The principal objectives of this study are two-fold: 1) to determine host and viral factors that influence the genetically controlled resistance of inbred mouse strains to street rabies virus (SRV) and 2) to determine the mechanism(s) by which recombinant vaccines expressing different structural proteins of rabies virus protect highly susceptible strains of mice against lethal infection. Cytotoxic T lymphocyte (CTL) studies have shown that susceptible strains of mice inoculated with either lethal or non-lethal concentrations of SRV have identical splenic CTL activities during the course of their infections. Passive transfer experiments and CTL assays with the same population of rabies virus immune spleen cells revealed that there was no correlation between the ability of the cells to protect naive animals from infection and the capacity of the cells to express CTL activity. A direct correlation with survival did exist in the concentration of anti-rabies virus neutralizing antibody that was produced by the transferred cells and was present in the serum of the recipient animals following cell transfer and just prior to their infection with SRV. Studies with recombinant vaccines expressing the rabies virus nucleoprotein (NP) revealed the mice vaccinated via tailscratch were well protected against a lethal rabies virus infection for up to 30 wks postvaccination. Immunological studies determined that the NP does not elicit neutralizing antibody or CTLs. Furthermore, target cells infected with recombinants expressing the NP are not lysed by rabies immune cells. To date the mechanism(s) of resistance elicited by the rabies virus NP is unknown. Recent studies have shown that immunodeficient athymic HSDnu/nu mice did not develop rear leg paralysis following infection with SRV. In contrast, immunocompetent HSDnu/+mice become paralyzed. HSDnu/nu mice reconstituted with 1X108 normal HSDnu/+ spleen cells and challenged one day later with SRV developed rear leg paralysis. HSDnu/nu mice reconstituted with normal HSDnu/+ spleen cells treated with anti-Thy 1.2+ plus complement prior to transfer failed to develop paralysis following SRV infection. Histological studies revealed perivascular mononuclear cell infiltration (PMCI) in the white matter of thalamus, hypothalamus, midbrain and pons of HSDnu/nu mice that had been reconstituted with normal spleen cells and challenged with SRV. Similar PMCI was not observed in animals that received SRV only or cells only. Immunohistochemical studies revealed both CD4+ and CD8+ T lymphocytes and Mac-1+ cells in areas of the brain in which PMCI was detected. Similar cells were rarely observed in the control groups. In HSDnu/nu mice that had received normal cells and SRV, a diffuse CD8+ T lymphocyte infiltration was detected in the parenchymatous tissue in the identical areas in which PMCI occurred. CD4+ T lymphocyte infiltration into parenchymatous tissue was never observed. We are continuing to investigate the importance of CTLs in resolving rabies infections within the CNS, the mechanisms of immunity induced by recombinant vaccines expressing the rabies NP, and the influence of hormones on the activation of virus is persistently infected animals.
