: Pathogenic Th17 cells play crucial roles in CNS autoimmune diseases such as multiple sclerosis (MS), but their regulation by endogenous mechanisms remains unknown. Through RNA-seq analysis of primary brain glial cells, we identified immuno-responsive gene 1 ( Irg1 ) as one of the highly upregulated gene under inflammatory conditions. Validation in the spinal cord of animals with experimental autoimmune encephalomyelitis (EAE), an MS model, confirmed elevated Irg1 levels in myeloid, CD4, and B cells in the EAE group raising the concern if Irg 1 is detrimental or protective. Irg1 knockout (KO) mice exhibited severe EAE disease, increased mononuclear cell infiltration, and increased levels of triple-positive CD4+ T cells expressing IL17a, GM-CSF, and IFNγ. A lack of Irg1 in macrophages elevates Class II expression, promoting the polarization of myelin-primed CD4+ T cells into pathogenic Th17 cells via the NLRP3/IL-1β axis. Adoptive transfer in Rag-1 KO and single-cell RNA sequencing highlighted the crucial role of Irg1 in shaping pathogenic Th17 cells. Moreover, bone marrow chimeras revealed that immune cells lacking Irg1 maintained pathogenic and inflammatory phenotypes, suggesting its protective role in autoimmune diseases, including MS. Immunoresponsive gene 1 ( Irg 1) was identified as a significantly elevated gene under inflammatory conditions through in vitro and in vivo models. Using global knockout mice, we identified Irg 1 as a protective endogenous gene that negatively regulates pathogenic Th17 cells. Single-cell RNA sequencing of infiltrating cells during EAE revealed that Irg 1 knockout enhanced the expression of pathogenic Th signatures in CD4+ T cells, indicating a robust proinflammatory environment. Irg 1 negatively regulates IL-1β in macrophages, which is essential for the differentiation of pTh17 CD4+ T cells, potentially clarifying the exacerbation of EAE in knockout animals. Our study identified Irg 1 as a negative regulator of both innate and adaptive immune responses in a CNS autoimmunity model.