Anergy in vivo: down-regulation of antigen-specific CD4+ Th1 but not Th2 cytokine responses

Emerging Therapeutics for Immune Tolerance: Tolerogenic Vaccines, T cell Therapy, and IL-2 Therapy

Autoimmune diseases affect roughly 5-10% of the total population, with women affected more than men. The standard treatment for autoimmune or autoinflammatory diseases had long been immunosuppressive agents until the advent of immunomodulatory biologic drugs, which aimed at blocking inflammatory mediators, including proinflammatory cytokines. At the frontier of these biologic drugs are TNF-α blockers. These therapies inhibit the proinflammatory action of TNF-α in common autoimmune diseases such as rheumatoid arthritis, psoriasis, ulcerative colitis, and Crohn's disease. TNF-α blockade quickly became the "standard of care" for these autoimmune diseases due to their effectiveness in controlling disease and decreasing patient's adverse risk profiles compared to broad-spectrum immunosuppressive agents. However, anti-TNF-α therapies have limitations, including known adverse safety risk, loss of therapeutic efficacy due to drug resistance, and lack of efficacy in numerous autoimmune diseases, including multiple sclerosis. The next wave of truly transformative therapeutics should aspire to provide a cure by selectively suppressing pathogenic autoantigen-specific immune responses while leaving the rest of the immune system intact to control infectious diseases and malignancies. In this review, we will focus on three main areas of active research in immune tolerance. First, tolerogenic vaccines aiming at robust, lasting autoantigen-specific immune tolerance. Second, T cell therapies using Tregs (either polyclonal, antigen-specific, or genetically engineered to express chimeric antigen receptors) to establish active dominant immune tolerance or T cells (engineered to express chimeric antigen receptors) to delete pathogenic immune cells. Third, IL-2 therapies aiming at expanding immunosuppressive regulatory T cells in vivo.

Immune Tolerance for Autoimmune Disease and Cell Transplantation

The undesired destruction of healthy cells, either endogenous or transplanted, by the immune system results in the loss of tissue function or limits strategies to restore tissue function. Current therapies typically involve nonspecific immunosuppression that may prevent the appropriate response to an antigen, thereby decreasing humoral immunity and increasing the risks of patient susceptibility to opportunistic infections, viral reactivation, and neoplasia. The induction of antigen-specific immunological tolerance to block undesired immune responses to self- or allogeneic antigens, while maintaining the integrity of the remaining immune system, has the potential to transform the current treatment of autoimmune disease and serve as a key enabling technology for therapies based on cell transplantation.

Monocyte-Derived Suppressor Cells in Transplantation

Myeloid-derived suppressor cells (MDSC) are cells of myeloid origin with enhanced suppressive function. They are negative regulators of the immune responses and comprise a heterogeneous mixture of immunosuppressive cells of monocytic (M-MDSC) and granulocytic (G-MDSC) origin. A more recent nomenclature proposes the term "suppressive monocyte derived cells" (suppressive MCs) to define CSF1/CSF2-dependent mouse suppressor cells that develop from common monocyte progenitors (cMoPs) after birth. Here, we review the literature about monocytic-derived cells with demonstrated suppressor function in vitro and in vivo within the context of solid organ transplantation.

Effect of the innate immune response on development of Theiler's murine encephalomyelitis virus-induced demyelinating disease

Theiler's murine encephalomyelitis virus (TMEV) infection of susceptible mice leads to the development of demyelinating disease in the central nervous system (CNS) associated with an inflammatory immune response. The demyelinating disease in mice has similarities to multiple sclerosis in humans and is used as an experimental model for the human disease. The innate immune response initiates the immune response to TMEV through innate immune receptors on cells that recognize components of the virus and activate intracellular signaling that leads to the expression of innate immune cytokines, chemokines, and effector molecules. The innate immune response directly affects the development of the adaptive immune response, especially the T cell response, which mediates viral clearance. However, infection of Swiss Jim Laboratory (SJL) mice with TMEV leads to a persistent virus infection of the microglia/macrophage in the CNS which contributes to the development of demyelinating disease. Susceptibility to demyelinating disease has been linked to the T cell response against the virus. However, the current studies will examine the role of the innate immune response to TMEV and the affect it has on the adaptive immune response and development of demyelinating disease following TMEV infection. The innate immune cytokines, chemokines, and effector molecules as well as the innate immune cells, both CNS resident and infiltrating peripheral cells, all contribute to the innate immune response following TMEV and may affect susceptibility to demyelinating disease.

Antigen-specific tolerance by autologous myelin peptide-coupled cells: a phase 1 trial in multiple sclerosis

Multiple sclerosis (MS) is a devastating inflammatory disease of the brain and spinal cord that is thought to result from an autoimmune attack directed against antigens in the central nervous system. The aim of this first-in-man trial was to assess the feasibility, safety, and tolerability of a tolerization regimen in MS patients that uses a single infusion of autologous peripheral blood mononuclear cells chemically coupled with seven myelin peptides (MOG1-20, MOG35-55, MBP13-32, MBP83-99, MBP111-129, MBP146-170, and PLP139-154). An open-label, single-center, dose-escalation study was performed in seven relapsing-remitting and two secondary progressive MS patients who were off-treatment for standard therapies. All patients had to show T cell reactivity against at least one of the myelin peptides used in the trial. Neurological, magnetic resonance imaging, laboratory, and immunological examinations were performed to assess the safety, tolerability, and in vivo mechanisms of action of this regimen. Administration of antigen-coupled cells was feasible, had a favorable safety profile, and was well tolerated in MS patients. Patients receiving the higher doses (>1 × 10(9)) of peptide-coupled cells had a decrease in antigen-specific T cell responses after peptide-coupled cell therapy. In summary, this first-in-man clinical trial of autologous peptide-coupled cells in MS patients establishes the feasibility and indicates good tolerability and safety of this therapeutic approach.

Recurrent herpetic stromal keratitis in mice: a model for studying human HSK

Herpes simplex virus 1 (HSV-1) infection of the cornea leads to a potentially blinding disease, termed herpetic stromal keratitis (HSK) that is characterized by lesions of an immunoinflammatory nature. In spite of the fact that HSK typically presents as a recurrent disease due to reactivation of virus which latently infects the trigeminal ganglia, most murine studies of HSK have employed a primary and not recurrent model of the disease. This report documents the several recurrent models of HSK that have been developed and how data generated from these models differs in some important aspects from data generated following primary infection of the cornea. Chief among these differences is the fact that recurrent HSK takes place in the context of an animal that has a preexisting anti-HSV immune response, while primary HSK occurs in an animal that is developing such a response. We will document both differences and similarities that derive from this fundamental difference in these models with an eye towards possible vaccines and therapies that demonstrate promise in treating HSK.

Molecular mimicry as an inducing trigger for CNS autoimmune demyelinating disease

Summary:  Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS) that affects about 0.1% of the worldwide population. This deleterious disease is marked by infiltration of myelin‐specific T cells that attack the protective myelin sheath that surrounds CNS nerve axons. Upon demyelination, saltatory nerve conduction is disrupted, and patients experience neurologic deficiencies. The exact cause for MS remains unknown, although most evidence supports the hypothesis that both genetic and environmental factors contribute to disease development. Epidemiologic evidence supports a role for environmental pathogens, such as viruses, as potentially key contributors to MS induction. Pathogens can induce autoimmunity via several well‐studied mechanisms with the most postulated being molecular mimicry. Molecular mimicry occurs when T cells specific for peptide epitopes derived from pathogens cross‐react with self‐epitopes, leading to autoimmune tissue destruction. In this review, we discuss an in vivo virus‐induced mouse model of MS developed in our laboratory, which has contributed greatly to our understanding of the mechanisms underlying molecular mimicry‐induced CNS autoimmunity.

Preferential induction of protective T cell responses to Theiler's virus in resistant (C57BL/6 x SJL)F1 mice

Infection of the central nervous system (CNS) with Theiler's murine encephalomyelitis virus (TMEV) induces an immune-mediated demyelinating disease in susceptible mouse strains such as SJL/J (H-2(s)) but not in strains such as C57BL/6 (H-2(b)). In addition, it has been shown that (C57BL/6 × SJL/J)F1 mice (F1 mice), which carry both resistant and susceptible MHC haplotypes (H-2(b/s)), are resistant to both viral persistence and TMEV-induced demyelinating disease. In this study, we further analyzed the immune responses underlying the resistance of F1 mice. Our study shows that the resistance of F1 mice is associated with a higher level of the initial virus-specific H-2(b)-restricted CD8(+) T cell responses than of the H-2(s)-restricted CD8(+) T cell responses. In contrast, pathogenic Th17 responses to viral epitopes are lower in F1 mice than in susceptible SJL/J mice. Dominant effects of resistant genes expressed in antigen-presenting cells of F1 mice on regulation of viral replication and induction of protective T cell responses appear to play a crucial role in disease resistance. Although the F1 mice are resistant to disease, the level of viral RNA in the CNS was intermediate between those of SJL/J and C57BL/6 mice, indicating the presence of a threshold of viral expression for pathogenesis.

A critical role for virus-specific CD8(+) CTLs in protection from Theiler's virus-induced demyelination in disease-susceptible SJL mice

Theiler's murine encephalomyelitis virus (TMEV)-induced demyelinating disease (TMEV-IDD) is a relevant mouse model of multiple sclerosis. Infection of susceptible SJL/J mice leads to life-long CNS virus persistence and development of a chronic T cell-mediated autoimmune demyelinating disease triggered via epitope spreading to endogenous myelin epitopes. Potent CNS-infiltrating CD8(+) T cell responses to TMEV epitopes have previously been shown to be induced in both disease-susceptible SJL/J and resistant C57BL/6 mice, in which the virus is rapidly cleared. Specific tolerization of SJL CD8(+) T cells specific for the immunodominant TMEV VP3(159)(-)(166) epitope has no effect on viral load or development of clinical TMEV-IDD, but adoptive transfer of activated CD8(+) VP3(159)(-)(166)-specific T cell blasts shortly after TMEV infection to boost the early anti-viral response leads to clearance of CNS virus and protection from subsequent TMEV-IDD. These studies have important implications for vaccine strategies and treatment of chronic infections in humans.

Theiler's virus infection induces a predominant pathogenic CD4+ T cell response to RNA polymerase in susceptible SJL/J mice

Theiler's murine encephalomyelitis virus (TMEV)-induced immune-mediated demyelinating disease in susceptible mouse strains has been extensively investigated as a relevant model for human multiple sclerosis. Previous investigations of antiviral T-cell responses focus on immune responses to viral capsid proteins, while virtually nothing is reported on immune responses to nonstructural proteins. In this study, we have identified noncapsid regions recognized by CD4(+) T cells from TMEV-infected mice using an overlapping peptide library. Interestingly, a greater number of CD4(+) T cells recognizing an epitope (3D(21-36)) of the 3D viral RNA polymerase, in contrast to capsid epitopes, were detected in the CNS of TMEV-infected SJL mice, whereas only a minor population of CD4(+) T cells from infected C57BL/6 mice recognized this region. The effects of preimmunization and tolerization with these epitopes on the development of demyelinating disease indicated that capsid-specific CD4(+) T cells are protective during the early stages of viral infection, whereas 3D(21-36)-specific CD4(+) T cells exacerbate disease development. Therefore, protective versus pathogenic CD4(+) T-cell responses directed to TMEV appear to be epitope dependent, and the differences in CD4(+) T-cell responses to these epitopes between susceptible and resistant mice may play an important role in the resistance or susceptibility to virally induced demyelinating disease.

Molecular mechanisms of T-cell receptor and costimulatory molecule ligation/blockade in autoimmune disease therapy

SUMMARY

Pro-inflammatory CD4(+) T-cell-mediated autoimmune diseases, such as multiple sclerosis and type 1 diabetes, are hypothesized to be initiated and maintained by activated antigen-presenting cells presenting self antigen to self-reactive interferon-gamma and interleukin-17-producing CD4(+) T-helper (Th) type 1/Th17 cells. To date, the majority of Food and Drug Administration-approved therapies for autoimmune disease primarily focus on the global inhibition of immune inflammatory activity. The goal of ongoing research in this field is to develop both therapies that inhibit/eliminate activated autoreactive cells as well as antigen-specific treatments, which allow for the directed blockade of the deleterious effects of self-reactive immune cell function. According to the two-signal hypothesis, activation of a naive antigen-specific CD4(+) T cell requires both stimulation of the T-cell receptor (TCR) (signal 1) and stimulation of costimulatory molecules (signal 2). There also exists a balance between pro-inflammatory and anti-inflammatory immune cell activity, which is regulated by the type and strength of the activating signal as well as the local cytokine milieu in which the naive CD4(+) T cell is activated. To this end, the majority of ongoing research is focused on the delivery of suboptimal TCR stimulation in the absence of costimulatory molecule stimulation, or potential blockade of stimulatory accessory molecules. Therefore, the signaling pathways involved in the induction of CD4(+) T-cell anergy, as apposed to activation, are topics of intense interest.

Prospects for antigen-specific tolerance based therapies for the treatment of multiple sclerosis

A primary focus in autoimmunity is the breakdown of central and peripheral tolerance resulting in the survival and eventual activation of autoreactive T cells. As CD4(+) T cells are key contributors to the underlying pathogenic mechanisms responsible for onset and progression of most autoimmune diseases, they are a logical target for therapeutic strategies. One method for restoring self-tolerance is to exploit the endogenous regulatory mechanisms that govern CD4(+) T cell activation. In this review, we discuss tolerance strategies with the common goal of inducing antigen (Ag)-specific tolerance. Emphasis is given to the use of peptide-specific tolerance strategies, focusing on ethylene carbodiimide (ECDI)-peptide-coupled cells (Ag-SP) and nonmitogenic anti-CD3, which specifically target the T cell receptor (TCR) in the absence of costimulatory signals. These approaches induce a TCR signal of insufficient strength to cause CD4(+) T cell activation and instead lead to functional T cell anergy/deletion and activation of Ag-specific induced regulatory T cells (iTregs) while avoiding generalized long-term immunosuppression.

Distinctly different sensitivity in the induction and reversal of anergy of Th1 and Th2 cells

T cell anergy is one of the mechanisms of immunological tolerance. We examined in this study the distinct responses of Th1 and Th2 cells to in vitro anergic stimulation using Th1 and Th2 cells from two strains of T cell receptor transgenic mice. Proliferation of the Th2 cells was difficult to suppress by anergic stimulation, while that of Th1 cells was significantly inhibited even by weak stimulation. However, IL-4 production by Th2 cells was definitely reduced by anergic stimulation, although the inhibition level of IL-4 was lower than that of IFN-gamma production by Th1 cells. We also examined the reversal of anergy in both subsets. While both the anergized Th1 and Th2 cells responded to IL-2 stimulation, only the anergy of the Th2 cells could be reversed. This result indicates that progression of the cell cycle was not sufficient for anergy reversal in Th1 cells. Our findings indicate that the induction and reversal of T cell anergy might be affected by the distinct signaling features of Th1 and Th2 cells.

Induction of antigen specific peripheral humoral tolerance to cardiac myosin does not prevent CB3-mediated autoimmune myocarditis

Chronic myocarditis often progresses to dilated cardiomyopathy resulting in heart failure or cardiac transplantation. Viral infection is the most common cause of myocarditis and coxsackie B viruses (CBV) are the most frequently cited etiologic agents associated with myocarditis and cardiomyopathy. Additionally, CBV infections of genetically susceptible mice induce autoimmune myocarditis resembling human disease, including the development of autoantibodies to cardiac myosin. Herein, we describe experiments in which peripheral tolerance to cardiac myosin was induced by administration of antigen-coupled antigen presenting cells. While the antibody response to cardiac myosin following CB3 infection was reduced, the viral induction of clinical autoimmune myocarditis was not affected. Additionally, viral replication was unaffected by the reduced humoral response to cardiac myosin. Therefore, the humoral response to cardiac myosin is not required for the development of autoimmunity following infection of NOD mice. This work demonstrates the difficulty in using antigen specific tolerance as a course of treatment to prevent multivalent autoimmune disorders.

Creation of tolerogenic human dendritic cells via intracellular CTLA4: a novel strategy with potential in clinical immunosuppression

Activation of T lymphocytes requires the recognition of peptide-major histocompatibility complexes (MHCs) and costimulatory signals provided by antigen-presenting cells (APCs). It has been shown that T-cell activation without costimulation can lead to anergy. In this study, we developed a novel strategy to inhibit expression of B7 molecules (CD80/86) by transfecting APCs with a gene construct encoding a modified cytotoxic T lymphocyte antigen 4 (CTLA4) molecule (CTLA4-KDEL) that is targeted to the endoplasmic reticulum (ER). APCs expressing this construct failed to express CD80/86 on their surface, were unable to stimulate allogeneic and peptide-specific T-cell responses, and induced antigen-specific anergy of the responding T cells. Cells expressing CTLA4-KDEL do not up-regulate the indoleamine 2, 3-dioxygenase enzyme, unlike cells treated with soluble CTLA4-immunoglobin (Ig). This gene-based strategy to knock out surface receptors is an attractive alternative to using immature dendritic cells for preventing transplant rejection and treating of autoimmune diseases.

Innate immune response induced by Theiler's murine encephalomyelitis virus infection

Although the causative agents of human multiple sclerosis (MS) are not known, it is suspected that a viral infection may be associated with the initiation of the disease. Several viral disease models in mice have been studied to understand the pathogenesis of demeylination. In particular, Theiler's murine encephalomyelitis virus-induced demyelinating disease (TMEV-IDD) has been extensively studied as a relevant model. Various cytokines and chemokines are produced upon viral infection by different cell types, including antigen-presenting cells (APCs) such as macrophages; dendritic cells (DCs); and glial cells, such as astrocytes, microglia, and oligoden-drocytes. The upregulation of the corresponding molecules are also found in MS and are likely to play an important role in the protection and/or pathogenesis of chronic inflammatory demyelinating disease. In this review, the type of cells and molecules, gene-activation mechanisms as well as their potential roles in protection and pathogenesis will be discussed.

CTLA-4 Regulates Expansion and Differentiation of Th1 Cells Following Induction of Peripheral T Cell Tolerance

Intravenous treatment with Ag (peptide)-coupled, ethylene carbodiimide-fixed syngeneic splenocytes (Ag-SP) is a powerful method to induce anergy in vitro and peripheral T cell tolerance in vivo. In this study, we examined the effects of Ag-SP administration on T cell activity ex vivo and in vivo using OVA-specific DO11.10 TCR transgenic T cells. Although treatment with OVA323-339-SP resulted in a strong inhibition of peptide-specific T cell recall responses in vitro, examination of the immediate effects of Ag-SP treatment on T cells in vivo demonstrated that tolerogen injection resulted in rapid T cell activation and proliferation. Although there was an increase in the number of OVA-specific DO11.10 T cells detected in the lymphoid organs, these previously tolerized T cells were strongly inhibited in mounting proliferative or inflammatory responses upon rechallenge in vivo with peptide in CFA. This unresponsiveness was reversible by treatment with anti-CTLA-4 mAb. These results are consistent with the hypothesis that Ag-SP injection induces a state of T cell anergy that is maintained by CTLA-4 engagement.

Theiler's virus infection: a model for multiple sclerosis

Both genetic background and environmental factors, very probably viruses, appear to play a role in the etiology of multiple sclerosis (MS). Lessons from viral experimental models suggest that many different viruses may trigger inflammatory demyelinating diseases resembling MS. Theiler's virus, a picornavirus, induces in susceptible strains of mice early acute disease resembling encephalomyelitis followed by late chronic demyelinating disease, which is one of the best, if not the best, animal model for MS. During early acute disease the virus replicates in gray matter of the central nervous system but is eliminated to very low titers 2 weeks postinfection. Late chronic demyelinating disease becomes clinically apparent approximately 2 weeks later and is characterized by extensive demyelinating lesions and mononuclear cell infiltrates, progressive spinal cord atrophy, and axonal loss. Myelin damage is immunologically mediated, but it is not clear whether it is due to molecular mimicry or epitope spreading. Cytokines, nitric oxide/reactive nitrogen species, and costimulatory molecules are involved in the pathogenesis of both diseases. Close similarities between Theiler's virus-induced demyelinating disease in mice and MS in humans, include the following: major histocompatibility complex-dependent susceptibility; substantial similarities in neuropathology, including axonal damage and remyelination; and paucity of T-cell apoptosis in demyelinating disease. Both diseases are immunologically mediated. These common features emphasize the close similarities of Theiler's virus-induced demyelinating disease in mice and MS in humans.

Alloantigen presentation by ethylcarbodiimide-treated dendritic cells induces T cell hyporesponsiveness, and prolongs organ graft survival

Ethylcarbodiimide (ECDI) couples soluble antigens (Ag) to lymphoid cells bestowing tolerizing potential. We examined whether ECDI-treated allogeneic dendritic cells (DC) could promote Ag-specific T cell unresponsiveness and prolong graft survival. Exposure of murine myeloid DC to ECDI did not affect surface immunophenotype but reduced their ability to cluster with T cells, enhanced their apoptotic death, and markedly reduced their allostimulatory activity. Anti-donor proliferative and cytotoxic T cell responses of mice primed with ECDI-treated DC were markedly inhibited. Secretion of both Th1 (IFNgamma) and Th2 cytokines (IL-5, IL-10) was suppressed. Cardiac allograft survival in mice preconditioned with a single injection of ECDI-DC was prolonged significantly. These results indicate that ECDI-treated DC promote T cell unresponsiveness to donor alloAgs and prolong transplant survival. The effects are not associated with sparing of Th2 responses, but may reflect inhibitory effects of apoptotic donor DC on host immune reactivity.

Myosin Autoimmunity Is Not Essential for Cardiac Inflammation in Acute Chagas’ Disease

Infection with the protozoan parasite Trypanosoma cruzi leads to acute myocarditis that is accompanied by autoimmunity to cardiac myosin in susceptible strains of mice. It has been difficult to determine the contribution of autoimmunity to tissue inflammation, because other inflammatory mechanisms, such as parasite-mediated myocytolysis and parasite-specific immunity, are coincident during active infection. To begin to investigate the contribution of myosin autoimmunity to myocarditis, we selectively inhibited myosin autoimmunity by restoring myosin tolerance via injection of myosin-coupled splenocytes. This tolerization regimen suppressed the strong myosin-specific delayed-type hypersensitivity (DTH) that normally develops in infected mice, although it did not affect myosin-specific Ab production. Suppression of myosin autoimmunity had no effect on myocarditis or cardiac parasitosis. In contrast, myosin tolerization completely abrogated myocarditis in mice immunized with purified myosin, which normally causes severe autoimmune myocarditis. In this case, myosin-specific DTH and Ab production were significantly reduced. We also examined the contribution of T. cruzi-specific immunity to inflammation by injection of T. cruzi-coupled splenocytes before infection. This treatment reduced T. cruzi DTH, although there was no effect on parasite-specific Ab production. Interestingly, cardiac inflammation was decreased, cardiac parasitosis was significantly increased, and mortality occurred earlier in the parasite-tolerized animals. These results indicate that myosin-specific autoimmunity, while a potentially important inflammatory mechanism in acute and chronic T. cruzi infection, is not essential for inflammation in acute disease. They also confirm previous studies showing that parasite-specific cell-mediated immunity is important for myocarditis and survival of T. cruzi infection.

Effect of in vivo administration of anti-CTLA-4 monoclonal antibody and IL-12 on the induction of low-dose oral tolerance

Oral tolerance has been characterized as an immunological hyporesponsiveness to fed antigen. Previous studies have suggested that high-dose oral tolerance involves the preferential interaction of B7 with CTLA-4 on the T cell. To determine whether similar mechanisms are involved in the induction of low-dose oral tolerance, mice were treated with anti-CTLA-4 monoclonal antibody (MoAb), with or without IL-12, at the time of feeding. Results showed that anti-CTLA-4 MoAb alone failed to restore cellular proliferation, antibody titres and IFN-gamma levels; however, IL-4 cytokine levels in OVA-fed mice were partially restored. In contrast, administration of IL-12 along with anti-CTLA-4 MoAb to mice during feeding completely prevented the suppression of Th1 immune responses, as shown by increased serum IgG2a titres, IFN-gamma production and cell proliferation. These results suggest that blocking B7-CTLA-4 interactions in the presence of IL-12 prevents the induction of low-dose oral tolerance at the Th1 cell level.

Functional activation of myelin-specific T cells by virus-induced molecular mimicry

Molecular mimicry is the process by which T cells activated in response to determinants on an infecting microorganism cross-react with self epitopes, leading to an autoimmune disease. Normally, infection of SJL/J mice with the BeAn strain of Theiler's murine encephalomyelitis virus (TMEV) results in a persistent CNS infection, leading to a chronic progressive, CD4(+) T cell-mediated demyelinating disease. Myelin damage is initiated by T cell responses to virus persisting in CNS APCs, and progressive demyelinating disease (50 days postinfection) is perpetuated by myelin epitope-specific CD4(+) T cells activated by epitope spreading. We developed an infectious model of molecular mimicry by inserting a sequence encompassing the immunodominant myelin epitope, proteolipid protein (PLP) 139-151, into the coding region of a nonpathogenic TMEV variant. PLP139-TMEV-infected mice developed a rapid onset paralytic inflammatory, demyelinating disease paralleled by the activation of PLP139-151-specific CD4(+) Th1 responses within 10-14 days postinfection. The current studies demonstrate that the early onset demyelinating disease induced by PLP139-TMEV is the direct result of autoreactive PLP139-151-specific CD4(+) T cell responses. PLP139-151-specific CD4(+) T cells from PLP139-TMEV-infected mice transferred demyelinating disease to naive recipients and PLP139-151-specific tolerance before infection prevented clinical disease. Finally, infection with the mimic virus at sites peripheral to the CNS induced early demyelinating disease, suggesting that the PLP139-151-specific CD4(+) T cells could be activated in the periphery and traffic to the CNS. Collectively, infection with PLP139-151 mimic encoding TMEV serves as an excellent model for molecular mimicry by inducing pathologic myelin-specific CD4(+) T cells via a natural virus infection.

Bornavirus tropism and targeted pathogenesis: virus-host interactions in a neurodevelopmental model

Animal models provide unique opportunities to explore interactions between host and environment. Two models have been established based on Bornavirus infection that provide new insights into mechanisms by which neurotropic agents and/or immune factors may impact developing or mature CNS circuitry to effect complex disturbances in movement and behavior. Distinct losses in DA pathways in the adult infection model, and the associated dramatic movement disorder that accompanies it, make it an intriguing model for tardive dyskinesia and dystonic syndromes. The neuropathologic, physiologic, and neurobehavioral features of BDV infection of neonates indicate that it not only provides a useful model for exploring the mechanisms by which viral and immune factors may damage developing neurocircuitry, but also has significant links to the range of biologic, neurostructural, locomotor, cognitive, and social deficits observed in serious neuropsychiatric illnesses such as autism.

Virus-induced autoimmunity: epitope spreading to myelin autoepitopes in Theiler's virus infection of the central nervous system

Epidemiological studies indicate that host immunogenetics and history of infection, particularly by viruses, may be a necessary cofactor for the induction of a variety of autoimmune diseases. To date, however, there is no clear-cut evidence, either in experimental animal models or in human autoimmune disease, that supports either molecular mimicry (Wucherpfennig and Strominger, 1995; Fujinami and Oldstone, 1985) or a role for superantigens (Scherer et al., 1993) in the initiation of T cell-mediated autoimmunity. In contrast, the current data provide compelling evidence in support of a major role for epitope spreading in the induction of myelin-specific autoimmunity in mice persistently infected with TMEV. It is significant that two picornaviruses closely related to TMEV, coxsackievirus (Rose and Hill, 1996) and encephalomyocarditis virus (EMCV) (Kyu et al., 1992), have been similarly shown to persist (either the viral RNA or the infectious virus) in their target organs and have been associated with the development of chronic autoimmune diseases, including myocarditis and diabetes. Thus, inflammatory responses induced by viruses that trigger proinflammatory Th1 responses, and have the ability to persist in genetically susceptible hosts, may lead to chronic organ-specific autoimmune disease via epitope spreading. Epitope spreading has important implications for the design of antigen-specific therapies for the potential treatment of MS and other autoimmune diseases. This process indicates that autoimmune diseases are evolving entities and that the specificity of the effector autoantigen-specific T cells varies during the chronic disease process. Our experiments employing tolerance in R-EAE clearly indicate that antigen-specific treatment of ongoing disease is possible for preventing disease relapses, provided the proper relapse-associated epitope is targeted (Vanderlugt et al., 1999). However, the ability to identify relapse-associated epitopes in humans will be a difficult task because immunodominance will vary in every individual. The use of costimulatory antagonists that can induce anergy without requiring prior knowledge of the exact epitopes (Miller et al., 1995b), or the use of therapies that induce bystander suppression (Nicholson et al., 1997; Brocke et al., 1996), may thus be more practical current alternative therapies for the treatment of human autoimmune disease.

Functional role of epitope spreading in the chronic pathogenesis of autoimmune and virus-induced demyelinating diseases

These results support a model of epitope spreading (Figure 4) wherein localized virus-specific T cell-mediated inflammatory processes lead to the recruitment/activation of CNS-resident APCs which can serve both as effector cells for myelin destruction and as APCs which efficiently process/present endogenous self epitopes to autoreactive T cells. Thus, inflammatory responses induced by viruses which trigger pro-inflammatory Th1 responses and have the ability to persist in genetically susceptible hosts, may lead to chronic organ-specific autoimmune disease via epitope spreading. Regardless of the specificity of the T cells (myelin peptides in R-EAE or TMEV epitopes in TMEV-IDD) responsible for initiating myelin destruction, epitope spreading plays an important contributory role in the chronic disease process in genetically susceptible SJL mice. Epitope spreading has obvious important implications to the design of antigen-specific therapies for the potential treatment of MS and other autoimmune diseases. This process indicates that autoimmune diseases are evolving pathologies and that the specificity of the effector autoantigen-specific T cells varies during the chronic disease process.

Myelin-specific tolerance attenuates the progression of a virus-induced demyelinating disease: implications for the treatment of MS

Theiler's murine encephalomyelitis virus-induced demyelinating disease (TMEV-IDD), a multiple sclerosis (MS) model, is a central nervous system (CNS) demyelinating disease characterized by early peripheral T cell responses to virus epitopes which spreads to myelin epitopes during chronic disease. We show that CD4(+) T cells isolated from the spinal cords of chronically infected SJL mice proliferate and secrete pro-inflammatory cytokines upon in vitro challenge with both TMEV epitopes and proteolipid protein (PLP(139-151)). Importantly, myelin-specific tolerance induced by intravenous administration of MP4, a fusion of the myelin proteins myelin basic protein (MBP) and PLP, to SJL mice with ongoing TMEV-IDD attenuated disease progression and resulted in significantly less demyelination and decreased inflammatory cell infiltration in the CNS. Paradoxically, peptide-specific splenic T cell proliferative and IFN-gamma responses were enhanced in the tolerized mice. Collectively, these results indicate that myelin-specific T cell responses contribute to chronic disease progression in this virus-induced model of MS, and suggest caution in the use of antigen-specific tolerance for treatment of ongoing autoimmune disease.

Borna disease virus infection of adult and neonatal rats: models for neuropsychiatric disease

Animal models provide unique opportunities to explore interactions between host and environment. Two models have been established based on Borna disease virus infection that provide new insights into mechanisms by which neurotropic agents and/or immune factors may impact developing or mature CNS circuitry to effect complex disturbances in movement and behavior. Note in press: Since this chapter was submitted, several manuscripts have been published that extend findings reported here and support the relevance of BDV infections of neonatal Lewis rats as models for investigating mechanisms of neurodevelopmental damage in autism. Behavioral abnormalities, including disturbed play behavior and chronic emotional overactivity, have been described by Pletnikov et al. (1999); inhibition of responses to novel stimuli were described by Hornig et al. (1999); loss of Purkinje cells following neonatal BDV infection has been demonstrated by Eisenman et al. (1999), Hornig et al. (1999), and Weissenböck et al. (2000); and alterations in cytokine gene expression have been reported by Hornig et al. (1999), Plata-Salaman et al. (1999) and Sauder et al. (1999).

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.

Borna disease virus

Borna disease virus (BDV) is unique amongst animal RNA viruses in its molecular biology and capacity to cause persistent, noncytolytic CNS-infection in a wide variety of host species. Unlike other non-segmented negative-strand RNA animal viruses, BDV replicates in the nucleus of the host cell where splicing is employed for expression of a very compact genome. Epidemiological studies indicate a broad host range and geographical distribution, and some investigators have proposed that human infection may result in neuropsychiatric disorders. Experimental Borna disease in neonatal and adult rats provides an intriguing model for immune-mediated disturbances of brain development and function.

CC chemokine receptor 2 is critical for induction of experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is a CD4(+) T lymphocyte-mediated disease of the central nervous system (CNS) characterized by mononuclear cell infiltration, demyelination, and paralysis. We previously demonstrated a role for chemokines in acute and relapsing EAE pathogenesis. Presently, we investigated the role of CC chemokine receptor 2 (CCR2) in acute EAE. CCR2(-/-) mice did not develop clinical EAE or CNS histopathology, and showed a significant reduction in T cell- and CNS-infiltrating CD45(high)F4/80(+) monocyte subpopulations. Peripheral lymphocytes from CCR2(-/-) mice produced comparable levels of interferon-gamma (IFN-gamma) and interleukin (IL)-2 in response to antigen-specific restimulation when compared with control mice. Adoptively transferred myelin oligodendrocyte glycoprotein 35-55-specific T cells lacking expression of CCR2 were able to induce EAE, whereas CCR2(-/-) recipients of wild-type T cells failed to develop disease. These results suggest that CCR2 expression on host-derived mononuclear cells is critical for disease induction.

CD28 costimulatory blockade exacerbates disease severity and accelerates epitope spreading in a virus-induced autoimmune disease

Theiler's murine encephalomyelitis virus (TMEV) is a natural mouse pathogen which causes a lifelong persistent infection of the central nervous system (CNS) accompanied by T-cell-mediated myelin destruction leading to chronic, progressive hind limb paralysis. TMEV-induced demyelinating disease (TMEV-IDD) is considered to be a highly relevant animal model for the human autoimmune disease multiple sclerosis (MS), which is thought to be initiated as a secondary consequence of a virus infection. Although TMEV-IDD is initiated by virus-specific CD4(+) T cells targeting CNS-persistent virus, CD4(+) T-cell responses against self myelin protein epitopes activated via epitope spreading contribute to chronic disease pathogenesis. We thus examined the ability of antibodies directed against B7 costimulatory molecules to regulate this chronic virus-induced immunopathologic process. Contrary to previous studies showing that blockade of B7-CD28 costimulatory interactions inhibit the initiation of experimental autoimmune encephalomyelitis, treatment of SJL mice at the time of TMEV infection with murine CTLA-4 immunoglobulin or a combination of anti-B7-1 and anti-B7-2 antibodies significantly enhanced clinical disease severity. Costimulatory blockade inhibited early TMEV-specific T-cell and antibody responses critical in clearing peripheral virus infection. The inhibition of virus-specific immune responses led to significantly increased CNS viral titers resulting in increased damage to myelin-producing oligodendrocytes. Following clearance of the costimulatory antagonists, epitope spreading to myelin epitopes was accelerated as a result of the increased availability of myelin epitopes leading to a more severe chronic disease course. Our results raise concern about the potential use of B7-CD28 costimulatory blockade to treat human autoimmune diseases potentially associated with acute or persistent virus infections.

The stimulation of low-affinity, nontolerized clones by heteroclitic antigen analogues causes the breaking of tolerance established to an immunodominant T cell epitope

H-2K mice injected, intravenously in saline or intraperitoneally in incomplete Freund's adjuvant, with large quantities of the immunodominant I-E(k)-restricted epitope from moth cytochrome c (MCC) 88-103 fail to respond to subsequent immunization with this epitope when administered in complete Freund's adjuvant. This state of tolerance can be broken by immunization with certain MCC 88-103 analogues that are heteroclitic antigens as assessed on representative MCC 88-103 specific T cell clones. In this paper, the mechanism of breaking tolerance by heteroclitic antigens was investigated. The following observations were made: (a) T cell hybridomas derived from tolerance-broken animals required higher concentrations of MCC 88-103 to be stimulated than hybridomas derived from normal immune animals, suggesting that they have T cell receptors (TCRs) of lower affinity; (b) in contrast to normal immune animals whose MCC-specific TCRs are typically Vbeta3(+)/Valpha11(+), none of the hybridomas derived from tolerance-broken animals expressed Vbeta3, although they were all Valpha11(+). Also, the Vbeta complementarity determining region 3 (CDR3) regions from the tolerance-broken animals did not contain the canonical structure and length characteristics of the normal MCC 88-103 immune repertoire; and (c) adoptive transfer and tolerization of MCC-specific Vbeta3(+)/Valpha11(+) transgenic T cells followed by immunization with heteroclitic antigen failed to terminate the state of tolerance. Collectively, these data strongly suggest that the mechanism involved in breaking tolerance in this system is the stimulation of nontolerized, low-affinity clones, rather than reversal of anergy. Further support for this mechanism was the finding that after activation, T cells apparently have a lowered threshold with respect to the affinity of interaction with antigen required for stimulation.

What is the role of regulatory T cells in transplantation tolerance?

There has been considerable recent progress in the characterization of the regulatory T cells that mediate tolerance in a number of transplantation models. The conditions that facilitate the generation of regulatory T cells point to the thymus, the nature of immune suppression and the dose of immunosuppressive agent(s) being important. Putative mechanisms of immune regulation by regulatory T cells, particularly in the 'infectious' tolerance pathway, include Th2-type cytokines (IL-4, IL-10 and transforming growth factor beta) that may play a direct role as an indispensable requirement or may contribute indirectly as a favorable milieu for acquisition of tolerance. Anergic T cells may suppress immune responses via either cytokine competition or antigen-presenting cells. Models of autoimmune disease, in which regulatory T cells were shown to represent a distinct thymus-derived T cell subset, also suggest the role of antigen-presenting cells in mediating immune suppression. Progress has also been made in generating and characterizing regulatory T cells in vitro.

Chemokine Regulation of Immune-mediated Demyelinating Disease

Experimental autoimmune encephalomyelitis (EAE) is a CD4+ Th1-mediated demyelinating disease of the central nervous system (CNS), which serves as a model for multiple schlerosis (MS). A hallmark in the pathogenesis of this disease is the emigration of T cells and monocytes from the blood to the CNS. Chemokines are small-molecular-weight chemotactic peptides, which are ligands for seven transmembrane-spanning, G protein-coupled receptors and which deliver signals leading to a variety of T cell functions including costimulation, cytokine expression, differentiation, and integrin activation. Several considerations suggest a role for chemokines in the influx of inflammatory cells to the CNS and the resulting disease process, including a tight temporal expression pattern with a relation to disease activity and prevention of disease development by in vivo neutralization. This article reviews the evidence that temporal and spatial expressions of chemokines are critical factors that regulate EAE, which makes this an appropriate animal model to study the pathogenesis of MS disease activity.

Diverse Fine Specificity and Receptor Repertoire of T Cells Reactive to the Major VP1 Epitope (VP1230–250) of Theiler’s Virus: Vβ Restriction Correlates with T Cell Recognition of the C-Terminal Residue

Theiler’s murine encephalomyelitis virus induces chronic demyelinating disease in genetically susceptible mice. The histopathological and immunological manifestation of the disease closely resembles human multiple sclerosis, and, thus, this system serves as a relevant infectious model for multiple sclerosis. The pathogenesis of demyelination appears to be mediated by the inflammatory Th1 response to viral epitopes. In this study, T cell repertoire reactive to the major pathogenic VP1 epitope region (VP1233–250) was analyzed. Diverse minimal T cell epitopes were found within this region, and yet close to 50% of the VP1-reactive T cell hybridomas used Vβ16. The majority (8/11) of the Vβ16+ T cells required the C-terminal amino acid residue on the epitope, valine at position 245, and every T cell hybridoma recognizing this C-terminal residue expressed Vβ16. However, the complementarity-determining region 3 sequences of the Vβ16+ T cell hybridomas were markedly heterogeneous. In contrast, such a restriction was not found in the Vα usage. Only restricted residues at this C-terminal position allowed for T cell activation, suggesting that Vβ16 may recognize this terminal residue. Further functional competition analysis for TCR and MHC class II-contacting residues indicate that many different residues can be involved in the class II and/or TCR binding depending on the T cell population, even if they recognize the identical minimal epitope region. Thus, recognition of the C-terminal residue of a minimal T cell epitope may associate with a particular Vβ (but not Vα) subfamily-specific sequence, resulting in a highly restricted Vβ repertoire of the epitope-specific T cells.

Dose-Dependent Induction of Distinct Anergic Phenotypes: Multiple Levels of T Cell Anergy

T cell anergy has been proposed as one of the mechanisms underlying peripheral T cell tolerance. In recent years, the functional relevance of T cell anergy has been studied extensively in vitro and in vivo, using different species, cell systems, and ways to induce anergy. Although these studies concurred about the induction of unresponsiveness, conflicting findings were obtained with respect to the function of anergic T cells and to the persistence of T cell anergy. In the present study, T cell anergy was induced through T-T presentation of the specific Ag by rat MHC class II+ T cells in the absence of professional APC. We show that, depending on the Ag dose with which T cells were incubated, distinct anergic phenotypes were induced. Incubation of T cell clones with a low (suboptimal) Ag dose induced hyporesponsiveness. Incubation with a higher (optimal) Ag dose induced an anergic state capable of exerting immunoregulatory effects. Incubation with a high (supraoptimal) Ag dose led to an anergic suppressive phenotype that was persistent and was not reversed by APC, Ag, and rIL-2. These findings demonstrate that T cell anergy is not confined to a single state of functional inactivation. Instead, multiple levels of T cell anergy exist. Thus, anergic T cells can contribute to the regulation of the immune response either in a persistent and active manner or in a passive manner, depending on their level of T cell anergy.

Acute and relapsing experimental autoimmune encephalomyelitis are regulated by differential expression of the CC chemokines macrophage inflammatory protein-1alpha and monocyte chemotactic protein-1

Experimental autoimmune encephalomyelitis (EAE) is a T lymphocyte-mediated disease of the central nervous system (CNS), characterized by mononuclear cell infiltration and demyelination resulting in paralysis. We examined CC chemokine expression in the CNS throughout the entire course of the disease and found that the production of macrophage inflammatory protein (MIP)-1alpha correlated with increasing acute disease severity and remained elevated throughout chronic, relapsing disease. In contrast, a substantial level of monocyte chemotactic protein (MCP)-1 expression was not observed until late in acute disease and continued to be evident in the relapsing phase of the disease. MCP-1 expression correlated with increasing severity of clinical relapses. Lower levels of RANTES in the CNS were noted throughout the disease course, but showed little correlation with either acute or relapsing disease. Although RANTES expression was observed during the entire course of disease, anti-RANTES treatment had no effect on clinical disease progression. Anti-MCP-1, but not anti-MIP-1alpha, treatment during relapsing EAE decreased clinical severity of relapsing disease. Furthermore, anti-MCP-1 treatment reduced CNS macrophage accumulation during relapsing EAE. These results suggest that MIP-1alpha controls mononuclear cell accumulation during acute EAE, while MCP-1 controls mononuclear cell infiltration during relapsing EAE.

Characterization of and functional antigen presentation by central nervous system mononuclear cells from mice infected with Theiler's murine encephalomyelitis virus

We examined the phenotype and function of cells infiltrating the central nervous system (CNS) of mice persistently infected with Theiler's murine encephalomyelitis virus (TMEV) for evidence that viral antigens are presented to T cells within the CNS. Expression of major histocompatibility complex (MHC) class II in the spinal cords of mice infected with TMEV was found predominantly on macrophages in demyelinating lesions. The distribution of I-As staining overlapped that of the macrophage marker sialoadhesin in frozen sections and coincided with that of another macrophage/microglial cell marker, F4/80, by flow cytometry. In contrast, astrocytes, identified by staining with glial fibrillary acidic protein, rarely expressed detectable MHC class II, although fibrillary gliosis associated with the CNS damage was clearly seen. The costimulatory molecules B7-1 and B7-2 were expressed on the surface of most MHC class II-positive cells in the CNS, at levels exceeding those found in the spleens of the infected mice. Immunohistochemistry revealed that B7-1 and B7-2 colocalized on large F4/80(+) macrophages/microglia in the spinal cord lesions. In contrast, CD4(+) T cells in the lesions expressed mainly B7-2, which was found primarily on blastoid CD4(+) T cells located toward the periphery of the lesions. Most interestingly, plastic-adherent cells freshly isolated from the spinal cords of TMEV-infected mice were able to process and present TMEV and horse myoglobin to antigen-specific T-cell lines. Furthermore, these cells were able to activate a TMEV epitope-specific T-cell line in the absence of added antigen, providing conclusive evidence for the endogenous processing and presentation of virus epitopes within the CNS of persistently infected SJL/J mice.

Anergic T cells actively suppress T cell responses via the antigen-presenting cell

We here show that anergic T cells are active mediators of T cell suppression. In co-culture experiments, we found that anergic T cells, derived from established rat T cell clones and rendered anergic via T cell presentation of the specific antigen (Ag), were active inhibitors of T cell responses. Anergic T cells inhibited not only the responses of T cells with the same Ag specificity as the anergic T cells, but were also capable of efficiently inhibiting polyclonal T cell responses directed to other epitopes. This suppression required close cell-cell contact between antigen-presenting cells (APC), anergic T cells and responder T cells, and only occurred when the epitope recognized by the anergic T cell was present. The suppression was not caused by passive competition for ligands on the APC surface, IL-2 consumption, or cytolysis, and was not mediated by soluble factors derived from anergic T cells that were stimulated with their specific Ag. When responder T cells were added 24 h after co-culturing anergic cells in the presence of Ag and APC, T cell responses were still suppressed, indicating that the suppressive effect was persistently present. However, anergic T cells were not able to suppress responder T cells that had already received a full activation signal. We propose that suppression by anergic T cells is mediated via the APC, either through modulation of the T cell-activating capacity of the APC (APC/T cell interaction), or by inhibition of T cells recognizing their ligand in close proximity on the same APC (T/T cell interaction).

Peripheral Immune Tolerance Blocks Clonal Expansion but Fails to Prevent the Differentiation of Th1 Cells

Clonal anergy in Ag-specific CD4+ T cells is shown in these experiments to inhibit IL-2 production and clonal expansion in vivo. We also demonstrate that the defect in IL-2 gene inducibility can be achieved in both naive and Th1-like memory T cells when repeatedly exposed to aqueous peptide Ag. Nevertheless, this induction of clonal anergy did not interfere with the capacity of naive T cells to differentiate into Th1-like effector cells, nor did it prevent such helper cells from participating in T-dependent IgG2a anti-hapten responses and delayed-type hypersensitivity reactions. Thus, clonal anergy can contribute to the development of Ag-specific immune tolerance by limiting the size of a Th cell population, but not by disrupting its effector function.

A Synthetic CD4-CDR3 Peptide Analog Enhances Skin Allograft Survival Across a MHC Class II Barrier

The efficacy of a synthetic peptide analogue (rD-mPGPtide), mimicking the CDR3 region in the first domain of the CD4 surface molecule, was investigated in a murine model for CD4+ T cell-mediated skin allograft rejection. A single injection of rD-mPGPtide shortly before transplantation exhibited significantly prolonged graft survival in the B6 anti-B6.C-H2bm12 MHC class II-disparate strain combination. Long-term graft survival (>100 days) was achieved when thymectomized adult recipient mice were transplanted along with rD-mPGPtide treatment. The peptide also affected secondary rechallenge responses with MHC class II allografts. In addition, the inhibitory effect of the rD-mPGPtide in this transplantation model was directed against CD4+ T cells and was exclusively specific toward donor alloantigen. In vitro analysis of CD4+ T cells isolated from the draining lymph nodes of rD-mPGPtide-treated recipients indicated a 450-fold decrease in precursor frequency in response to donor allostimulation compared with the untreated control group. There was also significant down-regulation of the frequency of IL-2-, IFN-γ-, and IL-4-producing CD4+ T cells upon in vitro allogeneic restimulation of host cells 4 days posttransplantation. However, these same CD4+ T cells maintained the capacity to produce normal cytokine levels upon third-party allostimulation. Thus, these studies demonstrate that a CD4-CDR3 peptide analogue can specifically and effectively prolong skin graft survival across MHC class II barriers.

Th1 unresponsiveness can be infectious for unrelated antigens

CD4+ T cells may be assigned a functional status (Th1 or Th2) according to the cytokines they produce including IL-2, IFN-gamma and IL-4. Th1 and Th2 CD4+ T cells deliver different isotype-switching signals to antigen-specific B cells which bias the serum Ig isotypes. The stimulation of Th1 or Th2 responses is influenced by adjuvants and administration of antigen in IFA results in Th1 unresponsiveness as evidenced by: (i) reduced T cell proliferation to antigen; (ii) reduced IFN-gamma production in response to antigen; and (iii) reduced IgG2a isotype antigen-specific antibodies following antigen/CFA challenge. The impact of established human gamma globulin (HGG) specific Th1 unresponsiveness on subsequent immunization with an unrelated antigen, human serum albumin (HSA) in Th1-inducing CFA was then examined. When subsequently challenged with a mixture of HSA and HGG in CFA the HGG-specific Th1 unresponsiveness was infectious and dominant, preventing the induction of a Th1 response to HSA. Reduced T cell proliferation, IFN-gamma production and IgG2a antibody were consequently observed in response to HSA. The HGG-specific Th1 unresponsiveness was not infectious when HGG/CFA and HSA/CFA were administered at separate sites. This demonstrates that antigen-specific Th1 unresponsiveness can be infectious for new, molecularly unrelated antigens and supports studies showing that Th1-mediated autoimmune diseases such as experimental allergic encephalomyelitis (EAE) and diabetes can be ameliorated using antigens molecularly distinct from the disease-inducing immunogen.

Regulation of the effector stages of experimental autoimmune encephalomyelitis via neuroantigen-specific tolerance induction. III. A role for anergy/deletion

Our previous work has shown that specific peripheral immune tolerance induced by the intravenous administration of ECDI-fixed, antigen-coupled syngeneic splenocytes is an extremely efficient method for prevention and treatment of chronic relapsing experimental autoimmune encephalomyelitis (R-EAE) in susceptible SJL/J mice. The current study examined the mechanisms by which unresponsiveness is induced in primed encephalitogenic T cells. The results indicate that the inhibition of MBP-specific T cells by the i.v. injection of MBP-coupled splenocytes is not due to the induction of antigen-specific regulatory T cells, but rather to the induction of anergy/deletion of the effector cells. This conclusion is supported by the findings that spleen or lymph node cells isolated from MBP-tolerant mice fail to inhibit the adoptive transfer of R-EAE in cotransfer assays, and that tolerance is not inhibited by prior thymectomy or prior treatment with cyclophosphamide or anti-CD8 monoclonal antibody. In contrast, we demonstrate that splenocytes from MBP-tolerized, asymptomatic mice have a significantly reduced ability to serially transfer R-EAE to naive secondary recipients following antigen re-activation in vitro, in the first several weeks following tolerization, but that the ability to serially transfer R-EAE returns to sham tolerant control levels within 1-2 months. We also demonstrate a significantly reduced precursor frequency of MBP-specific, IL-2-producing T cells in the MBP-tolerant within three days of treatment. Collectively, the data most closely support a model wherein inhibition of MBP-specific encephalitogenic CD4+ effector T cells by i.v. injected MBP-coupled splenocytes is due to the direct induction of anergy/deletion from which they can recover over time.

Mechanisms of recovery from experimental autoimmune encephalomyelitis: T cell deletion and immune deviation in myelin basic protein T cell receptor transgenic mice

Experimental autoimmune encephalomyelitis (EAE) is a Th1-type cell-mediated autoimmune disease directed against central nervous system (CNS) myelin antigens such as myelin basic protein (MBP). EaE is usually characterized by spontaneous remission of clinical disease and immune pathology despite the persistence of self myelin antigens in the central nervous system. Following induction of an acute episode of EAE, spontaneous remission also occurs in MBP T cell receptor (TCR) transgenic mice even through most T cells express a TCT specific for MBP. To investigate the mechanisms of recovery associated with EAE, we examined the behavior of MBP-specific T cells in the MBP TCR transgenic mouse model during disease progression and recovery. We found that recovery from EAE was associated with three major immunologic changes: (1) deletion of encephalitogenic T cells in the brain; (2) deviation of MBP-specific transgenic (Tg+) T cells both in the periphery and in the central nervous system from INF- gamma secretin Th1 type cells to cells that secrete IL-4, IL-10, and TGF- beta ; and (3) deletion of Tg+ T cells in the thymus through apoptosis. Thus spontaneous recovery from a classic Th1 type organ specific autoimmune disease is associated with two mechanisms of immune tolerance, deletion of autoreactive cells and immune deviation of autoreactive cells to a non-pathogenic phenotype.

A spontaneous low-pathogenic variant of Theiler's virus contains an amino acid substitution within the predominant VP1(233-250) T-cell epitope

Theiler's murine encephalomyelitis virus (TMEV) induces immune-mediated demyelination after intracerebral inoculation of the virus into susceptible mouse strains. We isolated from a TMEV BeAn 8386 viral stock, a low-pathogenic variant which requires greater than a 10,000-fold increase in viral inoculation for the manifestation of detectable clinical signs. Intracerebral inoculation of this variant virus induced a strong, long-lasting, protective immunity from the demyelinating disease caused by pathogenic TMEV. The levels of antibodies to the whole virus as well as to the major linear epitopes were similar in mice infected with either the variant or wild-type virus. However, persistence of the variant virus in the central nervous system (CNS) of mice was significantly lower than that of the pathogenic virus. In addition, the T-cell response to the predominant VP1 (VP1(233-250)) epitope in mice infected with the variant virus was significantly weaker than that in mice infected with the parent virus, while similar T-cell responses were induced against another predominant epitope (VP2(74-86)). Further analyses indicated that a change of lysine to arginine at position 244 of VP1, which is the only amino acid difference in the P1 region, is responsible for such differential T-cell recognition. Thus, the difference in the T-cell reactivity to this VP1 region as well as the low level of viral persistence in the CNS may account for the low pathogenicity of this spontaneous variant virus.

Nasal administration of myelin basic protein prevents relapsing experimental autoimmune encephalomyelitis in DA rats by activating regulatory cells expressing IL-4 and TGF-beta mRNA

This study explores nasal administration of myelin basic protein (MBP) as a potential means of inducing tolerance to relapsing experimental autoimmune encephalomyelitis (PR-EAE), an experimental multiple sclerosis (MS) model that was induced in DA rats by immunization with rat spinal cord homogenate and incomplete Freund's adjuvant. DA rats received a total dosage of 0, 6, 60, 600 micrograms/rat of bovine MBP on ten consecutive days prior to immunization. EAE with typical course was observed in control rats receiving only PBS nasally, and in rats receiving 6 micrograms/rat of MBP. Rats receiving 60 micrograms/rat of MBP developed acute EAE but no relapse during 60 days of observation post immunization (p.i.). Only one of eight rats receiving 600 micrograms/rat of MBP developed slight, transient EAE. This protection was confirmed at the histology level and was associated with decreased levels of MBP-reactive IFN-gamma secreting Th1-like spleen cells on day 13 and 60 p.i. Rats receiving 60 and 600 micrograms/rat of MBP showed decreased serum anti-MBP IgG2b antibody levels on day 60 p.i., and rats receiving 600 micrograms/rat of MBP had marginally increased anti-MBP IgG1 antibody levels in serum compared to control EAE rats. Cytokine mRNA profiles in central nervous system (CNS) and spleen mononuclear cells were evaluated. Dose-dependent reduction of TNF-alpha mRNA expression were observed both in CNS and in splenocytes. Increased IL-4 and TGF-beta mRNA expression were observed in CNS of low (6 micrograms/rat) and median (60 micrograms/rat) dose of MBP tolerized rats and in splenocytes of rats tolerized with 600 micrograms/rat of MBP. We conclude that nasal administration of MBP in DA rat prevents EAE induced by immunization with whole rat spinal cord homogenate that, besides MBP, contains multiple antigenic myelin proteins. A mechanism involving MBP-reactive regulatory cells expressing IL-4 and TGF-beta mRNA acts as part in the induction of this tolerance.

The infection of mouse by Theiler's virus: from genetics to immunology

Theiler's virus is a picornavirus of mouse which causes an acute encephalomyelitis followed by a persistent infection of the white matter of the spinal cord with chronic inflammation and demyelination. This late disease is studied as a model for multiple sclerosis. Inbred strains of mice differ in their susceptibility to persistent infection and demyelination. Resistant strains clear the infection after the acute encephalomyelitis. This observation is the basis of genetic studies which we used as a thread for this review. The H-2D locus has a major effect on susceptibility. The H-2Db gene is involved in a fast and intense CTL response which confers resistance. The Tcrb locus is also implicated, although there is no proof that the susceptibility gene in this region codes for the T-cell receptor. A complete screen of the genome uncovered the role of the Ifng locus and led to the demonstration that IFN-gamma limits viral spread in the white matter. The roles of NK cells and B cells in limiting the infection are discussed. CD4+ T cells participate both in protection against the infection and in demyelination. Finally, the effect of non-immune factors in resistance is illustrated by mice with mutations in the MBP or PLP gene.

Central nervous system cytokine mRNA expression following Theiler's murine encephalomyelitis virus infection

DA strain of Theiler's murine encephalomyelitis virus (TMEV) produces a biphasic disease with an initial self-limited acute gray matter polioencephalomyelitis in all strains of mice followed by, in the case of certain susceptible strains of mice, a chronic inflammatory demyelination of the spinal cord with a persistent virus infection. A pathogenic role for T-helper 1 (Th1) cells during the demyelinating phase of disease has been proposed. We characterized the cytokine mRNA expression in the brain and spinal cord of susceptible and resistant strains of mice during the early encephalomyelitic disease and the late demyelination, using a semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) assay. At the time of the encephalomyelitis, both resistant and susceptible mice expressed proinflammatory cytokine mRNAs followed by T-cell derived mRNAs; susceptible mice expressed more IL-12 p40 mRNA than resistant mice. During this early disease, there was no significant difference in Th1 cytokine mRNA expression in the brain and spinal cord among the four strains and relatively little Th2 type cytokine upregulation above levels seen in mock-infected controls. During the late demyelinating disease, susceptible but not resistant mice had evidence of viral genome and a continuous expression of Th1 type cytokine mRNAs. The expression of Th2 cytokine mRNAs varied among the different strains and did not correlate with susceptibility or resistance. The results indicate the complexity of cytokine mRNA expression following TMEV infection and the dependence of the expression on disease pathology, the time following infection and the genetics of the host.