A Ketogenic Diet Promotes Blood-Spinal Cord Barrier Resealing And Phenotypic Switching Of Pro-Inflammatory Myeloid Cell Infiltrates In A Preclinical Model Of Multiple Sclerosis.

We previously demonstrated that a ketogenic diet (KD) restored vision and motor functions to mice undergoing experimental autoimmune encephalomyelitis (EAE) when administered beginning the day of symptom onset. The follow up studies reported here demonstrate the impacts of the KD on immune cells and immune cell trafficking in this mouse model. The KD dramatically reduced the infiltration of all CD45HI immune cells into the spinal cords of EAE mice when fed for 2 weeks following symptom onset. This reduction was preceded by an increase of myeloid cells in the blood, primarily neutrophils and monocytes/macrophages. One mechanism underlying this altered distribution was accelerated resealing of the blood-SC barrier (BSCB), which initially opened at disease onset to different extents in EAE females and males but was rapidly resealed by the KD in both sexes. This resealing accompanied functional recovery and remarkably occurred whether KD feeding was initiated the day of symptom onset or 6-8 days after symptom onset. Consistent with this resealing, the KD reduced SC levels of secreted IL-1{beta}, the primary cytokine associated with compromising the integrity of CNS-blood barriers. As neutrophils mediate BSCB disruption and were the most markedly reduced infiltrating cell type in response to the KD, we found that the diet reduced SC levels of the neutrophil chemoattractant, CXCL2, and the neutrophil activator IL-6, as well as neutrophil markers of inflammation and pathogenicity. Non-linear dimensionality reduction analyses of our flow cytometry data further revealed that the KD induced phenotypic switching, reducing the frequency of pathogenic myeloid cells in the SC while increasing the frequency of myeloid cells expressing markers associated with resolving inflammation. These studies additionally revealed both common and distinct impacts of the KD on EAE female and male mouse immune cells. Collectively, this work advances a novel mechanistic understanding by which a KD ameliorates autoimmune-mediated MS-like pathologies to promote functional recovery and more broadly, implies that this dietary strategy has potential benefit for healing disrupted blood-CNS barriers and resolving inflammation in multiple neurodegenerative diseases.