Role of IL-12 receptor β1 in regulation of T cell response by APC in experimental autoimmune encephalomyelitis

IL-12 was thought to be involved in the development of experimental autoimmune encephalomyelitis (EAE), a Th1 cell-mediated autoimmune disorder of the CNS. However, we have recently found that IL-12 responsiveness, via IL-12Rbeta2, is not required in the induction of EAE. To determine the role of IL-12Rbeta1, a key subunit for the responsiveness to both IL-12 and IL-23, in the development of autoimmune diseases, we studied EAE in mice deficient in this subunit of IL-12R. IL-12Rbeta(1-/-) mice are completely resistant to myelin oligodendrocyte glycoprotein (MOG)-induced EAE, with an autoantigen-specific Th2 response. To study the mechanism underlying this Th2 bias, we cocultured purified CD4+ T cells and APCs of MOG-immunized mice. We demonstrate that IL-12Rbeta1(-/-) APCs drive CD4+ T cells of both wild-type and 1L-12Rbeta1(-/-) mice to an Ag-induced Th2 phenotype, whereas mild-type APCs drive these CD4+ T cells toward a Th1 type. IL-12Rbeta(-/-) CD4(+) T cells, in turn, appear to exert an immunoregulatory effect on the capacity of wild-type APCs to produce IFN-gamma and TNF-alpha. Furthermore, decreased levels of IL-12p40, p35, and IL-23p19 mRNA expression were found in IL-12Rbeta(-/-) APCs, indicating an autocrine pathway of IL-12/ IL-23 via IIL-12Rbeta1. IL-18 production and IL-18Ralpha expression are also significantly decreased in IL-12Rbeta(-/-) mice immunized with MOG. We conclude that in the absence of IL-12Rbeta1, APCs play a prominent regulatory role in the induction of autoantigen-specific Th2 cells.