Theiler's virus infection of beta 2-microglobulin-deficient mice

Role of CD8 T cells in primary Chlamydia infection

The role of CD4 and CD8 T cells in primary Chlamydia trachomatis pneumonia was investigated by using in vivo depletion techniques to eliminate T-cell populations. Reduction of either CD4 T cells or CD8 T cells caused a significant increase in organism burden in the lungs, as measured by both quantitative culture and detection of chlamydial antigen on day 14 postinfection. Chlamydia-specific antibody levels in plasma or antigen-induced gamma interferon (IFN-gamma) production by spleen cells was dramatically reduced by depletion of CD4 cells. The reduction in IFN-gamma achieved by depletion of CD8 cells did not reach statistical significance. In the survival studies, depletion of CD4 cells led to a significant increase in mortality. Although there was a trend toward higher mortality, depletion of CD8 cells did not significantly increase mortality. The role of CD8 T cells in host defense was clarified in studies using beta 2-microglobulin-deficient (major histocompatibility class I antigen-deficient, C1D) mice which are defective in CD8 T-cell function. In this model, a significant increase in organism burden was seen during infection in C1D mice compared with that C57BL/6 controls and a significant increase in mortality was observed as well. However, surviving C1D mice were able to clear the infection by day 34. C1D mice had increased numbers of CD4 T cells in both the spleen and the lungs during infection compared with those of C57BL/6 controls. IFN-gamma in C57BL/6 mice was produced by both CD4 and CD8 cells. Thus, there is a protective role for both CD4 and CD8 cells in host defense against Chlamydia infection, but the former appear to be dominant.

Protection of SJL/J mice from demyelinating disease mediated by Theiler's murine encephalomyelitis virus

Intracerebral infection with the DA strain of Theiler's murine encephalomyelitis virus induces a chronic demyelinating disease in SJL/J mice. Intraperitoneal inoculation with either the wild-type DA virus or an attenuated variant virus of DA, H7A6-2, results in protection from development of chronic demyelinating disease. Protective anti-viral immune responses result in reduced viral titers and decreased inflammation in the central nervous system within the first week following intracerebral challenge with virus. Development of protective immunity requires the presence of B cells and CD4+ T cells but does not require CD8+ T cells. High titers of serum anti-viral IgG and neutralizing antibodies are induced following the intraperitoneal inoculation with the DA virus or H7A6-2 virus prior to challenge. While protection could not be transferred with immune serum from DA virus-infected mice or neutralizing monoclonal antibodies, protection was correlated with increased numbers of DA virus-specific plasma cells in the central nervous system within the first week following intracerebral challenge. Protected mice also had enhanced levels of anti-DA virus IgG and neutralizing antibodies in the cerebral spinal fluid by 1 week following intracerebral challenge with DA virus. Thus, we conclude that vaccination with live virus results in protection from chronic demyelinating disease by inducing immune responses which are manifested in the central nervous system and rapidly clear infection after intracerebral challenge with DA virus.

FVB mice transgenic for the H-2Db gene become resistant to persistent infection by Theiler's virus

The DA strain of Theiler's virus causes a persistent infection of the white matter of the spinal cord with chronic inflammation and primary demyelination. Inbred strains of mice differ greatly in their susceptibility to this disease. It has been shown that both viral persistence and demyelination are controlled mainly by a gene located in the H-2D region. This raised the possibility that the H-2D gene itself controls viral persistence, which in turn determines demyelination. In the present work we introduced the H-2Db gene of resistant C57BL/6 mice into the genome of susceptible H-2q FVB mice and showed that the FVB mice become resistant to persistence of the infection and did not develop inflammatory lesions.

Chimeric Theiler's virus with altered tropism for the central nervous system

Theiler's virus is a neurotropic murine picornavirus which, depending on the strain, causes either an acute encephalitis or a persistent demyelinating disease. Following intracranial inoculation, the demyelinating strains infect sequentially the grey matter of the brain, the grey matter of the spinal cord, and finally the white matter of the spinal cord, where they persist and cause chronic demyelination. The neurovirulent strains cause a generally fatal encephalitis with lytic infection of neurons. The study of chimeric Theiler's viruses, obtained by recombining the genomes of demyelinating and neurovirulent strains, has shown that the viral capsid contains determinants for persistence and demyelination. In this article we describe the recombinant virus R5, in which the capsid protein VP1 and a small portion of protein 2A come from the neurovirulent GDVII strain and the rest of the genome comes from the persistent DA strain. The capsid of virus R5 also contains one mutation at amino acid 34 of VP3 (Asn-->His). Virus R5 does not persist in the central nervous system (CNS) of immunocompetent SJL/J or BALB/c mice. However, it replicates efficiently and persists in the CNS of BALB/c nu/nu mice, showing that its growth in the CNS is not impaired. In BALB/c nu/nu mice, whereas virus DA causes mortality with large amounts of viral antigens in the white matter of the spinal cord, virus R5 does not kill the animals, persists in the neurons of the grey matter of the brain, and never reaches the white matter of the spinal cord. This phenotype is due to the chimerism of the capsid and/or to the mutation in VP3. These results indicate that the capsid plays an important role in the characteristic migration of Theiler's virus within the CNS.

Influence of deletion of T cell receptor V beta genes on the Theiler's virus model of multiple sclerosis

To determine the role of TCR V beta genes in a model of multiple sclerosis (MS), we studied Theiler's virus infection in congenic mice with deletion of TCR V beta chromosome. Congenic mice expressing the V beta a [50% deletion of TCR V beta] or V beta c 70% deletion of TCR V beta] haplotype were generated in mice resistant [B10 (H-2b)], intermediate [B10.K (H-2k), B10.RIII (H-2r)] or susceptible [B10.S (H-2s), and B10.Q (H-2q)] to Theiler's virus induced demyelination. Deletion of TCR V beta genes (V beta a or V beta c) did not convert B10 or B10.K congenic mice to susceptibility. In contrast, congenic B10.RIII-V beta c developed prominent demyelination and 10- to 100-fold increase in virus-antigen expression in spinal cord compared to B10.RIII mice. No effect on the extent of demyelination was observed in B10.S-V beta a, B10.S-V beta c or B10.Q-V beta c mice. These experiments illustrate the critical interactions between MHC, TCR, and background genes in susceptibility to immune-mediated disease.

Divergence between cytotoxic effector function and tumor necrosis factor alpha production for inflammatory CD4+ T cells from mice with Sendai virus pneumonia

Sendai virus pneumonia in beta 2-microglobulin-deficient [beta 2-m(-/-)] mice lacking CD8+ T cells is characterized by the development of CD4+ cytotoxic T lymphocytes that can be recovered directly from the respiratory tract. These CD4+ cytotoxic T lymphocytes are not found in beta 2-m (+/+) mice, though inflammatory CD4+ T cells from both beta 2-m (-/-) and beta 2-m (+/+) mice produce substantial amounts of tumor necrosis factor alpha. Blocking experiments with a monoclonal antibody that also inhibits tumor necrosis factor beta show that the secreted forms of these two cytokines are not responsible for virus-specific killing of class II major histocompatibility complex-compatible targets. Comparison of electron micrographs indicates that the CD4+ effectors from the beta 2-m (-/-) mice are potent inducers of apoptosis, while this is not the case for the beta 2-m (+/+) CD4+ set. These experiments further define the functional status of virus-specific CD4+ T cells responding in vivo in the presence or absence of CD8+ effectors.

Class I-deficient resistant mice intracerebrally inoculated with Theiler's virus show an increased T cell response to viral antigens and susceptibility to demyelination

Intracerebral inoculation of Theiler's murine encephalomyelitis virus (TMEV) results in immune-mediated demyelination in susceptible mouse strains. The histology of TMEV-induced demyelination is similar to that seen in patients suffering from multiple sclerosis. It was previously shown that the susceptibility of mice to TMEV-induced demyelination in certain strain combinations is closely associated with the major histocompatibility complex (MHC) class I locus. Here we examine disease susceptibility of beta 2-microglobulin (beta 2M)-deficient transgenic mice lacking class I expression and functional CD8+ T cells. In contrast to TMEV-infected parental C57BL/6 mice, the transgenics develop high levels of virus-specific DTH and T cell proliferation accompanied by an increased frequency of central nervous system (CNS) demyelinating lesions. However, clinical signs of demyelination were not noted. Neither antibody titer nor viral persistence were significantly affected in the beta 2M-deficient mice. These results suggest that in the absence of functional class I/CD8+ cells, the class II-restricted T cell response to TMEV is enhanced and CNS pathogenesis is heightened, although the level is not severe enough to result in clinical disease. When the TMEV-infected mice were subcutaneously immunized with virus, however, the beta 2M-deficient mice displayed clinical symptoms. Therefore, our results strongly suggest that CD8+ T cells do not directly contribute to CNS demyelination. In contrast, such T cells appear to be primarily involved in down-regulation of a potentially damaging CD4+ T cell response in resistant animals, although some of the T cells may play a role in clearing viral persistence in the CNS, resulting in the protection of the host from viral demyelination.

Virus infections in mice with targeted gene disruptions

The experimental dissection of the ways that the various cells and molecules of the immune system interact to promote virus clearance has been greatly facilitated by the availability of mice with targeted disruptions of key genes. New insights are emerging, and details of host resistance mechanisms that could only be inferred for the in vivo situation are now being clearly established.

MHC class I-deficient mice

A great deal has already been learned from the analysis of beta 2m-mutant mice, but it is clear that a great deal remains to be learned. A significant (though unanticipated) problem with this model system is that it is functionally leaky: residual functional class I expression can be detected in beta 2m- mice, and small numbers of functional CD8+ lymphocytes are present in the animals. In many cases, this has frustrated the initial attempts at obtaining immediate definitive resolution of important questions regarding the function of class I molecules. This has occurred primarily in instances in which the class I-deficient mice fail to express an expected phenotype--for example, in studies showing that beta 2m- mice make adequate protective immune responses against certain intracellular pathogens, and are able to reject some allogeneic tissues with a relatively normal pace. On the other hand, it appears that combining the use of beta 2m- mice with other methods (for example, antibody-mediated depletion of CD8+ T cells) is usually adequate to circumvent these difficulties. It remains to be seen whether other better class I deficiencies can be engineered--for example, large deletions of class I genes or mutations in transcription factors essential for class I gene expression. The extent of immunocompetence of beta 2m- mice was somewhat surprising. It was widely expected that class I-deficient mice would be exquisitely sensitive to many viral infections, though the results indicate that sensitivity varies dramatically with the virus and conditions of infection. However, it appears that in lieu of one major arm of the immune system, compensatory immune mechanisms are in many cases able to deal with infection. Similar conclusions are developing from the analysis of several other recently generated mutant mice. Nevertheless, the results indicate a very important role for class I-directed responses in clearing infections mediated by various viral and parasitic agents, particularly in the case of more severe conditions of infection. Although the class I-deficient mice were initially considered primarily a vehicle for analysis of the role of CD8+ T cells, evidence is accumulating that they manifest deficiencies in several other types of lymphocytes, including NK cells, TCR alpha beta+CD4-CD8- cells, and a subset of TCR gamma delta+ cells. This has been a boon for analysis of the development of these cells, but at the same time it has created difficulties in assigning a biological effect of the mutation to a specific lymphocyte deficiency.(ABSTRACT TRUNCATED AT 400 WORDS)