Multiple discrete encephalitogenic epitopes of the autoantigen myelin basic protein include a determinant for I-E class II-restricted T cells

Experimental Autoimmune Encephalomyelitis in the Mouse

This article details the materials and methods required for both active induction and adoptive transfer of experimental autoimmune encephalomyelitis (EAE) in the SJL mouse strain using intact proteins or peptides from the two major myelin proteins: proteolipid protein (PLP) and myelin basic protein (MBP). Additionally, active induction of EAE in the C57BL/6 strain using myelin oligodendrocyte glycoprotein (MOG) peptide is also discussed. Detailed materials and methods required for the purification of both PLP and MBP are described, and a protocol for isolating CNS-infiltrating lymphocytes in EAE mice is included. Modifications of the specified protocols may be necessary for efficient induction of active or adoptive EAE in other mouse strains. © 2021 Wiley Periodicals LLC. Basic Protocol: Active induction of EAE with PLP, MBP, and MOG protein or peptide Alternate Protocol: Adoptive induction of EAE with PLP-, MBP-, or MOG-specific lymphocytes Support Protocol 1: Purification of proteolipid protein Support Protocol 2: Purification of myelin basic protein Support Protocol 3: Isolation of CNS-infiltrating lymphocytes.

Experimental Autoimmune Encephalomyelitis in Mice

Experimental autoimmune encephalitis (EAE), the animal model of multiple sclerosis (MS), has provided significant insight into the mechanisms that initiate and drive autoimmunity. Several central nervous system proteins and peptides have been used to induce disease, in a number of different mouse strains, to model the diverse clinical presentations of MS. In this chapter, we detail the materials and methods used to induce active and adoptive EAE. We focus on disease induction in the SJL/J, C57BL/6, and BALB/c mouse strains, using peptides derived from proteolipid protein, myelin basic protein, and myelin oligodendrocyte glycoprotein. We also include a protocol for the isolation of leukocytes from the spinal cord and brain for flow cytometric analysis.

Inverse Vaccination to Silence Immunity to Myelin in Multiple Sclerosis

The adaptive immune response in multiple sclerosis is complex. We have devised large scale arrays to measure the antibody response to myelin proteins and lipids. Despite the widespread immune responses to myelin, we have devised an inverse vaccine aimed at turning off key drivers of this diverse response. Clinical trials in patients with multiple sclerosis show that it is possible to constrain antibody responses to myelin on a large scale with this approach.

Immunodominant T-cell epitopes of MOG reside in its transmembrane and cytoplasmic domains in EAE

Objective:

Studies evaluating T-cell recognition of myelin oligodendrocyte glycoprotein (MOG) in multiple sclerosis (MS) and its model, experimental autoimmune encephalomyelitis (EAE), have focused mostly on its 117 amino acid (aa) extracellular domain, especially peptide (p) 35-55. We characterized T-cell responses to the entire 218 aa MOG sequence, including its transmembrane and cytoplasmic domains.

Methods:

T-cell recognition in mice was examined using overlapping peptides and intact full-length mouse MOG. EAE was evaluated by peptide immunization and by adoptive transfer of MOG epitope-specific T cells. Frequency of epitope-specific T cells was examined by ELISPOT.

Results:

Three T-cell determinants of MOG were discovered in its transmembrane and cytoplasmic domains, p119–132, p181–195, and p186–200. Transmembrane MOG p119-132 induced clinical EAE, CNS inflammation, and demyelination as potently as p35-55 in C57BL/6 mice and other H-2^b strains. p119-128 contained its minimal encephalitogenic epitope. p119-132 did not cause disease in EAE-susceptible non-H-2^b strains, including Biozzi, NOD, and PL/J. MOG p119-132–specific T cells produced Th1 and Th17 cytokines and transferred EAE to wild-type recipient mice. After immunization with full-length MOG, a significantly higher frequency of MOG-reactive T cells responded to p119-132 than to p35-55, demonstrating that p119-132 is an immunodominant encephalitogenic epitope. MOG p181-195 did not cause EAE, and MOG p181-195–specific T cells could not transfer EAE into wild-type or highly susceptible T- and B-cell–deficient mice.

Conclusions:

Transmembrane and cytoplasmic domains of MOG contain immunodominant T-cell epitopes in EAE. A CNS autoantigen can also contain nonpathogenic stimulatory T-cell epitopes. Recognition that a myelin antigen contains multiple encephalitogenic and nonencephalitogenic determinants may have implications for therapeutic development in MS.

Experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is an inflammatory demyelinating disease of the central nervous system that is induced in laboratory animals by the generation of an immune response against myelin epitopes. It has been used as a prototype of Th1- and/or Th17-driven, organ-specific autoimmunity and as a model for the human disease, multiple sclerosis. In this chapter we describe two classic protocols for EAE induction (active immunization and adoptive transfer of Th1- or Th17-polarized cells) in Subheadings 3.1 and 3.2, respectively. Subheading 3.3 describes methods for rating clinical disease in symptomatic animals. Subheading 3.4 includes instructions for the isolation of mononuclear cells from the inflamed spinal cords of mice with EAE. Subheading 3.5 describes a method for performing the enzyme-linked immunospot assay.

Experimental autoimmune encephalomyelitis in the mouse

This unit details the materials and methods required for both active induction and adoptive transfer of experimental autoimmune encephalomyelitis (EAE) in the SJL mouse strain using intact proteins or peptides from the two major myelin proteins: proteolipid protein (PLP) and myelin basic protein (MBP). Detailed materials and methods required for the purification of both PLP and MBP are also described. A protocol for isolating CNS-infiltrating lymphocytes in EAE mice is included. Modifications of the specified protocols may be necessary for efficient induction of active or adoptive EAE in other mouse strains.

Immunological basis for the development of tissue inflammation and organ-specific autoimmunity in animal models of multiple sclerosis

Experimental autoimmune encephalomyelitis (EAE) is an animal model for multiple sclerosis (MS) that has shaped our understanding of autoimmune tissue inflammation in the central nervous system (CNS). Major therapeutic approaches to MS have been first validated in EAE. Nevertheless, EAE in all its modifications is not able to recapitulate the full range of clinical and histopathogenic aspects of MS. Furthermore, autoimmune reactions in EAE-prone rodent strains and MS patients may differ in terms of the relative involvement of various subsets of immune cells. However, the role of specific molecules that play a role in skewing the immune response towards pathogenic autoreactivity is very similar in mice and humans. Thus, in this chapter, we will focus on the identification of a novel subset of inflammatory T cells, called Th17 cells, in EAE and their interplay with other immune cells including protective regulatory T cells (T-regs). It is likely that the discovery of Th17 cells and their relationship with T-regs will change our understanding of organ-specific autoimmune diseases in the years to come.

Experimental autoimmune encephalomyelitis in the mouse

This unit details the materials and methods required for both active induction and adoptive transfer of experimental autoimmune encephalomyelitis (EAE) in the SJL mouse strain using intact proteins or peptides from the two major myelin proteins: proteolipid protein (PLP) and myelin basic protein (MBP). Detailed materials and methods required for the purification of both PLP and MBP are also described. Modifications of the specified protocols may be necessary for efficient induction of active or adoptive EAE in other mouse strains.

Prevention of Experimental Autoimmune Encephalomyelitis by Transfer of Embryonic Stem Cell-Derived Dendritic Cells Expressing Myelin Oligodendrocyte Glycoprotein Peptide along with TRAIL or Programmed Death-1 Ligand

Experimental autoimmune encephalomyelitis (EAE) is caused by activation of myelin Ag-reactive CD4+ T cells. In the current study, we tested a strategy to prevent EAE by pretreatment of mice with genetically modified dendritic cells (DC) presenting myelin oligodendrocyte glycoprotein (MOG) peptide in the context of MHC class II molecules and simultaneously expressing TRAIL or Programmed Death-1 ligand (PD-L1). For genetic modification of DC, we used a recently established method to generate DC from mouse embryonic stem cells (ES cells) in vitro (ES-DC). ES cells were sequentially transfected with an expression vector for TRAIL or PD-L1 and an MHC class II-associated invariant chain-based MOG epitope-presenting vector. Subsequently, double-transfectant ES cell clones were induced to differentiate to ES-DC, which expressed the products of introduced genes. Treatment of mice with either of the double-transfectant ES-DC significantly reduced T cell response to MOG, cell infiltration into spinal cord, and the severity of MOG peptide-induced EAE. In contrast, treatment with ES-DC expressing MOG alone, irrelevant Ag (OVA) plus TRAIL, or OVA plus PD-L1, or coinjection with ES-DC expressing MOG plus ES-DC-expressing TRAIL or PD-L1 had no effect in reducing the disease severity. In contrast, immune response to irrelevant exogenous Ag (keyhole limpet hemocyanin) was not impaired by treatment with any of the genetically modified ES-DC. The double-transfectant ES-DC presenting Ag and simultaneously expressing immune-suppressive molecules may well prove to be an effective therapy for autoimmune diseases without inhibition of the immune response to irrelevant Ag.

Expression of the tyrosine phosphatase SRC homology 2 domain-containing protein tyrosine phosphatase 1 determines T cell activation threshold and severity of experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is a CD4 Th1-mediated inflammatory demyelinating disorder of the CNS and a well-established animal model for multiple sclerosis. Src homology 2 domain-containing protein tyrosine phosphatase 1 (SHP-1) is a cytosolic tyrosine phosphatase that is involved in regulating the T cell activation cascade from signals initiated through the TCR. To study the role of SHP-1 in EAE pathogenesis, we immunized B10.PL mice heterozygous for deletion of the SHP-1 gene (me(v+/-)) and B10.PL wild-type mice with the immunodominant epitope of myelin basic protein (MBP Ac1-11). T cell proliferation and IFN-gamma production were significantly increased in me(v+/-) mice after immunization with MBP Ac1-11. The frequency of MBP Ac1-11-specific CD4 T cells, analyzed by staining with fluorescently labeled tetramers (MBP1-11[4Y]: I-A(u) complexes), was increased in the draining lymph node cells of me(v+/-) mice compared with wild-type mice. In addition, me(v+/-) mice developed a more severe course of EAE with epitope spreading to proteolipid protein peptide 43-64. Finally, expansion of MBP Ac1-11-specific T cells in response to Ag was enhanced in me(v+/-) T cells, particularly at lower Ag concentrations. These data demonstrate that the level of SHP-1 plays an important role in regulating the activation threshold of autoreactive T cells.

Diversity in MHC class II antigen presentation

Processing exogenous and endogenous proteins for presentation by major histocompatibility complex (MHC) molecules to T cells is the defining function of antigen-presenting cells (APC) as major regulatory cells in the acquired immune response. MHC class II-restricted antigen presentation to CD4 T cells is achieved by an essentially common pathway that is subject to variation with regard to the location and extent of degradation of protein antigens and the site of peptide binding to MHC class II molecules. These subtle variations reveal a surprising flexibility in the ways a diverse peptide repertoire is displayed on the APC surface. This diversity may have profound consequences for the induction of immunity to infection and tumours, as well as autoimmunity and tolerance.

Requirement for endocytic antigen processing and influence of invariant chain and H-2M deficiencies in CNS autoimmunity

The role of processing in antigen (Ag) presentation and T cell activation in experimental allergic encephalomyelitis (EAE) was evaluated in wild-type mice, mice that selectively express either Ii p31 or p41, and mice completely deficient in Ii or H-2M. We demonstrate that processing of myelin oligodendrocyte glycoprotein (MOG) is required for presentation of the dominant encephalitogenic MOG epitope, p35-55. Ii p31- and p41-expressing mice developed EAE with similar incidence to wild-type mice, although p41 mice had a more severe course. Ag-presenting cells (APCs) from Ii- or H-2M-deficient mice could present p35-55, but not MOG, demonstrating that these APCs could not process native MOG. Ii- and H-2M-deficient mice were not susceptible to EAE by immunization with p35-55 or MOG or by adoptive transfer of encephalitogenic T cells. However, CD4+ T cells from p35-55-immunized H-2M-deficient mice proliferated, secreted IFN-gamma, and transferred EAE to wild-type, but not H-2M-deficient, mice. Thus, EAE resistance in H-2M-deficient mice is not due to an inability of APCs to present p35-55, or an intrinsic defect in the encephalitogenic T cell repertoire, but reflects a defect in APC function. Our results indicate that processing is required for initial Ag presentation and CNS T cell activation and suggest that autopathogenic peptides of CNS autoantigen may not be readily available for presentation without processing.

Genetic background for immune-mediated diseases

Gene variants (alleles) involved in the immune response are most likely selected during evolution. The allelic polymorphisms that may be advantageous in fighting harmful agents may be susceptibility genes in immune-mediated diseases. Identification of susceptibility genes is important because these genes encode proteins, which are most probably involved in the disease process. Hence, the identification of susceptibility genes may lead to an improved understanding of the pathogenesis and may therefore help the development of preventive and therapeutic measures. Susceptibility genes may be identified by analyzing genes known to be involved in immune responses (candidate gene search) or by analyzing gene markers evenly distributed over the genome (genome-wide scan). However, since several genes jointly contribute to disease susceptibility, the frequencies of single susceptibility genes may be quite high in the normal population. Moreover, different set of genes may predispose to the same clinical disease. It may therefore be very difficult to identify susceptibility genes, apart from the major histocompatibility complex (MHC) genes, which have now been shown to predispose to several immune-mediated diseases.

Prevention of experimental autoimmune encephalomyelitis by encephalitogenic epitope sequence simplified derivatives

The encephalitogenic epitope P81-100 from mouse myelin basic protein was used to generate two simplified derivatives with glycine substitutions in alternating positions which were tested for their biological activity in a murine model of multiple sclerosis, experimental autoimmune encephalomyelitis. While both derivatives were unable to induce in mice the disease at the same parent peptide P81-100 dosage, T cell proliferation assays demonstrated their ability to compete with the parental peptide in a dose related manner. Experiments of cell surface binding and T cell tolerance revealed a different behavior of the two derivatives, suggesting different roles in the MHC blockade or T cell tolerance. On induction of encephalomyelitis in animals by P81-100 treatment, one variant proved in vivo to be very effective in protecting from the disease.

Pathogenesis, diagnosis, and treatment of acute disseminated encephalomyelitis

Acute disseminated encephalomyelitis is considered a monophasic, inflammatory demyelinating disorder of the central nervous system. A temporal relationship usually exists between the onset of neurologic symptoms and an infection or a vaccination. A viral exanthem facilitates the diagnosis. Some heterogeneity exists with regard to etiology and clinical course of this disease. Immunosuppression is considered the treatment of choice.

Tolerance and autoimmunity in TCR transgenic mice specific for myelin basic protein

T-cell receptor (TCR) transgenic mice provide the ability to follow the maturation and fate of T cells specific for self-antigens in vivo. This technology represents a major breakthrough in the study of autoimmune diseases in which specific antigens have been implicated. Proteins expressed within the central nervous system are believed to be important autoantigens in multiple sclerosis. TCR transgenic models specific for myelin basic protein (MBP) allowed us to assess the role of tolerance in providing protection from T cells with this specificity. Our studies demonstrate that T cells specific for the immunodominant epitope of MBP do not undergo tolerance in vivo and that TCR transgenic mice are susceptible to spontaneous autoimmune disease. The susceptibility to spontaneous disease is dependent on exposure to microbial antigens. MBP TCR transgenic models expressing TCRs specific for the same epitope of MBP but utilizing different V alpha genes exhibit differing susceptibilities to spontaneous disease. These data support the idea that genetic and environmental differences play a role in susceptibility to autoimmunity. MBP TCR transgenic models are playing an important role in defining mechanisms by which infectious agents trigger autoimmune disease as well as defining mechanisms by which tolerance is induced to distinct epitopes within self-antigens.

Microbial epitopes act as altered peptide ligands to prevent experimental autoimmune encephalomyelitis

Molecular mimicry refers to structural homologies between a self-protein and a microbial protein. A major epitope of myelin basic protein (MBP), p87-99 (VHFFKNIVTPRTP), induces experimental autoimmune encephalomyelitis (EAE). VHFFK contains the major residues for binding of this self-molecule to T cell receptor (TCR) and to the major histocompatibility complex. Peptides from papilloma virus strains containing the motif VHFFK induce EAE. A peptide from human papilloma virus type 40 (HPV 40) containing VHFFR, and one from HPV 32 containing VHFFH, prevented EAE. A sequence from Bacillus subtilis (RKVVTDFFKNIPQRI) also prevented EAE. T cell lines, producing IL-4 and specific for these microbial peptides, suppressed EAE. Thus, microbial peptides, differing from the core motif of the self-antigen, MBPp87-99, function as altered peptide ligands, and behave as TCR antagonists, in the modulation of autoimmune disease.

Acquired thymic tolerance and experimental allergic encephalomyelitis in the rat. I. Parameters and analysis of possible mechanisms

Intrathymic injection of guinea pig myelin basic protein (MBP) or the immunodominant, encephalitogenic fragment of MPB, 68-86, without otherwise compromising the peripheral lymphocyte pool in adult LEW rats, dramatically inhibits onset of experimental allergic encephalomyelitis (EAE) caused by the usual peripheral inoculation with MBP in complete Freund's adjuvant. This surprising finding demonstrates that interaction of antigen and one or more components of an intact thymus can down-regulate systemic responses by mature T cells already existing in the peripheral lymphocyte pool. How this happens is not known. In studies designed to explore possible mechanisms: (a) adult thymectomized animals remain susceptible to active EAE, thus EAE cannot be attributed solely to recent thymic emigrants that might be inactivated by antigen deposited in the thymus; (b) heterotopic isografts of injected thymic lobes transfer thymic tolerance to secondary recipients, thus the tolerance effect is dominant over an intact, non-treated thymus; (c) T cells from made thymic tolerant but not immunized donors are less effective in causing EAE following adoptive transfer into, and active immunization of, secondary, irradiated recipients; and (d) animals resistant to active EAE as a consequence of thymic tolerance are fully vulnerable to adoptive EAE caused by already activated MBP-specific T cell subpopulations. These results rule out a possible mechanism previously proposed for acquired thymic tolerance, i. e., that potentially pathogenic T cells traffic to the antigen-injected thymus where they are inactivated or eliminated.

Differential tolerance is induced in T cells recognizing distinct epitopes of myelin basic protein

Experimental allergic encephalomyelitis (EAE) is induced by T cell-mediated immunity to central nervous system antigens. In H-2u mice, EAE is mediated primarily by T cells specific for residues 1-11 of myelin basic protein (MBP). We demonstrate that differential tolerance to MBP1-11 versus epitopes in MBP121-150 is induced by expression of endogenous MBP, reflecting extreme differences in stability of peptide/MHC complexes. The diverse MBP121-150-specific TCR repertoire can be divided into three fine specificity groups. Two groups were identified in wild-type mice despite extensive tolerance, but the third group was not detected. Activated MBP121-150-specific T cells induce EAE in wild-type mice. Thus, encephalitogenic T cells that escape tolerance either recognize short-lived peptide/MHC complexes or express TCRs with unique specificities for stable complexes.

Analysis of TCR beta chains in Lewis rats with experimental allergic encephalomyelitis. II. Vbeta8.2+ T cells with limited CDR3 N region additions derive from the adult thymus

Immunization of Lewis (LEW) rats with guinea pig myelin basic protein (MBP) induces a population of encephalitogenic CD4 T cells having specificity for the dominant immunogenic peptide of MBP, 68-86. The TCR beta chains of these disease-causing T cells show three distinct features: they are almost exclusively Vbeta8.2, they use AspSer as the first two amino acid residues of the third complementarity-determining region (CDR3) and these junctional region sequences show few if any non-germline N-region nucleotide additions. This last feature raises the possibility that these autoimmune T cell precursors derive from TCR gene rearrangements occurring during early, perinatal ontogeny, a period when the enzyme terminal deoxynucleotidyl transferase (TdT), responsible for N region additions, is not expressed. An alternative possibility is that these features of the TCR of MBP 68-86-reactive T cells are dictated by considerations of antigen selection throughout ontogeny both in the thymus and in the periphery--ie., that such beta chains are conformationally the most appropriate for triggering by an epitope of 68-86 complexed to class II RT1.BI MHC molecules. We show here that active experimental allergic encephalomyelitis, while delayed in onset, occurs in heavily irradiated animals, but not in the absence of a thymus, a finding indicating that this autoimmune disease is caused by a T cell subpopulation derived from the post-irradiation adult thymus. These disease-causing T cells are heavily Vbeta8.2+, CDR3 AspSer+ and use few N region additions. We conclude that T cells with these TCR beta chain features can be generated in the adult thymus and most likely reflect requirements imposed by antigen selection.

Suppressive vaccination with DNA encoding a variable region gene of the T-cell receptor prevents autoimmune encephalomyelitis and activates Th2 immunity

A variable region gene of the T-cell receptor, V beta 8.2, is rearranged, and its product is expressed on pathogenic T cells that induce experimental autoimmune encephalomyelitis (EAE) in H-2u mice after immunization with myelin basic protein (MBP). Vaccination of these mice with naked DNA encoding V beta 8.2 protected mice from EAE. Analysis of T cells reacting to the pathogenic portion of the MBP molecule indicated that in the vaccinated mice there was a reduction in the Th1 cytokines interleukin-2 (IL-2) and interferon-gama. In parallel, there was an elevation in the production of IL-4, a Th2 cytokine associated with suppression of disease. A novel feature of DNA immunization for autoimmune disease, reversal of the autoimmune response from Th1 to Th2, may make this approach attractive for treatment of Th1-mediated diseases like multiple sclerosis, juvenile diabetes and rheumatoid arthritis.

Exacerbated autoimmunity associated with a T helper-1 cytokine profile shift in H-2E-transgenic mice

Major histocompatibility complex (MHC) class II genes are the strongest susceptibility markers for many human autoimmune diseases. A perplexing aspect of this is that HLA alleles can confer either susceptibility or dominant protection. In nonobese diabetic (NOD) mice, the strongest known diabetes susceptibility locus is within the MHC and is presumed to be the H-2Ag7 product. When NOD mice carry a transgenic E alpha d molecule allowing expression of an H-2E heterodimer, diabetes is prevented. We investigated whether, as in human autoimmunity, a single class II heterodimer might protect from some autoimmune diseases while predisposing to others. NOD mice are susceptible to experimental autoimmune encephalomyelitis (EAE) induced by the proteolipoprotein (PLP) epitope 56-70. Susceptibility to EAE was analyzed in NOD mice which either have or lack transgenic H-2E expression. We found that H-2E expression in NOD mice has converse effects on diabetes and EAE: while diabetes is prevented, EAE is greatly exacerbated and leads to demyelination. Although PLP 56-70 could be presented both in the context of H-2A and H-2E, increased disease severity in H-2E transgenic mice could not be attributed either to an enhanced T cell proliferative response to PLP or to differences in determinant spread. However, cytokine analysis of the response revealed important differences between NOD mice and their H-2E transgenic counterparts: H-2E expression was associated with reduced interleukin-4 secretion and enhanced interferon-gamma (IFN-gamma) secretion by lymph node cells, while the response of central nervous system infiltrating T cells displayed a markedly enhanced IFN-gamma response. Thus, whether a particular class II molecule confers resistance or susceptibility to an autoimmune disease may depend on differential cytokine profiles elicited by particular class II/autoantigen complexes.

Studies on T-cell receptors involved in experimental autoimmune encephalomyelitis using the complementary peptide recognition approach

Based upon Blalock's complementary recognition approach, a complementary or antisense peptide (CP) was designed to the experimental autoimmune encephalomyelitis (EAE) epitope peptide, rat myelin basic protein (MBP) peptide 72-82. This peptide (EAE CP) was shown to have some sequence similarities to T-cell receptors (TCR) and MHC II molecules in a sequence homology search. Solid-phase binding assays demonstrated specific and high affinity binding (3 and 4 microM) between the EAE CP and the rat and guinea pig EAE epitope peptides (Rt72-82 and Gp69-82), respectively. This EAE CP was also found to be immunogenic in rats in an ear swelling test for delayed type hypersensitivity (DTH) reactions and an ELISA for antibody responses. However, a rabbit antibody generated to EAE CP was shown to be unable to stain the V beta 8+ EAE susceptible T-cells in immunofluorescence analyses. This EAE CP was also used in attempts to down-regulate EAE and the results showed that prior immunization with EAE CP in complete Freund's adjuvant could not prevent the Lewis rats from developing EAE. Although the data on sense-antisense peptide interaction were positive and the EAE CP was immunogenic, the inability of EAE CP to regulate EAE indicates that the CP approach may not be generally applicable.

Mechanisms of acquired thymic tolerance in experimental autoimmune encephalomyelitis: thymic dendritic-enriched cells induce specific peripheral T cell unresponsiveness in vivo

Experimental autoimmune encephalomyelitis (EAE), an experimental model for the study of multiple sclerosis, is an autoimmune disease of the central nervous system that can be induced in a number of species by immunization with myelin basic protein (MBP). MBP-reactive CD4+ T cells, predominantly expressing the V beta 8.2 T cell receptor (TCR), migrate from the peripheral lymphoid organs and initiate the inflammatory response in the brain. We have previously shown that a single intrathymic injection of MBP or its major encephalitogenic peptide (p71-90), but not a nonencephalitogenic peptide (p21-40), induces antigen-specific systemic tolerance and inhibits the induction of EAE in Lewis rats. In this study, we investigated the mechanisms of induction and maintenance of acquired thymic tolerance in this model. First, we investigated which thymic cell is responsible for "induction" of systemic tolerance. Thymic dendritic-enriched cells, isolated by plastic adherence, when incubated in vitro with p71-90 and injected intravenously into Lewis rats, were capable of preventing the development of EAE, but his protection was lost in thymectomized recipients. In addition, intravenous injection of thymic dendritic cells isolated from animals that had been previously injected intrathymically with p71-90 but not p21-40 also prevented the development of EAE. Second, to determine the "effector" mechanisms involved in acquired thymic tolerance, we compared TCR expression in the brains of animals with actively induced EAE with TCR expression in animals that received intrathymic injection of p71-90 or p21-40. Using a semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) technique, we found increased expression of CD4 and V beta 8.2 message in brains of immunized animals compared with those of naive animals. In animals intrathymically injected with p71-90 but not p21-40, CD4 and V beta 8.2 transcript levels were significantly reduced compared with immunized controls. Immunohistologic studies of brain tissue and spleens with specific V beta 8.2 and control V beta 10 monoclonal antibodies confirmed these observations in vivo. These findings, taken together with recent data demonstrating that activated T cells circulate through the thymus, suggest that interaction of thymic dendritic cells with specific TCR of activated peripheral T cells can lead to inactivation of these antigen-specific cells and confirm the role of V beta 8.2-expressing T cells in EAE.

Functional evidence for epitope spreading in the relapsing pathology of experimental autoimmune encephalomyelitis

The role of epitope spreading in the pathology of relapsing-remitting experimental autoimmune encephalomyelitis (R-EAE) was examined. Using peripherally induced immunologic tolerance as a probe to analyze the neuropathologic T cell repertoire, we show that the majority of the immunopathologic reactivity during the acute phase of R-EAE in SJL/J mice induced by active immunization with the intact proteolipid (PLP) molecule is directed at the PLP139-151 epitope and that responses to secondary encephalitogenic PLP epitopes may contribute to the later relapsing phases of disease. Intermolecular epitope spreading was demonstrated by showing the development of T cell responses to PLP139-151 after acute disease in mice in which R-EAE was initiated by the transfer of T cells specific for the non-cross-reactive MBP84-104 determinant. Intramolecular epitope spreading was demonstrated by showing that endogenous host T cells specific for a secondary encephalitogenic PLP epitope (PLP178-191) are demonstrable by both splenic T cell proliferative and in vivo delayed-type hypersensitivity responses in mice in which acute central nervous system damage was initiated by T cells reactive with the immunodominant, non-cross-reactive PLP139-151 sequence. The PLP178-191-specific responses are activated as a result of and correlate with the degree of acute tissue damage, since they do not develop in mice tolerized to the initiating epitope before expression of acute disease. Most importantly, we show that the PLP178-191-specific responses are capable of mediating R-EAE upon adoptive secondary transfer to naive recipient mice. Furthermore, induction of tolerance to intact PLP (which inhibits responses to both the initiating PLP139-151 epitope and to the PLP178-191 epitope) after the acute disease episode is sufficient to prevent relapsing disease. These results strongly support a contributory role of T cell responses to epitopes released as a result of acute tissue damage to the immunopathogenesis of relapsing clinical episodes and have important implications for the design of antigen-specific immunotherapies for the treatment of chronic autoimmune disorders in humans.

Self and non-self peptides treat autoimmune encephalomyelitis: T cell anergy or competition for major histocompatibility complex class II binding?

In susceptible strains of mice, myelin basic protein (MBP) peptide Acl-ll induces experimental autoimmune encephalomyelitis (EAE) providing a useful model for human multiple sclerosis. Acl-11 binds major histocompatibility complex (MHC) class II molecules A alpha upsilon A beta upsilon. Here, we show that the Acl-11 peptide, when administered intraperitoneally in incomplete Freund's adjuvant (IFA) emulsion, can effectively treat Acl-11-induced EAE in mice. Treatment with Acl-11/IFA 9 days after initial immunization with Acl-11 in complete Freund's adjuvant (CFA) results in a loss of T cell proliferation to MBP Acl-11. This lack of T cell proliferation is not due to T cell anergy and is not specific. A similar lack of T cell proliferation and inhibition of EAE is observed when an ovalbumin peptide OVA323-339 or a sperm whale myoglobin peptide SWM110-121 are used to treat mice immunized with Acl-11. Interestingly, we show that previously unresponsive lymph node cells from treated mice respond normally if Acl-11 is presented by fresh antigen-presenting cells taken from normal mice. These results argue that the lack of T cell proliferation and inhibition of EAE is not due to specific T cell anergy as suggested by others. Instead this appears to be due to blocking of MHC class II molecules A alpha upsilon A beta upsilon by the treating peptides.

Evolution of the T-cell repertoire during the course of experimental immune-mediated demyelinating diseases

Fig. 6 depicts a model for epitope spreading in T cell-mediated demyelination. The acute phase of disease is due to T cells specific for the initiating epitope, which can be either a determinant on the CNS target organ of the autoimmune response or a determinant on a persisting, CNS-tropic virus. The primary T cell response is responsible for the initial tissue damage by the production of proinflammatory Th1 cytokines which can affect myelination directly (Selmaj et al. 1991) and indirectly by their ability to recruit and activate macrophages to phagocytize myelin (Cammer et al. 1978). As a result of myelin damage and opening of the blood-brain-barrier during acute disease, T cells specific for endogenous epitopes on the same and/or different myelin proteins are primed and expand either in the periphery or locally in the CNS. These secondary T cells initiate an additional round of myelin destruction, leading to a clinical relapse by production of additional pro-inflammatory cytokines, similar to the bystander demyelination operative during acute disease. It will be of great interest to determine the relative contributions of local and systemic immune responses to these endogenous neuroepitopes. It is possible that local CNS presentation of endogenous neuroepitopes following acute CNS damage could be mediated by infiltrating inflammatory macrophages, activated microglial cells, endothelial cells and/or astrocytes. These tissue resident antigen presenting cells have been shown to upregulate expression of MHC class II (Sakai et al. 1986, Traugott & Lebon 1988), certain adhesion molecules (Cannella et al. 1990), and B7 costimulatory molecules (K. M. Nikcevich, J. A. Bluestone, and S. D. Miller, in preparation) in response to pro-inflammatory cytokines. The data on epitope spreading provided by the murine demyelinating disease models clearly illustrate the dynamic nature of the T cell repertoire during chronic inflammation in a specific target organ. The contribution of epitope spreading to chronic CNS demyelination could be considered to be a special case since tolerance to myelin epitopes would be expected to be inefficient due to their sequestration behind the blood-brain-barrier. However, the recent description of epitope spreading in response to pancreatic antigens in spontaneous diabetes in the NOD mouse may indicate that this phenomenon is operative in a variety of organ-specific experimental and spontaneous autoimmune diseases.(ABSTRACT TRUNCATED AT 400 WORDS)

Experimental allergic encephalomyelitis (EAE) in mice lacking CD4+ T cells

Like most experimental autoimmune disease experimental allergic encephalomyelitis (EAE) has been shown to be mediated by CD4+ helper T cells. In vivo antibody blocking studies with anti-CD4 and adoptive transfer of activated CD4+ T cells indicate the importance of CD4+ cells in disease induction. Fourth backcross generation mutant CD4-/-PL/J mice were immunized with myelin basic protein. Despite the lack CD4+ T cells some of these mice developed EAE, albeit, at a considerably reduced frequency and with variable severity. Furthermore, antigen-specific T cell proliferation can be demonstrated, indicating some residual helper activity that is major histocompatibility complex class II restricted. This demonstrated that, although the CD4+ T cell is the prime effector cell in EAE, in mice developmentally lacking in CD4, the expanded double-negative T cells may subserve helper and effector functions.

Holes in the T cell repertoire to myelin basic protein owing to the absence of the D beta 2-J beta 2 gene cluster: implications for T cell receptor recognition and autoimmunity

Models of T cell recognition suggest that amino acid residues in the CDR3 region of the T cell receptor (TCR) alpha or beta chain directly contact the major histocompatibility complex-bound peptide, and thus are crucial for providing peptide specificity. T cells derived from B10.PL or PL/J mice of H-2u haplotype, use only D beta 2 and J beta 2 gene segments in the recognition of the dominant determinant, Ac1-9/Au, of myelin basic protein (MBP). New Zealand White (NZW) mice, with identical class II H-2u genes (I-A and I-E), carry an 8.8-kb deletion in their TCR beta chain locus encompassing D beta 2 and J beta 2 gene segments. How does this deletion of the crucial D beta 2-J beta 2 region in NZW mice influence specific responses to Ac1-9/Au as well as to other known Au or Eu determinants of MBP? We found that these mice respond very poorly to the dominant Ac1-9/Au and to the subdominant 31-50/Eu determinant in in vitro proliferation assays as well as in their in vivo capacity to induce experimental autoimmune encephalomyelitis. This loss of response is apparently owing to the absence of high avidity TCRs with essential CDR3 residues contributed by D beta 2 or J beta 2 gene segments. These data reveal constraints in the recognition of certain antigenic structures, and further support a TCR-recognition model in which CDR3 residues of the TCR alpha and beta chains constitute the antigenic peptide-binding sites on the TCR molecule. Implications for autoimmune manifestations contributed by NZW genes in (NZB x NZW)F1 disease are also discussed.

Acquired tolerance to experimental autoimmune encephalomyelitis by intrathymic injection of myelin basic protein or its major encephalitogenic peptide

Experimental autoimmune encephalomyelitis (EAE) is an inflammatory disease of the central nervous system that can be induced in a number of species by immunization with myelin basic protein (MBP) in adjuvant, and serves as an experimental model for the study of multiple sclerosis. The role of the thymus in acquired tolerance in autoimmune models has not been thoroughly investigated. In this study, we examined the effects of intrathymic injection of MBP or its major encephalitogenic peptide on the course of EAE in Lewis rats. A single intrathymic injection of MBP 48 h pre- but not postimmunization protects animals from actively induced EAE. An intact MBP-primed thymus was required up to 10 d postimmunization, as thymectomy on days 1, 2, and 7 postimmunization abrogated the protective effect, whereas thymectomy on day 10 did not. The proliferative response of primed lymphocytes was significantly reduced in animals that were intrathymically injected with MBP. Protection against clinical EAE was induced by thymic injection of the major encephalitogenic region (residues 71-90) but not a nonencephalitogenic (21-40) MBP epitope. Immunohistologic examination of the brain from rats intrathymically injected with encephalitogenic peptide showed markedly reduced cellular infiltrate and virtual absence of activation and inflammatory cytokines as compared with rats intrathymically injected with the nonencephalitogenic peptide. These results indicate that the thymus may play an active role in acquired systemic immunologic tolerance in T cell-mediated experimental autoimmune diseases. This effect may be mediated by a process of clonal inactivation of autoreactive T cell clones circulating through the thymus.

Prevention of experimental autoimmune arthritis with a peptide fragment of type II collagen

Collagen arthritis is induced in inbred rats with the injection of native type II collagen. The pathogenesis of this experimental autoimmune disease is T cell dependent. This study demonstrates that collagen-specific T cells, derived from pathogenic and nonpathogenic rat T cell lines, both recognize the same peptide epitope. The epitope, consisting of amino acids 58-73 of cyanogen bromide fragment 11 of type II collagen, was as effective as whole collagen in stimulating a panel of collagen-specific rat/mouse T cell hybridomas. This peptide may, therefore, constitute a dominant epitope for CD4+ rat T cells in their response to type II collagen. Administration of the peptide to either neonatal or adult rats prevented the subsequent induction of experimental arthritis with whole collagen, demonstrating that the in vivo response to this dominant epitope is, therefore, relevant in the pathogenesis of arthritis. Despite its ability to prevent collagen-induced arthritis, administration of this peptide in incomplete Freund's adjuvant intradermally did not induce disease.

Epitope specificity and TCR V beta gene utilization in the encephalitogenic response of B10.RIII(71NS)/SnJ mice

A high proportion of peptide 1-11 specific T cells from H-2u (V beta 8+, H-2u) mice express the V beta 8 TCR chain. Peptide 89-101 is immunodominant for B10.RIII (V beta 8+, H-2r) mice; thus, it was of interest to determine whether V beta 8 TCR would be over-represented in a population of peptide 89-101-specific T cells of this strain. Second, it was asked whether MBP peptides other than 89-101 would induce EAE in these mice. Of 70 B10.RIII(71NS)/SnJ mice immunized with mouse myelin basic protein (MBP), 32 of 41 males (78%) and 11 of 29 females (38%) showed clinical signs of experimental allergic encephalomyelitis (EAE). All mice immunized with peptide 89-101 showed clinical signs. One of six mice immunized with peptide 91-103 showed clinical signs, and 9 of 16 mice, all males, responded with EAE when immunized with peptide 38-88. No clinical EAE was observed in mice immunized with peptide 43-67, 68-88, 55-74, 1-37 or 1-20. A peptide 89-101-specific T cell line was established. At the initial stimulation the line was 29% V beta 8+ versus 21% in normal controls, and the line did not transfer EAE adoptively. After five in vitro stimulations, the percentage of V beta 8+ T cells had increased to 54%, and the line was encephalitogenic. Encephalitogenicity was partially blocked by anti-V beta 8 monoclonal antibody. Thus, over-representation of V beta 8+ TCR by encephalitogenic peptide-specific T cells is not limited to peptide 1-11-specific T cells from H-2u mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Amelioration of autoimmune encephalomyelitis by myelin basic protein synthetic peptide-induced anergy

Experimental autoimmune encephalomyelitis (EAE), a demyelinating disease of the central nervous system that can be induced in susceptible strains of mice by immunization with myelin basic protein (MBP) or its immunodominant T cell determinants, serves as a model of human multiple sclerosis. Tolerance to MBP in adult mice was induced by intraperitoneal injection of synthetic peptides of immunodominant determinants of MBP and prevented MBP-induced EAE. Furthermore, tolerance-inducing regimens of peptides administered to mice after the disease had begun (10 days after induction with MBP) blocked the progression and decreased the severity of EAE. Peptide-induced tolerance resulted from the induction of anergy in proliferative, antigen-specific T cells.

Experimental allergic encephalomyelitis in susceptible and resistant strains of mice after adoptive transfer of T cells activated by antibodies to the T cell receptor complex

Lymphoid cells from normal and myelin basic protein (MBP)-immune PL/J, SJL/J and (SJL x PL)F1 hybrid mice were activated by in vitro culture with monoclonal antibodies specific for CD3 or specific T cell receptor (TCR) V beta chains. Lymphoid cells activated in this manner from MBP-immune animals did not readily transfer experimental acute encephalomyelitis (EAE) to naive syngeneic recipients in contrast to lymphoid cells from the same source cultured with concanavalin A (ConA) or myelin basic protein (MBP). However, recipients of anti-TCR antibody-activated MBP-specific blasts showed accelerated onset and increased severity of EAE following immunization with MBP as compared to unmanipulated control animals. Anti-TCR activated cells incorporated [3H]-thymidine at a level comparable to ConA or antigen-stimulated cells and secreted interleukin (IL)-2 at comparable levels Anti-TCR activated blasts were greater than 90% positive for CD3 and alpha/beta TCR, 60% CD4+ and 30% CD8+. PL/J or (SJL x PL)F1 recipients of anti-TCR-activated spleen cells from syngeneic normal mice also had more severe EAE than control mice following immunization with MBP. Non-responder C57BL/10SnJ mice could be converted to responders by infusion of anti-CD3 or anti-V beta 8 monoclonal antibody-treated syngeneic spleen cells taken from normal syngeneic unimmunized mice.

Subjugation of dominant immunogenic determinants within a chimeric peptide

The mechanism of immunodominance was investigated using chimeric peptides from mouse myelin basic protein consisting of the immunodominant I-Au-restricted Ac1-11, attached by a peptide bond to I-Eu-restricted 35-47. Our results indicate that this chimeric peptide and certain of its derivatives were excellent immunogens both in vitro and in vivo. Notably, on immunization with Ac1-11:35-47 or Ac1-11 (Ala4):35-47, the proliferative T cell responses to each of its component peptides were almost completely "subjugated" in favor of neo-determinants that are I-Eu restricted. Furthermore, each of 11 hybridomas derived after immunization with Ac1-11:35-47 had specificity for junctional neo-determinants and none could be stimulated to produce interleukin-2 from Ac1-11 or 35-47. Subjugation of the immunogenicity of the original determinants occurred regardless of their dominance when separate. It did not appear to result from non-availability of the original determinants because the chimeric peptide was able to induce neonatal tolerance to each of its constituents. These results indicate that in an overlapping multideterminant array, the dominant determinant is unpredictable from historical data about any of the components. Determinant choice, at any stage of processing, may be governed by competitive aspects of determinant capture in an environment where all components--antigen, major histocompatibility complex and T cell receptor--are available.

Spreading of T-cell autoimmunity to cryptic determinants of an autoantigen

Immunization with myelin basic protein (MBP) induces experimental allergic encephalomyelitis (EAE), a prototype of CD4+ T-cell mediated autoimmune disease. In rodents, MBP-reactive T-cell clones are specific for a single, dominant determinant on MBP and use a highly restricted number of T-cell receptor genes. Accordingly, EAE has been prevented by various receptor-specific treatments, suggesting similar strategies may be useful for therapy of human autoimmune disease. Here we report that in (SJL x B10.PL)F1 mice, immune dominance of a single determinant, MBP:Ac1-11, is confined to the inductive phase of EAE. In mice with chronic EAE, several additional determinants of MBP in peptides 35-47, 81-100 and 121-140 recall proliferative responses. Most importantly, reactivity to the latter determinants was also detected after induction of EAE with MBP peptide Ac1-11 alone; this demonstrates priming by endogenous MBP determinants. Thus, determinants of MBP that are cryptic after primary immunization can become immunogenic in the course of EAE. Diversification of the autoreactive T-cell repertoire due to 'determinant spreading' has major implications for the pathogenesis of, and the therapeutic approach to, T-cell driven autoimmune disease.

Myelin proteolipid protein: minimum sequence requirements for active induction of autoimmune encephalomyelitis in SWR/J and SJL/J mice

Proteolipid protein (PLP) is the major protein constituent of mammalian central nervous system myelin. We have previously identified two different PLP encephalitogenic T cell epitopes in two mouse strains. Murine PLP peptides 103-116 YKTTICGKGLSATV and 139-151 HCLGKWLGHPDKF are encephalitogenic determinants in SWR/J (H-2q) and SJL/J (H-2s) mice, respectively. The purpose of the present study was to determine the minimum sequence requirements for each of these PLP encephalitogens. In SWR/J mice, at least two distinct overlapping peptides can induce experimental autoimmune encephalomyelitis (EAE). The eleven residue sequences PLP 105-115 TTICGKGLSAT and PLP 106-116 TICGKGLSATV are encephalitogenic in SWR/J mice, but PLP 106-115 TICGKGLSAT, the decapeptide indigenous to both sequences, is non-encephalitogenic. In contrast, the shortest PLP sequence capable of inducing EAE in SJL/J mice is the nonapeptide 141-149 LGKWLGHPD. These data indicate that encephalitogenic determinants of PLP are short contiguous peptide sequences similar in length and diversity to those of MBP.

Copolymer-1-induced inhibition of antigen-specific T cell activation: interference with antigen presentation

Copolymer-1 (Cop-1) has been shown to inhibit in vivo development of experimental allergic encephalomyelitis (EAE) in animals and has been reported to have some therapeutic benefit in relapsing/remitting multiple sclerosis (MS). The mechanism by which Cop-1 acts in vivo is not known. The present study demonstrates that Cop-1 inhibits the in vitro response of several antigen-specific murine T cell hybridomas restricted to I-A, and to a lesser extent, I-E. The ability of human myelin basic protein (MBP)-specific T cell lines (TCL) to lyse targets in the context of three HLA-DR types associated with MS was also impaired by Cop-1. The results suggest that the observed inhibition was due to competition between Cop-1 and nominal antigen for the class II major histocompatibility complex (MHC) peptide binding site.

An immunochemical comparison of human myelin basic protein and its modified, citrullinated form, C8

An immunochemical analysis was conducted to compare the C1 isomer of human myelin basic protein (MBP) with the newly described and less cationic, citrullinated isomer of MBP referred to as C8. Ten polyclonal antisera directed at multiple epitopes or restricted regions of MBP were used in radioimmunoassays to examine MBP-C1 and MBP-C8. Antisera reactive with MBP peptide 1-14 clearly distinguished MBP-C1 from MBP-C8. Antisera to human MBP peptides 10-19 and 90-170, but not to MBP peptide 69-89, showed modest differences between MBP-C1 and MBP-C8. The MBP-C8s from multiple sclerosis (MS) and non-MS brain reacted essentially the same. With murine monoclonal antibodies and enzyme-linked immunosorbent assay (ELISA), differences between MBP-C8 and other isomers were shown for anti-MBP 10-19 but not for anti-MBP 1-9 or anti-MBP 80-89. These findings imply differences in sequence or conformation in the structure of MBP-C7 compared to MBP-C1, most notably near the amino terminus.

EAE: a model for immune intervention with synthetic peptides

The cellular and molecular requirements for the autoimmune disease EAE are being defined in increasing detail through intense scrutiny of critical autoantigenic peptides, class II MHC molecules, and alpha beta TCRs involved in the disease process. This study has led to novel immunotherapeutic approaches, many of which are based on the administration of synthetic peptides. Since short peptides are understood to be the minimal antigenic units bound by MHC molecules for recognition by T cells, they are attractive experimental tools for finely modulating specific immune responses. It is clear that a large number of defined peptides can dramatically influence the course of EAE. Table IV lists a number of potential mechanisms which may mediate disease prevention. Increasing evidence supports the idea that prevention of autoimmune disease can result from MHC-blockade by peptides which competitively bind to class II molecules. However, for some peptides such as the perplexing partial agonist Ac1-11[4A], the mechanism by which these precisely defined units act is not yet fully understood. Numerous hurdles hinder immediate clinical application of peptide-based immunotherapy. Nevertheless, the knowledge gained by probing experimental autoimmunity with defined peptides promises to inspire original and practical approaches to treating human autoimmune disease.

A single amino acid change in a myelin basic protein peptide confers the capacity to prevent rather than induce experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is an experimental demyelinating disease of rodents. In (PL/J x SJL) F1 mice, it is induced by immunization with the myelin basic protein peptide Ac1-11. Ac1-11 [4A], a myelin basic protein peptide analog with a single amino acid substitution, (i) binds to class II major histocompatibility complex molecules and stimulates encephalitogenic T cells in vitro better than Ac1-11, (ii) is nonimmunogenic and nonencephalitogenic in vivo in (PL/J x SJL)F1 mice, (iii) prevents EAE when administered before or at the time of immunization with Ac1-11, and (iv) prevents EAE when administered later, near the time of disease onset. Initial studies suggest that Ac1-11 [4A] does not prevent EAE by competitive inhibition or by activation of regulatory cells. Thus, substitution of a single amino acid in a myelin basic protein peptide confers the capacity to prevent rather than induce EAE, even after peptide-specific encephalitogenic T cells have been activated.

Clonal diversity of basic protein specific T cells in Lewis rats recovered from experimental autoimmune encephalomyelitis

T cell lines selected from Lewis rats recovered from experimental autoimmune encephalomyelitis (EAE) respond not only to the immunodominant 72-89 epitope of basic protein (BP), but also to secondary epitopes including the I-A restricted 43-67 region of guinea pig (Gp) BP and the I-E restricted 87-99 sequence of rat (Rt) BP. The current study demonstrates at the clonal level the diversity of T cell responses to Gp- and Rt-BP in EAE-recovered rats. As predicted from the response pattern of BP-selected T cell lines, T cell clones from the lines responded to both the dominant and secondary epitopes of BP. In addition, a new majority clonal type was identified that responded to whole BP but not to epitopes represented on enzymatic cleavage fragments or synthetic peptides spanning the BP molecule. Clones representative of each of the three types of Gp-BP responses were characterized for phenotype, major histocompatibility complex restriction, and biologic activity in vivo. All of the clones were strongly CD4+ and co-expressed CD8 at modest levels as measured by both immunofluorescence and Northern blots. All three T cell specificities were I-A restricted. However, only the 72-89 responsive clone could transfer clinical EAE, due most likely to its unique ability to respond to Rt-BP. In contrast, the Gp-BP 43-67 reactive T cell clone transferred protection against EAE, whereas the whole Gp-BP reactive clone transferred delayed-type hypersensitivity response but was neither encephalitogenic nor protective. Thus, the recovery process from EAE is distinguished by an increased diversity of protective clones as well as innocuous clones that may be spawned as encephalitogenic T cells are regulated.