Gene expression profiling reveals mast cell-dependent inflammation in the meninges in early EAE.

The meninges are generally considered relatively inert tissues that house the CSF and provide protection for the brain and spinal cord. However, our previous studies using Kit mutant (Kit W/Wv) mast cell-deficient mice demonstrated that mast cells residing in the dura mater and pia mater exacerbate the severity of experimental autoimmune encephalomyelitis (EAE), the rodent model of the CNS demyelinating disease, multiple sclerosis. These data suggest that the meninges are sites of active immune responses in disease. Gene expression profiles of meningeal tissue from wild type and mast cell deficient mice prior to and at day 6 post-EAE induction were found highly distinct. Increases in both mast cell- and neutrophil-associated transcripts were among the notable disease-related changes observed in wild type mice. Kinetic analyses show that meningeal mast cells are activated within 24 hours of disease induction to express multiple mediators including IL-1b and TNF as well as the neutrophil chemoattractant, CXCL2, an observation corresponding with an influx of neutrophils to the meninges. Neutrophil recruitment as well as the disease-related loss of BBB integrity is dependent on mast cell-derived TNF. These data provide unequivocal evidence that the meninges are sites of early inflammatory events in EAE. Mast cells residing within these tissues promote disease by orchestrating an early and efficient immune cell co-localization resulting in a robust local inflammatory response and a breach of the proximal BBB. We hypothesize that these events reflect an aberrant manifestation of the normal immune surveillance role of the meninges in infection settings.

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Christy AL, Walker ME, Hessner MJ, Brown MA