Virus encoding an encephalitogenic peptide protects mice from experimental allergic encephalomyelitis

Viral Infections and Autoimmune Disease: Roles of LCMV in Delineating Mechanisms of Immune Tolerance

Viral infections are a natural part of our existence. They can affect us in many ways that are the result of the interaction between the viral pathogen and our immune system. Most times, the resulting immune response is beneficial for the host. The pathogen is cleared, thus protecting our vital organs with no other consequences. Conversely, the reaction of our immune system against the pathogen can cause organ damage (immunopathology) or lead to autoimmune disease. To date, there are several mechanisms for virus-induced autoimmune disease, including molecular mimicry and bystander activation, in support of the “fertile field” hypothesis (terms defined in our review). In contrast, viral infections have been associated with protection from autoimmunity through mechanisms that include Treg invigoration and immune deviation, in support of the “hygiene hypothesis”, also defined here. Infection with lymphocytic choriomeningitis virus (LCMV) is one of the prototypes showing that the interaction of our immune system with viruses can either accelerate or prevent autoimmunity. Studies using mouse models of LCMV have helped conceive and establish several concepts that we now know and use to explain how viruses can lead to autoimmune activation or induce tolerance. Some of the most important mechanisms established during the course of LCMV infection are described in this short review.

Experimental autoimmune encephalomyelitis as a testing paradigm for adjuvants and vaccines

Experimental autoimmune encephalomyelitis (EAE) is an experimental model for multiple sclerosis. EAE can be induced by inoculation with central nervous system (CNS) proteins or peptides emulsified in complete Freund's adjuvant. Protection from EAE, enhancement of EAE or subclinical priming for EAE can occur as a result of either live viral infection or DNA immunization with molecular mimics of CNS proteins or peptides. Here we review the published data describing modulation of EAE through administration of various CNS proteins/peptides introduced via live virus or plasmid DNA and modulation of EAE through choice of adjuvant (immunostimulating agents).

Studies in the modulation of experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE), an experimental model for multiple sclerosis, can be induced through inoculation with several different central nervous system (CNS) proteins or peptides. Modulation of EAE, resulting in either protection from EAE or enhancement of EAE, can also be accomplished through either vaccination or DNA immunization with molecular mimics of self-CNS proteins. Previously published data on this method of EAE modulation will be reviewed. New data is presented, which demonstrates that EAE can also be modulated through the administration of the beta-(1,3)-D-glucan, curdlan. Dendritic cells stimulated by curdlan are involved in the differentiation of the interleukin-17 producing subset of CD4(+) T cells that are recognized effector cells in EAE. Using two different systems to study the effects of curdlan on EAE, it was found that curdlan increased the incidence of EAE and/or the severity of the disease course.

Potential triggers of MS

MS is an immune mediated disease of the central nervous system (CNS) characterized by demyelination, axonal damage and neurologic disability. The primary cause of this CNS disease remains elusive. Here we will address our current understanding of the role of viruses as potential environmental triggers for MS. Virus infections can act peripherally (outside the CNS) or within the CNS. The association of viral infections with demyelinating disease, in both animals and humans, will be discussed, as will the potential contributions of peripheral infection with Torque Teno virus, infection outside of and/or within the CNS with Epstein-Barr virus and infection within the CNS with Human Herpesvirus 6 to MS. An experimental animal model, Theiler's murine encephalomyelitis virus infection of susceptible strains of mice is an example of viral infections of the CNS as a prerequisite for demyelination. Finally, the proposition that multiple virus infections are required, which first prime the immune system and then trigger the disease, as a model where infections outside of the CNS lead to inflammatory changes within the CNS, for the development of a MS-like disease is explored.

A mathematical design of vector vaccine against autoimmune disease

Viruses have been implicated in the initiation, progression, and exacerbation of several human autoimmune diseases. Evidence also exists that viruses can protect against autoimmune disease. Several proposed mechanisms explain the viral effects. One mechanism is "molecular mimicry" which represents a shared immunologic epitope with a microbe and the host. We consider, using a simple mathematical model, whether and how a viral infection with molecular mimicry can be beneficial or detrimental for autoimmune disease. Furthermore, we consider the possibility of development of a vector therapeutic vaccine that can relieve autoimmune disease symptoms. Our findings demonstrate that vaccine therapy success necessitates (i) appropriate immune response function, (ii) appropriate affinities with self and non-self antigen, and (iii) a replicative vector vaccine. Moreover, the model shows that the viral infection can cause autoimmune relapses.

Targeting myelin proteolipid protein to the MHC class I pathway by ubiquitination modulates the course of experimental autoimmune encephalomyelitis

Relapsing-remitting experimental autoimmune encephalomyelitis (EAE), a multiple sclerosis model, is induced in mice by injection of myelin proteolipid protein (PLP) encephalitogenic peptide, PLP139-151, in adjuvant. In this study, prior to EAE induction, mice were vaccinated with a bacterial plasmid encoding a PLP-ubiquitin fusion (pCMVUPLP). During the relapse phase of EAE, clinical signs, histopathologic changes, in vitro lymphoproliferation to PLP139-151 and interferon-gamma levels were reduced in pCMVUPLP-vaccinated mice, compared to mock-vaccinated mice (controls). Lymphocytes from pCMVUPLP-vaccinated mice produced interleukin-4, a cytokine lacking in controls. Thus, pCMVUPLP vaccination can modulate the relapse after EAE induction.

Vaccines for multiple sclerosis: progress to date

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the CNS, characterized pathologically by a perivascular infiltrate consisting predominantly of T cells and macrophages. Although its aetiology remains unknown, several lines of evidence support the hypothesis that autoimmune mechanisms play a major role in the development of the disease. Several widely used disease-modifying agents are approved for the treatment of MS. However, these agents are only partially effective and their ability to attenuate the more progressive phases of the disease is not clear at this time. Therefore, there is a need to develop improved treatment options for MS. This article reviews the role of several novel, selective vaccine strategies that are currently under investigation, including: (i) T-cell vaccination (TCV); (ii) T-cell receptor (TCR) peptide vaccination; (iii) DNA vaccination; and (iv) altered peptide ligand (APL) vaccination. The administration of attenuated autoreactive T cells induces regulatory networks to specifically suppress pathogenic T cells in MS, a strategy named TCV. The concept of TCV was based on the experience of vaccination against aetiological agents of infectious diseases in which individuals are purposely exposed to an attenuated microbial pathogen, which then instructs the immune system to recognize and neutralize it in its virulent form. In regard to TCV, attenuated, pathogenic T cells are similarly used to instruct the immune system to recognize and neutralize disease-inducing T cells. In experimental allergic encephalomyelitis (EAE), an animal model for MS, pathogenic T cells use a strikingly limited number of variable-region elements (V region) to form TCR specific for defined autoantigens. Thus, vaccination with peptides directed against these TCR structures may induce immunoregulatory mechanisms, thereby preventing EAE. However, unlike EAE, myelin-reactive T cells derived from MS patients utilize a broad range of different V regions, challenging the clinical utility of this approach. Subsequently, the demonstration that injection of plasmid DNA encoding a reporter gene into skeletal muscle results in expression of the encoded proteins, as well as in the induction of immune responses in animal models of autoimmunity, was explored as another strategy to re-establish self-tolerance. This approach has promise for the treatment of MS and, therefore, warrants further investigation. APLs are molecules in which the native encephalitogenic peptides are modified by substitution(s) of one or a few amino acids critical for contact with the TCR. Depending on the substitution(s) at the TCR contact residues of the cognate peptide, an APL can induce immune responses that can protect against or reverse EAE. However, the heterogeneity of the immune response in MS patients requires further study to determine which patients are most likely to benefit from APL therapy. Other potential approaches for vaccines in MS include vaccination against axonal growth inhibitors associated with myelin, use of dendritic cells pulsed with specific antigens, and active vaccination against proinflammatory cytokines. Overall, vaccines for MS represent promising approaches for the treatment of this devastating disease, as well as other autoimmune diseases.

Myelin oligodendrocyte glycoprotein peptide-induced experimental allergic encephalomyelitis and T cell responses are unaffected by immunoproteasome deficiency

The inoculation of MOG peptides into C57BL/6 mice induces CD4(+) and CD8(+) T cells, and recent work has shown that adoptive transfer of the latter population, after extensive in vitro stimulation, can cause EAE in naïve recipient mice. Herein, we have evaluated the incidence and severity of EAE, and the induction of CD4(+) and CD8(+) T cells, following MOG peptide inoculation of wt mice and of LMP-2KO mice that lack an intact immunoproteasome, a cytoplasmic organelle that is induced by chronic inflammation and that may be important for the presentation of MHC class I epitopes to CD8(+) T cells. We report that EAE, evaluated by both clinical and histological criteria, is similar in LMP-2KO mice and wildtype C57B/6 mice (wt) in response to immunization with MOG peptides MOG(35-55) and MOG(40-54), suggesting that the immunoproteasome does not play a key role in the development of demyelinating disease. Furthermore, and consistent with previous reports, peptide-specific CD8(+) T cells were barely detectable in the CNS of peptide-immunized mice, although peptide-specific CD4(+) T cells were abundant. Therefore, we used a new technique to look for autoreactive CD8(+) T cells in MOG peptide-immunized mice, and we report the identification of CD4(+) and CD8(+) T cells that, as late as 19 days after peptide injection, are actively producing IFNgamma in vivo, in response to in vivo antigen contact.

Molecular mimicry, bystander activation, or viral persistence: infections and autoimmune disease

Virus infections and autoimmune disease have long been linked. These infections often precede the occurrence of inflammation in the target organ. Several mechanisms often used to explain the association of autoimmunity and virus infection are molecular mimicry, bystander activation (with or without epitope spreading), and viral persistence. These mechanisms have been used separately or in various combinations to account for the immunopathology observed at the site of infection and/or sites of autoimmune disease, such as the brain, heart, and pancreas. These mechanisms are discussed in the context of multiple sclerosis, myocarditis, and diabetes, three immune-medicated diseases often linked with virus infections.

Viral Delivery of an Epitope fromHaemophilus influenzaeInduces Central Nervous System Autoimmune Disease by Molecular Mimicry

Multiple sclerosis (MS) is an autoimmune CNS demyelinating disease in which infection may be an important initiating factor. Pathogen-induced cross-activation of autoimmune T cells may occur by molecular mimicry. Infection with wild-type Theiler's murine encephalomyelitis virus induces a late-onset, progressive T cell-mediated demyelinating disease, similar to MS. To determine the potential of virus-induced autoimmunity by molecular mimicry, a nonpathogenic neurotropic Theiler's murine encephalomyelitis virus variant was engineered to encode a mimic peptide from protease IV of Haemophilus influenzae (HI), sharing 6 of 13 aa with the dominant encephalitogenic proteolipid protein (PLP) epitope PLP(139-151). Infection of SJL mice with the HI mimic-expressing virus induced a rapid-onset, nonprogressive paralytic disease characterized by potent activation of self-reactive PLP(139-151)-specific CD4(+) Th1 responses. In contrast, mice immunized with the HI mimic-peptide in CFA did not develop disease, associated with the failure to induce activation of PLP(139-151)-specific CD4(+) Th1 cells. However, preinfection with the mimic-expressing virus before mimic-peptide immunization led to severe disease. Therefore, infection with a mimic-expressing virus directly initiates organ-specific T cell-mediated autoimmunity, suggesting that pathogen-delivered innate immune signals may play a crucial role in triggering differentiation of pathogenic self-reactive responses. These results have important implications for explaining the pathogenesis of MS and other autoimmune diseases.

Microorganisms and autoimmunity: making the barren field fertile?

Microorganisms induce strong immune responses, most of which are specific for their encoded antigens. However, microbial infections can also trigger responses against self antigens (autoimmunity), and it has been proposed that this phenomenon could underlie several chronic human diseases, such as type 1 diabetes and multiple sclerosis. Nevertheless, despite intensive efforts, it has proven difficult to identify any single microorganism as the cause of a human autoimmune disease, indicating that the 'one organism-one disease' paradigm that is central to Koch's postulates might not invariably apply to microbially induced autoimmune disease. Here, we review the mechanisms by which microorganisms might induce autoimmunity, and we outline a hypothesis that we call the fertile-field hypothesis to explain how a single autoimmune disease could be induced and exacerbated by many different microbial infections.

Virus-induced autoimmunity: potential role of viruses in initiation, perpetuation, and progression of T-cell-mediated autoimmune disease

Virus infections have been implicated in the initiation of multiple human autoimmune diseases. This article focuses on reviewing the role of viruses in initiation, progression, and perpetuation of autoimmune diseases. Various mechanisms by which virus infections can induce autoimmune responses including molecular mimicry, epitope spreading, direct bystander activation, and release of cryptic epitopes are discussed. Evidence implicating virus infections in the pathogenesis of various human autoimmune diseases is reviewed. Last, the characteristics of animal models that have been developed for the study of the potential role of viruses in the initiation and progression of autoimmune disease are reviewed.

Viruses and autoimmune disease--two sides of the same coin?

Some viruses have the ability to modulate the development of autoimmune diseases. Virus infections have long been associated with the exacerbation of autoimmune disease, however, there is also evidence that viruses can actually protect against autoimmune disease. Several experimental models have been developed to investigate how some virus infections can prime for and trigger autoimmunity whereas others ameliorate the pathway leading to clinical disease. It is possible that the type I interferons, via interleukin 12, provide the link between viruses and autoimmunity.

Multiple pathways to induction of virus-induced autoimmune demyelination: lessons from Theiler's virus infection

Infection of SJL mice with wild-type BeAn strain of Theiler's murine encephalomyelitis virus (TMEV) leads to CD4(+)T cell-mediated CNS demyelination characterized by the development of anti-myelin epitope autoimmune responses via epitope spreading during the chronic stage of disease. To exmine the feasibility of virus-encoded mimic epitopes to initiate CNS autoimmunity, we recently developed a molecular mimicry model of virus-induced demyelinating disease wherein a non-pathogenic variant strain of TMEV was engineered to encode a 30-mer peptide encompassing the immunodominant myelin proteolipid protein, PLP139-151, epitope. SJL mice infected intracerebrally with TMEV encoding either the native PLP139-151 determinant or various peptide mimics of the epitope develop an early onset demyelinating disease mediated by activated PLP139-151-specific Th1 cells. The autoimmune nature of this early-onset demyelinating disease is shown by the fact that induction of tolerance to the PLP139-151 peptide prevents clinical disease and associated PLP139-151-specific T cell responses without affecting T cell reactivity to virus epitopes. Most significantly, TMEV encoding a molecular mimic peptide derived from the Haemophilus influenzae bacteria, homologous at only six out of thirteen of the core amino acids, led to CNS disease. These studies provide conclusive evidence that virus-induced myelin-specific autoreactive T cells can be induced by molecular mimicry and provide a useful model to study the disease inducing ability of viruses encoding human-disease-related mimicry peptides.

DNA immunization and central nervous system viral infection

This chapter discusses the virus infections of the central nervous system (CNS) and DNA vaccines. Mild central nervous system (CNS) symptoms, such as headache and drowsiness, can result from systemically elevated cytokine levels and therefore are common in many virus infections, even in the absence of the infection of the CNS. CNS infection is quite unusual and is initiated either as a result of the viremia or, more rarely, as a result of neural spread. The poliovirus infects the anterior horn motor neurons of the spinal cord, causing poliomyelitis, the disease for which the virus is named. DNA vaccination is a relatively new entrant in the vaccine sweepstakes, but is viewed with optimism, for a number of reasons. DNA vaccines encoding the nucleoprotein from lymphocytic choriomeningitis virus can confer protection against the normally lethal intracranial challenge. In rabies, in a mouse model, immunization with plasmids encoding the rabies glycoprotein conferred complete protection against subsequent viral challenge. Several virus-induced CNS diseases may be explained by their triggering of autoimmunity. Experimental autoimmune encephalomyelitis is a well-characterized CNS disease induced by the administration of certain CNS proteins.

Myelin oligodendrocyte glycoprotein-DNA vaccination induces antibody-mediated autoaggression in experimental autoimmune encephalomyelitis

One strategy to reestablish self tolerance in autoimmune diseases is based on the use of DNA vaccination to induce ectopic expression of the target autoantigen. We assessed the potential of vaccination with a DNA construct encoding the myelin oligodendrocyte glycoprotein (MOG), an important candidate autoantigen in multiple sclerosis, to induce tolerance and protect against experimental autoimmune encephalomyelitis (EAE). Unexpectedly, mice vaccinated with MOG-DNA developed an exacerbated form of EAE when challenged with either MOG or an unrelated encephalitogen, myelin proteolipid protein. We demonstrate that this is due to the inability of DNA vaccination to tolerize the MOG-specific T cell response and to the concomitant induction of a cytopathic MOG-specific autoantibody response, which is pathogenic, enhancing demyelination, inflammation and disease severity. Our data suggest that tolerogenic strategies for autoimmune diseases based on DNA vaccination should be approached with caution, as the outcome is unpredictable.

Viruses as triggers of autoimmunity: facts and fantasies

Autoimmunity has been proposed as the cause of several human chronic inflammatory diseases, and recent animal studies show that viruses can induce autoimmune disease. These studies demonstrate how viruses might misdirect the immune system, and here we discuss critically the evidence that similar phenomena may lead to human disease.

Infection with a recombinant vaccinia virus encoding myelin proteolipid protein causes suppression of chronic relapsing-remitting experimental allergic encephalomyelitis

Mice infected with a recombinant vaccinia virus (VVplp) encoding the myelin proteolipid protein (PLP) and then challenged with the encephalitogenic peptide, PLP139-151, developed a more severe acute attack vs. control mice. Following this initial acute attack, vaccinated mice had significantly less clinical disease (relapses) than control vaccinated or mock vaccinated mice. Control mice developed a relapsing-remitting disease with severe clinical relapses. During the remission state in VVplp vaccinated mice, histopathologic changes were markedly reduced in the central nervous system (CNS) vs. control vaccinated or unvaccinated mice. Inflammation was mainly limited to the meninges with a reduction of mononuclear cells in the parenchyma of the spinal cord in VVplp vaccinated and PLP139-151 challenged mice vs. control mice where inflammatory changes with demyelination was observed. During the remission period an increase in IL-4 was seen. In addition, there was significantly less T cell proliferation to PLP139-151 that was confirmed by an in vivo measurement of T cell reactivity, DTH responses. This suggests that the almost permanent remission state was dictated by a decreased responsiveness to PLP139-151 in VVplp vaccinated mice.

Inhibition of allergic encephalomyelitis in marmosets by vaccination with recombinant vaccinia virus encoding for myelin basic protein

A primary demyelinating form of experimental allergic encephalomyelitis (EAE) resembling human multiple sclerosis (MS) occurs in Callithrix jacchus marmosets following immunization with human white matter. Participation of a T-cell immune response against myelin basic protein (MBP) in this disease model is supported by observations of increased reactivity against MBP in PBMC and of adoptive transfer of an inflammatory form of EAE by MBP-reactive T-cells. To evaluate the effects of ectopic presentation of MBP on marmoset EAE, animals were vaccinated prior to induction of EAE by subcutaneous injection of attenuated strains of vaccinia virus genetically engineered to contain either the entire coding sequence for human MBP (vT15) or the equine herpes virus glycoprotein gH gene (vAbT249). Vaccination with vT15 was followed by transient cytoplasmic and surface membrane expression of MBP in circulating PBMC (15-45 days). The onset of clinical EAE after immunization (pi) was markedly delayed in vT15-vaccinated animals (37-97 days pi, n = 4) compared to vAbT249-vaccinated controls (14-18 days pi, n = 3). Proliferative responses against MBP but not against vaccinia antigens or phytohemagglutinin were suppressed in protected animals. Thus, development of attenuated live viruses carrying genes for myelin antigens could be useful for induction of immunologic tolerance and for modulation of autoimmune demyelination.