The immunity-related GTPase Irgm1, also called LRG-47, is known to regulate host resistance to intracellular pathogens through multiple mechanisms that include controlling the survival of T lymphocytes. Here, we address whether Irgm1 also plays a role in the pathogenesis of experimental autoimmune encephalitis (EAE). We find that Irgm1/LRG-47 is a significant factor in the progression of EAE and multiple sclerosis (MS). Expression of Irgm1 was robustly elevated in MS-affected lesions and in the central nervous system (CNS) of myelin basic protein (MBP)-induced EAE mice, especially in cells of lymphoid and mononuclear phagocyte origin. Homozygous Irgm1 null mice were resistant to MBP-induced EAE, and CD4+ T cells in spleen and CNS of these mice displayed decreased proliferative capacity, increased apoptosis, and up-regulated interferon (IFN)-γ induction. Therefore, Irgm1-induced survival of autoreactive CD4+ T cells contributes significantly to the pathogenesis of EAE. Blockade of Irgm1 may be a potential therapeutic strategy for halting multiple sclerosis.—Xu, H., Wu, Z.-Y., Fang, F., Guo, L., Chen, D., Chen, JX, Stern, D., Taylor, GA, Jiang, H., Yan, SS Genetic deficiency of Irgm1 (LRG-47) suppresses induction of experimental autoimmune encephalomyelitis by promoting apoptosis of activated CD4+ T cells.