JHM virus (JHMV) infection results in an acute encephalomyelitis accompanied by primary demyelination. During acute disease a vigorous, but partially ineffective, immune response occurs within the central nervous system (CNS). The inability to effect sterilizing immunity results in persistent CNS infection and chronic ongoing demyelination with many pathological hallmarks similar to multiple sclerosis. Two predominant effectors of virus clearance have been identified: cytotoxic T lymphocyte (CTL) mediated cytolysis and interferon gamma (IFN-gamma). Our working hypothesis is that CD8+ T cells, using a combination of perforin mediated cytolysis and IFN-gamma secretion are the major immune effector systems which prevent JHMV-induced chronic demyelination. To understand the role of the immune response in clearing virus from the cells which support infection (astrocytes, oligodendroglia and microglia) and thereby define the components effective in preventing persistent infection and chronic disease, this project has two aims. The first analyzes the contribution of perforin mediated cytotoxicity. This is the major effector in virus clearance from astrocytes and microglia. To accomplish is goal CTL from IFN-gamma KO (GKO) mice will be transferred to infected SCID, GKO/perforin KO (GKO/PKO) and PKO recipients. GKO CTL exhibit excellent perforin mediated cytotoxicity but secrete no IFN-gamma. CTL from GKO donors will also be transferred into infected transgenic mice expressing the restriction element (L/d) exclusively on oligodendroglia.
The second aim determines the contribution of IFN-gamma to viral clearance and persistence. IFN-gamma appears to be effector mechanism involved in virus clearance from oligodendroglia. This will be accomplished by the transfer of CTL from PKO donors into infected SCID, PKO/GKO and GKO recipients. Virus load, specific cell types protected and progression to chronic infection and demyelination will be analyzed. The ability of CTL derived IFN-gamma to alter replication in oligodendroglia will be examined by transfers of PKO donor CTL into transgenic mice which express L/d on oligodendroglia. The ability of IFN-gamma to modify infection in oligodendroglia and astrocytes will be examined by expressing a dominant negative IFN-gamma alpha chain receptor transgene under the control of the PLP and GFAP promoters. Transgene expression will render these cells specifically resistant to IFN-gamma signaling events. Finally, transient IFN-gamma expression from infected cells, driven by a DI vector, will determine the effects of IFN-gamma on early progression of disease to chronic demyelination.
