-18 can direct autoreactive T cells and promote autodestruction in the CNS at least in part via induction of IFN-gamma by NK cells.