Using Experimental
Autoimmune Encephalomyelitis to Identify Prospective Treatments for Multiple Sclerosis
<p>Multiple sclerosis (MS) is an inflammatory disease, mediated by immune cells attacking the myelin sheaths that surround nerve axons. The autoimmune nature of this disease combined with heterogeneity in disease presentation and pathology makes MS a difficult disease to treat. Although some treatment options are currently available, there is strong demand for more effective treatment alternatives. Therefore, this thesis utilises an animal model of MS, experimental autoimmune encephalomyelitis (EAE), to identify new treatment strategies for MS. These studies encompass three separate lines of inquiry with the primarily focus on investigating the use and mechanisms of action by which microtubule-stabilising drugs (MSDs) modify EAE expression. Two other distinct and novel immunotherapies were also explored: the anti-psychotic drug, risperidone, and the Toll like receptor-9 and nucleotide oligomerization domain-containing protein 2 (TLR-9/NOD2) agonist, MIS416. MSDs are a class of anti-proliferative compounds, which can delay EAE disease onset and reduce disease burden. Administration of the MSD, paclitaxel, directly after EAE immunisation resulted in complete inhibition of antigen-specific encephalogenic responses within the spleen and attenuated responses within the lymph nodes. In contrast, administration of paclitaxel at a later time point did not alter antigen-specific responses, but inhibited immune cell infiltration into the central nervous system (CNS). Using in vivo proliferation and migration assays it was demonstrated that paclitaxel inhibited both immune cell proliferation and migration; indicating these two factors are likely to contribute to the disease modifying effects of MSDs. Futhermore, the combined administration of two MSDs, peloruside A and ixabepilone, resulted in synergistic disease suppression in vivo while the combination of paclitaxel and a currently used MS therapeutic, glatiramer acetate, also exhibited synergistic EAE suppression. Risperidone is an atypical antipsychotic used to treat schizophrenia, however there is evidence that risperidone can also modulate the immune system. The current study demonstrated that risperidone reduced EAE disease severity and induced an increase in splenic CD4⁺ T cells and antigen-specific IFN-γ production. Additionally, as macrophages have a crucial role in EAE disease development, the effect of risperidone on macrophage activation was explored. In cultured macrophages risperidone induced a reduction in IL-12 production and CD40 expression while increasing IL-10 production. These findings suggest that regulation of macrophage activation may contribute to the reduction in EAE. MIS416 is a novel microparticle that stimulates TLR9 and NOD2 receptors. A phase 2A trial is currently underway to evaluate the effects of MIS416 in progressive MS patients, yet the mechanisms by which MIS416 alters the immune system are not completely understood. The current study found that MIS416 effectively but transiently reduces EAE and that IFN-γ is necessary for this disease reduction. These experiments demonstrate that EAE is an appropriate model to further explore the precise mechanisms of action of MIS416. In summary, the work conducted in this thesis has identified the potential of three separate approaches to modify inflammatory disease processes in an animal model of MS. This research provides an initial foundation from which further research can be conducted, with the ultimate goal of developing new treatments for MS.</p>
