Immunoresponsive Gene 1: an important regulator of autoreactive CD4⁺ T Cells in mouse model of multiple sclerosis

Abstract Th17 and Th1 CD4 T cells play important roles in the pathophysiology of human MS and the mouse model of MS, experimental autoimmune encephalomyelitis (EAE). As per our findings, metabolic changes in MS alter the phenotypic and functionality of immune cells, which may influence their effector activities as disease progresses. IRG1 (Immuno response gene 1), encodes for cis-aconitic acid decarboxylase in TCA cycle & enhances the manufacture of mitochondria-selective metabolite, itaconic acid from cis-aconitate, is one such gene linking metabolism to immune effector function. It modulates inflammation in myeloid cells in addition to its antibacterial activity. The relevance of IRG1 in CNS autoimmunity, however, is still unknown. We used IRG1 KO mice to know what role it plays in EAE. We observed that global IRG1 KO showed significantly worsened clinical disease severity compared to their WT at the peak of the disease (3.3+0.50 vs. 2.1+0.50, p< 0.05). We found an evident early onset of disease induction & severity in the IRG1 KO as compared to the Wt (D9 vs. D13). Furthermore, to examine the mechanism of EAE pathogenesis, found a significantly higher infiltration of CD45 hicells (mainly Th17/Th1 cells) in the CNS of IRG1 KO mice compared to Wt mice. Adoptive transfer of CD45+ cells from immunized IRG1 KO augmented the disease progression in RAG1 deficient mice suggesting a possible role of IRG1 in a hyperactivated Th17 response. Also, itaconate treatment at the dose of 15mg/kg bw attenuated EAE disease relapse in SJL mice. Our findings suggest that IRG1/itaconate negatively regulates the Th17 immune response & moDCs’ function to attenuate the EAE disease progression, which may open a novel therapeutic avenue in the development of MS-related therapies.