Experimental autoimmune encephalomyelitis (EAE) serves as a model for multiple sclerosis and is considered a CD4+, Th1 cell-mediated autoimmune disease. IL-12 is a heterodimeric cytokine, composed of a p40 and a p35 subunit, which is thought to play an important role in the development of Th1 cells and can exacerbate EAE. We induced EAE with myelin oligodendrocyte glycoprotein (MOG) peptide 35–55 (MOG35–55) in C57BL/6 mice and found that while IL-12p40-deficient (−/−) mice are resistant to EAE, IL-12p35−/− mice are susceptible. Typical spinal cord mononuclear cell infiltration and demyelination were observed in wild-type and IL-12p35−/− mice, whereas IL-12p40−/− mice had normal spinal cords. A Th1-type response to MOG35–55 was observed in the draining lymph node and the spleen of wild-type mice. A weaker MOG35–55-specific Th1 response was observed in IL-12p35−/− mice, with lower production of IFN-γ. By contrast, a Th2-type response to MOG35–55 correlated with disease resistance in IL-12p40−/− mice. Production of TNF-α by microglia, CNS-infiltrating macrophages, and CD4+ T cells was detected in wild-type and IL-12p35−/−, but not in IL-12p40−/−, mice. In addition, NO production was higher in IL-12p35−/− and wild-type mice than in IL-12p40−/− mice. These data demonstrate a redundancy of the IL-12 system in the induction of EAE and suggest that p40-related heterodimers, such as the recently cloned IL-23 (p40p19), may play an important role in disease pathogenesis.

SIRT1 activators provide an important potential therapy to prevent the neuronal damage that leads to permanent neurologic disability in optic neuritis and MS patients. Intravitreal administration of SIRT1 activators does not suppress inflammation in this model, suggesting that their neuroprotective effects will be additive or synergistic with current immunomodulatory therapies.

Background Neuronal loss in multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE), correlates with permanent neurological dysfunction. Current MS therapies have limited ability to prevent neuronal damage. Methods We examined whether oral therapy with SRT501, a pharmaceutical-grade formulation of resveratrol, reduces neuronal loss during relapsing/remitting EAE. Resveratrol activates SIRT1, an NAD+-dependent deacetylase that promotes mitochondrial function. Results Oral SRT501 prevented neuronal loss during optic neuritis, an inflammatory optic nerve lesion in MS and EAE. SRT501 also suppressed neurological dysfunction during EAE remission, and spinal cords from SRT501-treated mice had significantly higher axonal density than vehicle-treated mice. Similar neuroprotection was mediated by SRT1720, another SIRT1-activating compound; and sirtinol, a SIRT1 inhibitor, attenuated SRT501 neuroprotective effects. SIRT1 activators did not prevent inflammation. Conclusions These studies demonstrate SRT501 attenuates neuronal damage and neurological dysfunction in EAE by a mechanism involving SIRT1 activation. SIRT1 activators are a potential oral therapy in MS.

Optic neuritis is an inflammatory disease of the optic nerve that often occurs in patients with multiple sclerosis and leads to permanent visual loss mediated by retinal ganglion cell (RGC) damage. Optic neuritis occurs with high frequency in relapsing-remitting experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis, with significant loss of RGCs. In the current study, mechanisms of RGC loss in this model were examined to determine whether inflammation-induced axonal injury mediates apoptotic death of RGCs. RGCs were retrogradely labeled by injection of fluorogold into superior colliculi of 6-7 week old female SJL/J mice. EAE was induced one week later by immunization with proteolipid protein peptide. Optic neuritis was detected by inflammatory cell infiltration on histological examination as early as 9 days after immunization, with peak incidence by day 12. Demyelination occurred 1-2 days after inflammation began. Loss of RGC axons was detected following demyelination, with significant axonal loss occurring by day 13 post-immunization. Axonal loss occurred prior to loss of RGC bodies at day 14. Apoptotic cells were also observed at day 14 in the ganglion cell layer of eyes with optic neuritis, but not control eyes. Together these results suggest that inflammatory cell infiltration mediates demyelination and leads to direct axonal injury in this model of experimental optic neuritis. RGCs die by an apoptotic mechanism triggered by axonal injury. Potential neuroprotective therapies to prevent permanent RGC loss from optic neuritis will likely need to be initiated prior to axonal injury to preserve neuronal function.

Multiple sclerosis (MS) and its animal model experimental autoimmune encephalomyelitis (EAE) are marked by inflammatory demyelinating lesions throughout the central nervous system, including optic nerve. Neuronal loss also occurs in MS and EAE lesions, but it is not known whether neuronal loss occurs secondary to inflammation, or as a primary process. In the current study, the relationship of inflammation to retinal ganglion cell (RGC) loss during acute optic neuritis is examined. RGCs were labelled with Flourogold, and EAE was induced in SJL/J mice by immunization with proteolipid protein peptide 139-151 (PLP). At various time points, RGCs were counted and optic nerves were examined for inflammatory cell infiltrates. No optic neuritis was detected prior to day 9 following immunization. Incidence of optic neuritis was 30% at day 9 and increased to over 70% by day 11, remaining high through day 18. In contrast, no RGC loss was detected in eyes with optic neuritis until day 14. A 43.1% reduction in RGC numbers at day 14 increased to 50.8% by day 18. No RGC loss occurred in eyes without optic neuritis. The fact that inflammation precedes RGC loss suggests that neuronal loss during optic neuritis occurs secondary to the inflammatory process.

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IL-12 was thought to be involved in the development of experimental autoimmune encephalomyelitis (EAE), a Th1 cell-mediated autoimmune disorder of the CNS. However, we have recently found that IL-12 responsiveness, via IL-12Rβ2, is not required in the induction of EAE. To determine the role of IL-12Rβ1, a key subunit for the responsiveness to both IL-12 and IL-23, in the development of autoimmune diseases, we studied EAE in mice deficient in this subunit of IL-12R. IL-12Rβ1−/− mice are completely resistant to myelin oligodendrocyte glycoprotein (MOG)-induced EAE, with an autoantigen-specific Th2 response. To study the mechanism underlying this Th2 bias, we cocultured purified CD4+ T cells and APCs of MOG-immunized mice. We demonstrate that IL-12Rβ1−/− APCs drive CD4+ T cells of both wild-type and IL-12Rβ1−/− mice to an Ag-induced Th2 phenotype, whereas wild-type APCs drive these CD4+ T cells toward a Th1 type. IL-12Rβ1−/− CD4+ T cells, in turn, appear to exert an immunoregulatory effect on the capacity of wild-type APCs to produce IFN-γ and TNF-α. Furthermore, decreased levels of IL-12p40, p35, and IL-23p19 mRNA expression were found in IL-12Rβ1−/− APCs, indicating an autocrine pathway of IL-12/IL-23 via IL-12Rβ1. IL-18 production and IL-18Rα expression are also significantly decreased in IL-12Rβ1−/− mice immunized with MOG. We conclude that in the absence of IL-12Rβ1, APCs play a prominent regulatory role in the induction of autoantigen-specific Th2 cells.

Experimental autoimmune encephalomyelitis (EAE), an inflammatory demyelinating disease of the CNS, is regarded as an experimental model for multiple sclerosis. The complement has been implicated in the pathogenesis of multiple sclerosis. To clarify the role of C in mouse EAE, we immunized mice deficient in C3 (C3−/−) and their wild-type (C3+/+) littermates with myelin oligodendrocyte glycoprotein peptide 35–55. C3−/− mice were susceptible to EAE as much as the C3+/+ mice were. No differences were found for the production of IL-2, IL-4, IL-12, TNF-α, and IFN-γ between C3+/+ and C3−/− mice. This finding shows that C3, a key component in C activation, is not essential in myelin oligodendrocyte glycoprotein peptide-induced EAE in mice.