Altered Erythrocyte Function via TLR9-ox-mtDNA Binding Links Mitochondrial Oxidative Damage to Systemic Inflammation in Multiple Sclerosis.

Multiple sclerosis (MS), an autoimmune disorder of the central nervous system(CNS), is charactered by neuroinflammation and neurodegeneration. Red blood cells (RBCs) are the most abundant cells in circulation, yet their immunological roles remain poorly understood, especially in neuroimmunology. Here, we explored the role and mechanism of erythrocytes in linking CNS pathology to systemic inflammation in MS, by combining clinical epidemiology and experimental model validation. In UK Biobank (1,056 MS patients; 501,314 controls), MS patients exhibited significantly altered erythrocyte function. Notably, lower baseline erythrocyte counts were inversely associated with MS incidence. Our clinical cohort of 110 relapsing-remitting MS (RRMS) patients revealed progressive declines in RBC parameters (RBC counts, hemoglobin, hematocrit) which associated with disease duration and worse EDSS scores. In RRMS patients, RBCs proteomics and flow cytometry revealed TLR9 membrane translocation and CD47 downregulation. Ox-mtDNA-bound erythrocytes were more phagocytosed by macrophages, which subsequently triggered inflammatory activation and type I interferon responses. These findings were corroborated in the EAE model, where CNS-derived ox-mtDNA was found bound to erythrocyte TLR9, accompanied by compensatory erythropoiesis and interferon-β-driven inflammation. Treatment with the mitochondrial-targeted antioxidant MitoQ effectively normalized erythrocyte TLR9/CD47 expression, reduced ox-mtDNA release, and alleviated neuroinflammation. Collectively, our work defines a novel erythrocyte-TLR9-ox-mtDNA axis that links CNS mitochondrial damage to peripheral inflammation in MS. By integrating clinical cohort data with proteomics and experimental models, we establish erythrocyte pathology as a central feature of MS and highlight the therapeutic potential of targeting mitochondrial dysfunction to disrupt this cascade.