Abstract EN:

The central nervous system (CNS) is considered as a unique immune-privileged environment allowing a basal immune surveillance under physiological conditions, and restraining potentially deleterious inflammatory reactions in disease states. Nevertheless, an immune response may develop in the CNS during infectious or inflammatory diseases. The inflammatory immune reconstitution syndrome affecting the CNS (neuro-IRIS) is a particular setting in which tissue damage may be due to the infectious agent itself, the immune response it has generated, or both. CD8 T cells are key players of the adaptive immune response involved in the pathogenesis of infectious or inflammatory diseases of the CNS. Our first aim was to clarify the role of CD8 T cells in the pathophysiology of IRIS that occurred in HIV-infected patients developing progressive multifocal leukoencephalopathy (PML), a severe demyelinating disease due to reactivation of the JC polyomavirus. Analysis by histology, immunohistochemistry and confocal microscopy of PML-IRIS lesions shows the dominance of CD8 T cells, among which a cytotoxic subset engaged JC virus infected oligodendrocytes. During PML-IRIS, the CD8 T cell response is beneficial in controlling JC virus infection, at the cost of increased destruction of infected oligodendrocytes. These results illustrate the role of CD8 T cells in the clearance of a neurotropic pathogen, but also in the genesis of collateral tissue damage. We then developed a murine model of neuro-IRIS based on the transfer of naive CD8 T cells reactive to a neo-antigen selectively expressed in oligodendrocytes of lymphopenic mice. We show that lymphopenia is necessary but not sufficient to trigger CD8 T cell-mediated CNS tissue damage. Development of neuro-IRIS also requires the overcoming of regulatory mechanisms, and the presence of CNS danger signals. These findings underscore the conditions necessary for the development of CNS tissue damage in a setting of immune recovery. This mouse model will help to test therapeutic strategies relevant for HIV-infected patients suffering from neuro-IRIS, aiming to modulate the deleterious immune reconstitution, without dampening it. The development of CNS tissue damage implies the migration of encephalitogenic cells across the blood-brain barrier. Little is known about adhesion molecules involved in the migration of CD8 T cells to the CNS. Using a panel of monoclonal antibodies blocking adhesion molecules or their ligands, we show in a murine model of CNS autoimmunity that migration of CD8 T cells is dependent on the integrin a4ß1. We further suggest that VCAM-1 is probably not the only ligand for a4ß1, and that other molecules may be involved. The identification of additional molecules specifically implicated in the migration of encephalitogenic cell populations may raise the potential for selective control of their trafficking into the brain, preserving better preserve the immune surveillance of the CNS. Ultimately, our work based on observations of neurological inflammation in both animal models and Humans helps to increase the knowledge on the mechanisms of migration and pathogenicity of CD8 T cells in the CNS.