Dimethyl fumarate protects from experimental autoimmune encephalomyelitis by modulating colonic immune cells

Dimethyl fumarate (DMF) is an oral therapy approved for the treatment of relapsing-remitting multiple sclerosis, and it is known to reduce disease severity in experimental autoimmune encephalomyelitis (EAE). Because self-reactive Th17 lymphocytes are thought to become activated in the gut before migrating to the central nervous system (CNS), we investigated how DMF modulates intestinal immune responses during EAE. Female C57BL/6J mice were immunized with MOG35-55 to induce EAE and treated with DMF (7.5 mg/kg, oral gavage, every 12 h) or vehicle starting at day 3 post-immunization (dpi). At the early chronic phase (d.p.i. 21), continuous DMF treatment reduced disease severity and CNS leukocyte infiltration. Notably, even short-term DMF administration (5 d) attenuated EAE compared to controls. To examine gut-specific effects, we profiled colonic gene expression after 5 d of treatment (dpi 8) using a NanoString autoimmune panel. We found that DMF downregulated genes associated with NF-κB and ERK1/2 signaling, pro-inflammatory cytokine production, and leukocyte migration in intestinal immune (myeloid) and epithelial cells. Flow cytometry analysis further demonstrated reduced interleukin (IL)-23a production by colonic macrophages and dendritic cells, thereby impairing pathogenic Th17 differentiation. Moreover, DMF decreased CXCR3, CCR6, and CXCR6 expression on MOG-reactive (V-β11+) Th17 cells, limiting their migratory potential to the CNS. Together, these findings show that DMF regulates Th17 differentiation and migration within the intestinal compartment, providing a mechanistic link to its protective effects in EAE.