Interstrain variability of autoimmune encephalomyelitis in rats: multiple encephalitogenic myelin basic protein epitopes for DA rats

Animal Models of Multiple Sclerosis

Animal models with high translational validity are essential tools in understanding disease pathogenesis and in the development of therapeutic strategies. Multiple sclerosis (MS) is an autoimmune demyelinating disease of the central nervous system characterized by progressive neurological deficits and socioeconomic burden. Experimental autoimmune encephalomyelitis (EAE) is the most extensively utilized animal model of MS, with well-characterized rodent and non-human primate variants. The EAE model is typically induced by either active immunization with myelin-derived proteins or peptides in adjuvant or by passive transfer of activated myelin-specific CD4⁺ T lymphocytes. To date, the EAE model has been an essential tool in the development of at least seven U.S. Food and Drug Administration (FDA)-approved immunomodulatory drugs for the treatment of MS, including glatiramer acetate, fingolimod, and natalizumab. However, the translational validity of the EAE model is frequently compromised due to poor study design, inconsistent clinical scoring endpoints, and inappropriate statistical calculations. No single animal model accurately reflects the complexity of human MS pathogenesis. Beyond EAE, multiple additional animal models are described, including Theiler's murine encephalomyelitis virus and cuprizone-induced demyelination, which facilitate the study of pathogen-induced CNS autoimmunity and remyelination, respectively. This overview summarizes several of the most frequently used animal models of MS and highlights key factors that significantly influence the experimental outcome and affect translational validity. © 2021 Wiley Periodicals LLC.

Animal models of multiple sclerosis: Focus on experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is a chronic, progressive disorder of the central nervous system (CNS) that affects more than two million people worldwide. Several animal models resemble MS pathology; the most employed are experimental autoimmune encephalomyelitis (EAE) and toxin- and/or virus-induced demyelination. In this review we will summarize our knowledge on the utility of different animal models in MS research. Although animal models cannot replicate the complexity and heterogeneity of the MS pathology, they have proved to be useful for the development of several drugs approved for treatment of MS patients. This review focuses on EAE because it represents both clinical and pathological features of MS. During the past decades, EAE has been effective in illuminating various pathological processes that occur during MS, including inflammation, CNS penetration, demyelination, axonopathy, and neuron loss mediated by immune cells.

Promiscuity of autoimmune responses to MBP after stroke

In this study we examined Th1 and Th17 immune responses to rat myelin basic protein (MBP), bovine MBP, human MBP, MBP 68-86, MBP 63-81 and ovalbumin in Lewis rats to determine which MBP antigen is recognized following ischemic brain injury. Responses were compared to animals immunized to rat MBP. Data show that immune responses following immunization with rat MBP are promiscuous with cross reaction to MBP from other species. After stroke, few animals develop Th1 or Th17 responses to MBP, but when those responses occur, especially Th1 responses to rat MBP in the brain, they are predictive of worse stroke outcome.

Experimental autoimmune encephalomyelitis in the rat

There are several diverse rat models of experimental autoimmune encephalomyelitis (EAE) that can be used to investigate the pathogenesis and regulation of autoimmunity against CNS myelin. The disease course of these models ranges from an acute monophasic disease with limited demyelination to a chronic relapsing or chronic progressive course marked by severe demyelination. These models enable the study of encephalitogenic T cells and demyelinating antibody specific for major neuroantigens such as myelin basic protein (MBP), myelin oligodendrocyte glycoprotein (MOG), or proteolipid protein (PLP), among other important CNS autoantigens. Overall, this unit provides an overview of common methods for induction of active and passive EAE, assessment and analysis of clinical disease, preparation and purification of myelin basic protein, and derivation of neuroantigen-specific rat T cell lines. This unit also provides a brief discussion of the basic characteristics of these models.

Induction of experimental autoimmune encephalomyelitis in Dark Agouti rats without adjuvant

Experimental autoimmune encephalomyelitis (EAE) is a well-recognized model for multiple sclerosis (MS) in humans. However, adjuvants used with encephalitogens to induce EAE produce non-specific effects interfering with the mechanisms involved in the autoimmune response to the central nervous system (CNS) tissue. It is therefore important to establish a more suitable model of EAE for analysis of autoimmune phenomena resembling those operative in MS. Here we report that EAE can be induced regularly in Dark Agouti (DA) strain of rats with spinal cord tissue without any adjuvant, as judged by both clinical and histological parameters. The incidence and severity of EAE depended on the origin of the encephalitogen, the rat versus guinea pig spinal cord homogenate being more efficient. Furthermore, EAE could be reinduced in animals which had recovered from disease that had been induced actively with encephalitogen alone, suggesting the role of adjuvant-generated non-specific mechanisms in resistance to reinduction of EAE. Thus, EAE induced in DA rats with encephalitogen alone provides a reproducible model for defining pathogenically relevant events in CNS autoimmunity devoid of the potentially misleading effects of adjuvants.

Characterization of the antigen specificity and TCR repertoire, and TCR-based DNA vaccine therapy in myelin basic protein-induced autoimmune encephalomyelitis in DA rats

Like Lewis rats, DA rats are an experimental autoimmune encephalomyelitis (EAE)-susceptible strain and develop severe EAE upon immunization with myelin basic protein (MBP). However, there are several differences between the two strains. In the present study we induced acute EAE in DA rats by immunization with MBP and MBP peptides and examined the Ag specificity and TCR repertoire of encephalitogenic T cells. It was found that although immunization with MBP and a peptide corresponding to its 62-75 sequence (MBP(62-75)) induced clinical EAE, the responses of lymph node T cells isolated from MBP-immunized rats to MBP(62-75) was marginal, indicating that this peptide contains major encephalitogenic, but not immunodominant, epitopes. The TCR analysis by CDR3 spectratyping of spinal cord T cells revealed that Vbeta10 and Vbeta15 spectratype expansion was always found in MBP(62-75)-immunized symptomatic rats. On the basis of these findings, we examined the encephalitogenicity of Vbeta10- and Vbeta15-positive T cells. First, the adoptive transfer experiments revealed that Vbeta10-positive T line cells derived from MBP(62-75)-immunized rats induced clinical EAE in recipients. Second, administration of DNA vaccines encoding Vbeta10 and Vbeta15, alone or in combination, ameliorated MBP(62-75)-induced EAE. Collectively, it was strongly suggested that Vbeta10- and Vbeta15-positive T cells are encephalitogenic. Analyses of the Ag specificity and T cell repertoire of pathogenic T cells performed in this study provide useful information for designing specific immunotherapies against autoimmune diseases.

Importance of cryptic myelin basic protein epitopes in the pathogenicity of acute and recurrent anterior uveitis associated with EAE

Lewis rats immunized with myelin basic protein (MBP) develop experimental autoimmune encephalomyelitis (EAE) and associated anterior uveitis (AU), which can relapse without recurring of EAE. In this study, we analyzed the repertoire of MBP epitopes that play a role in acute and recurrent AU by injection of MBP synthetic peptides. In addition to the encephalitogenic epitopes 69-89 and 87-99, several cryptic epitopes were found to be strongly uveitogenic in Lewis rats upon immunization with synthetic peptides, including 100-120, 121-140 and 142-167. However, the peptide corresponding to the MBP residues 1-20 was uniquely capable of inducing AU without EAE. Immunization with intact MBP was not essential for the induction of the recurrence of AU. The responses of T cells from lymph nodes and spleens showed a dominant response to the original disease-induced epitope with responses to secondary epitopes. In conclusion, the analysis of pathogenic determinants important for the induction of uveitis provides further evidence that MBP-specific T cells also contribute to the pathogenesis of anterior uveitis. Moreover, this also suggests that a distinct immunoregulatory mechanism exists in the eye and spinal cord because of the uniqueness of the epitope 1-20 in AU but not EAE, and the capability of MBP-specific T cells of inducing AU without EAE.

Characterization of acute versus chronic relapsing autoimmune encephalomyelitis in DA rats

This study was undertaken to better understand the role of cytokines in the pathogenesis, especially in the mechanisms of relapse, of experimental autoimmune encephalomyelitis (EAE). For this purpose, we induced acute and chronic relapsing (CR) EAE in DA rats and determined several immunological parameters in rats at various stages of two types of EAE. Histopathological analysis revealed that there was no significant difference in the severity of inflammation in the spinal cord lesions between the two groups. However, demyelination was observed only in rats with CR EAE. Cytokine analysis by competitive PCR demonstrated that levels of TNF-alpha, IL-6 and IL-12 p40 mRNA in the spinal cord at the first attack of CR EAE were significantly higher than those at the peak stage of acute EAE. The mRNA expression of anti-inflammatory cytokines, IL-10 and TGF-beta1, was generally low in both acute EAE and the first attack of CR EAE and upregulated at later stages of CR EAE. These findings suggest that persistent high-level expression of pro-inflammatory cytokines is closely associated with demyelination and relapse of EAE. In contrast, anti-inflammatory cytokines play only a minor role in the relapse.

Increasing the frequency of T-cell precursors specific for a cryptic epitope of hen-egg lysozyme converts it to an immunodominant epitope

Efforts to understand the mechanisms that govern how immunodominant T-cell epitopes are selected from protein antigens have focused mostly on differences in the efficiency of processing and presentation of peptide/major histocompatibility complex (MHC) complexes by antigen-presenting cells, while little attention has been directed at the role of the T-cell repertoire. In this report, the influence of the T-cell repertoire on immunodominance was investigated using transgenic mice that express the beta chain from a T-cell receptor specific for a cryptic Ek restricted epitope of hen-egg lysozyme, HEL85-96. In these mice, the frequency of HEL85-96-specific T-cell precursors is increased 10-20-fold over non-transgenic mice. Transgenic mice respond as well as non-transgenic controls to intact HEL, even though they respond poorly or not at all to a variety of other antigens, including the dominant H-2k restricted epitopes of HEL. Following immunization with native HEL, the only HEL peptide that could recall a response in vitro in the transgenic mice was HEL85-96. Therefore, this normally cryptic epitope is the sole immunodominant epitope in the transgenic mice, and this alteration in immune response is due solely to an increase in the frequency of specific T-cell precursors. An analysis of four additional H-2k restricted cryptic epitopes of HEL suggests that three are similarly limited by T-cell frequency, and that only one is consistent with a defect in efficient antigen presentation. This indicates that there are at least two different types of cryptic epitopes, one in which crypticity is caused by inefficient processing or presentation, and another in which the frequency of specific T-cell progenitors is limiting.

Allelic variations in rat MHC class II binding of myelin basic protein peptides correlate with encephalitogenicity

The impact of the strength and promiscuity of the self peptide-MHC class II interaction on susceptibility to autoimmune disease is uncertain. Here we studied allelic differences in the affinity of rat MHC class II molecules for myelin basic protein (MBP) peptides spanning from position 63 to 106. Predominantly peptides from this region are immunogenic in the rat and the MHC class II region determines if the response is disease promoting or disease protective. Strikingly, RT1.B (DQ-like) molecules showed much more allelic variation of MBP peptide binding than RT1.D (DR-like) molecules. Moderate to strong binding of particular MBP peptides correlated with their previously documented encephalitogenicity. Moreover, the differences in disease susceptibility to certain MBP peptides observed in the different rat strains were clearly reflected in the allelic diversity of the peptide binding profiles. In conclusion our findings demonstrate that disease-inducing stretches of MBP generally comprise good binding peptides.

Delineation of two encephalitogenic myelin basic protein epitopes for DA rats

We studied synthetic peptides that correspond to two regions of the guinea pig myelin basic protein (MBP) molecule which elicit experimental autoimmune encephalomyelitis (EAE) in DA rats. Using truncated peptides, we determined that two encephalitogenic epitopes reside within MBP63-81, a major determinant defined by MBP residues, 63-76, and a minor encephalitogenic epitope defined by residues, 66-81. Experiments with alanine-substituted analogs of MBP63-76 revealed that the HYGSLP sequence is critical for encephalitogenicity. The core epitope within a second encephalitogenic region, MBP101-120, was defined by residues, 106-119. Studies with analogs of this sequence indicated that residues, Leu 111, Phe 114 and Trp 116 are important for T-cell responsiveness.