Matrix metalloproteinase-7 facilitates immune access to the CNS in experimental autoimmune encephalomyelitis

Background: Metalloproteinase inhibitors can protect mice against experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis (MS). Matrix metalloproteinase-9 (MMP-9) has been implicated, but it is not clear if other MMPs are also involved, including matrilysin/MMP-7 - an enzyme capable of cleaving proteins that are essential for blood brain barrier integrity and immune suppression. Results: Here we report that MMP-7-deficient (mmp7(-/-)) mice on the C57BI/6 background are resistant to EAE induced by myelin oligodendrocyte glycoprotein (MOG). Brain sections from MOG-primed mmp7(-/-) mice did not show signs of immune cell infiltration of the CNS, but MOG-primed wild-type mice showed extensive vascular cuffing and mononuclear cell infiltration 15 days after vaccination. At the peak of EAE wild-type mice had MMP-7 immuno-reactive cells in vascular cuffs that also expressed the macrophage markers Iba-1 and Gr-1, as well as tomato lectin. MOG-specific proliferation of splenocytes, lymphocytes, CD4(+) and CD8(+) cells were reduced in cells isolated from MOG-primed mmp7(-/-) mice, compared with MOG-primed wild-type mice. However, the adoptive transfer of splenocytes and lymphocytes from MOG-primed mmp7-/- mice induced EAE in naive wild-type recipients, but not naive mmp7(-/-) recipients. Finally, we found that recombinant MMP-7 increased permeability between endothelial cells in an in vitro blood-brain barrier model. Conclusion: Our findings suggest that MMP-7 may facilitate immune cell access or re-stimulation in perivascular areas, which are critical events in EAE and multiple sclerosis, and provide a new therapeutic target to treat this disorder.