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autologous blood and marrow transplantation - Blog Science ...

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EAE.<br />

Burt et al.<br />

465<br />

Because lymphocytes from a normal mouse do not respond (proliferate<br />

or release cytokines) when presented with PLP or MBP epitopes, we assumed that<br />

myeloablation with total-body irradiation <strong>and</strong> rescue with nondiseased syngeneic<br />

<strong>marrow</strong> would result in a return to myelin-specific immune unresponsiveness.<br />

However, despite clinical <strong>and</strong> histologic improvement, there was no improvement<br />

in proliferative responses. Improvement correlated with myelin-specific delayed<br />

type hypersensitivity but not proinflammatory cytokine profile or proliferative<br />

responses. 16<br />

This indicates either a posttransplant dissociation between lymphocyte<br />

proliferative <strong>and</strong> cytotoxic effector pathways or presence of a posttransplant<br />

regulatory or suppressor subset of lymphocytes. HSCT of R-EAE appears to result<br />

in a posttransplant "pro-tolerance environment." The mechanisms <strong>and</strong> milieu of a<br />

posttransplant tolerogenic environment are unclear. We are currently studying this<br />

effect by retroviral mediated gene marking studies.<br />

THEILER'S MURINE ENCEPHALOMYELITIS VIRUS (TMEV)<br />

TMEV is an enteric murine picornavirus that causes a CNS biphasic disease<br />

marked by an initial viral cytopathic infection followed by autoimmune-mediated<br />

demyelination. The disease has a chronic primary-progressive course similar to<br />

primary-progressive multiple sclerosis. The importance of the immune system in<br />

clearing virus <strong>and</strong> controlling the initial cytopathic effect is supported by clearance<br />

of TMEV from the CNS of disease-resistant murine strains, persistence of CNS<br />

infection in disease-susceptible strains, <strong>and</strong> abrogation of resistance by use of<br />

immunosuppressive total-body irradiation. 25<br />

" 27<br />

The importance of the immune<br />

system in mediating progressive demyelination is supported by correlation of<br />

demyelination with both virus-specific <strong>and</strong> myelin peptide-specific delayed type<br />

hypersensitivity reactions <strong>and</strong> prevention of demyelination in disease-susceptible<br />

strains of mice after treatment with immunosuppressive agents such as cyclophosphamide,<br />

antithymocyte globulin, or irradiation. 2829<br />

Immune-mediated delayed-type hypersensitivity (DTH) responses to both<br />

virion proteins <strong>and</strong> myelin autoepitopes indicate simultaneous immunity to virus<br />

<strong>and</strong> autoimmunity to myelin epitopes. Immune-mediated destruction of myelin<br />

could arise by innocent byst<strong>and</strong>er destruction of myelin after immune-mediated<br />

attack directed toward virus epitopes within myelin sheaths. However, approximately<br />

4 weeks after disease onset, T cell responses to myelin epitopes arise in an<br />

ordered temporal progression. 29<br />

Lack of crossreactivity between TMEV <strong>and</strong><br />

myelin epitopes indicates that CNS autoimmunity arises by epitope spreading<br />

similar to R-EAE. 29<br />

Syngeneic <strong>transplantation</strong> from uninfected donor mice into mice with TMEV<br />

results in a high early mortality with an increased CNS viral titer (unpublished<br />

data). Allogeneic <strong>transplantation</strong> from uninfected disease-resistant donor strains

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