Although demyelination is a cardinal feature in multiple sclerosis, axonal injury also occurs. We tested whether a delay in axonal degeneration could affect the disease severity in two models for multiple sclerosis: experimental autoimmune encephalomyelitis (EAE) and Theiler's murine encephalomyelitis virus (TMEV) infection. We compared wild-type C57BL/6 (B6) mice with C57BL/Wld s (Wld) mice, which carry a mutation that delays axonal degeneration. In EAE, both mouse strains were sensitized with myelin oligodendrocyte glycoprotein (MOG) 35-55 peptide and showed a similar disease onset, MOG-specific lymphoproliferative responses, and inflammation during the acute stage of EAE. However, during the chronic stage, B6 mice continued to show paralysis with a greater extent of axonal damage, demyelination, and MOG-specific lymphoproliferative responses compared with Wld mice, which showed complete recovery. In TMEV infection, only Wld mice were paralyzed and had increased inflammation, virus antigen-positive cells, and TMEV-specific lymphoproliferative responses versus infected B6 mice. Because TMEV can use axons to disseminate in the brain, axonal degeneration in B6 mice might be a beneficial mechanism that limits the virus spread, whereas slow axonal degeneration in Wld mice could favor virus spread. Therefore, axonal degeneration plays contrasting roles (beneficial versus detrimental) depending on the initiator driving the disease.

The mechanism(s) responsible for generating the different forms of multiple sclerosis, primary progressive (PP) and secondary progressive (SP) versus relapsing-remitting (RR), is not well understood. Using myelin oligodendrocyte glycoprotein (MOG)(92-106), we have established animal models that mimic the different types of multiple sclerosis. A.SW mice develop PP or SP-experimental allergic encephalomyelitis (EAE) with large areas of demyelination and high titers of MOG antibody whereas SJL/J mice develop RR-EAE with perivascular T cells and mild demyelination. In A.SW progressive EAE, we found atrophy of the thymus, spleen, and lymph nodes with depletion of T and B cells and massive apoptosis, as demonstrated by immunohistochemistry, terminal dUTP nick-end labeling, and DNA agarose gel electrophoresis. To test whether lymphoid apoptosis itself contributes to disease progression, we injected SJL/J mice with apoptotic thymocytes. Injection of apoptotic cells resulted in greater than 20% of mice developing SP-EAE with ataxia. SJL/J mice with SP-EAE had large areas of demyelination, high MOG antibody titers and atrophic lymphoid organs. Spleen cells from mice with progressive EAE produced less interferon-gamma than those from RR-EAE when stimulated with mitogen. We suggest that induction of lymphoid apoptosis alters the balance of Th1 versus Th2 immune responses and increases MOG antibody production, leading to exacerbation of demyelination and subsequent disease progression.

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS). Adhesion molecules play important roles in cell-cell and cell-extracellular matrix (ECM) interactions in inflammation. Blocking the interaction between inflammatory cells and vascular endothelia can prevent cell entry into tissues and harmful inflammatory responses, that is, autoimmunity, but could also limit immunosurveillance by anti-viral T cells in sites of infection or latency. Development of progressive multifocal leukoencephalopathy in patients treated with antibody against very late antigen (VLA)-4 prompted us to explore an alternative therapeutic approach. We used an antibody against the integrin alpha2, VLA-2, that interacts with ECM, not vascular endothelium. SJL/J mice were sensitized with myelin proteolipid protein (PLP)(139-151) peptide to induce experimental autoimmune encephalomyelitis (EAE), an animal model for MS. Treatment of mice with VLA-2 antibody suppressed clinical signs and CNS inflammation of EAE, when antibody was given immediately after disease onset. In contrast, VLA-4 or VLA-2 antibody treatment of mice during the priming or remission phase of EAE had minor effects on the disease's clinical course. No differences were found in lymphoproliferative responses to PLP(139-151) among treatment groups. Data suggest that blocking cell-ECM interactions can be an alternative therapy for MS.