Immune-responsive gene-1: The mitochondrial Key to Th17 Cell Pathogenicity in CNS Autoimmunity

AbstractPathogenic 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 elevatedIrg1levels in myeloid, CD4, and B cells in the EAE group raising the concern ifIrg1 is detrimental or protective.Irg1knockout (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 ofIrg1in 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 ofIrg1in shaping pathogenic Th17 cells. Moreover, bone marrow chimeras revealed that immune cells lackingIrg1maintained pathogenic and inflammatory phenotypes, suggesting its protective role in autoimmune diseases, including MS.SignificanceImmunoresponsive gene 1 (Irg1) was identified as a significantly elevated gene under inflammatory conditions through in vitro and in vivo models. Using global knockout mice, we identifiedIrg1 as a protective endogenous gene that negatively regulates pathogenic Th17 cells. Single-cell RNA sequencing of infiltrating cells during EAE revealed thatIrg1 knockout enhanced the expression of pathogenic Th signatures in CD4+ T cells, indicating a robust proinflammatory environment.Irg1 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 identifiedIrg1 as a negative regulator of both innate and adaptive immune responses in a CNS autoimmunity model.