Pathways to cures for multiple sclerosis: A research roadmap

Background:

Multiple Sclerosis (MS) is a growing global health challenge affecting nearly 3 million people. Progress has been made in the understanding and treatment of MS over the last several decades, but cures remain elusive. The National MS Society is focused on achieving cures for MS.

Objectives:

Cures for MS will be hastened by having a roadmap that describes knowledge gaps, milestones, and research priorities. In this report, we share the Pathways to Cures Research Roadmap and recommendations for strategies to accelerate the development of MS cures.

Methods:

The Roadmap was developed through engagement of scientific thought leaders and people affected by MS from North America and the United Kingdom. It also included the perspectives of over 300 people living with MS and was endorsed by many leading MS organizations.

Results:

The Roadmap consist of three distinct but overlapping cure pathways: (1) stopping the MS disease process, (2) restoring lost function by reversing damage and symptoms, and (3) ending MS through prevention. Better alignment and focus of global resources on high priority research questions are also recommended.

Conclusions:

We hope the Roadmap will inspire greater collaboration and alignment of global resources that accelerate scientific breakthroughs leading to cures for MS.

Serum exosomes in pregnancy-associated immune modulation and neuroprotection during CNS autoimmunity

In multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE), relapses are markedly reduced during pregnancy. Exosomes are lipid-bound vesicles and are more abundant in the serum during pregnancy. Using murine EAE, we demonstrate that serum exosomes suppress T cell activation, promote the maturation of oligodendrocyte precursor cells (OPC), and pregnancy exosomes facilitate OPC migration into active CNS lesions. However, exosomes derived from both pregnant and non-pregnant mice reduced the severity of established EAE. Thus, during pregnancy, serum exosomes modulate the immune and central nervous systems and contribute to pregnancy-associated suppression of EAE.

Distinct populations of innate CD8+ T cells revealed in a CXCR3 reporter mouse

CXCR3, expressed mainly on activated T and NK cells, is implicated in a host of immunological conditions and can contribute either to disease resolution or pathology. We report the generation and characterization of a novel CXCR3 internal ribosome entry site bicistronic enhanced GFP reporter (CIBER) mouse in which enhanced GFP expression correlates with surface levels of CXCR3. Using CIBER mice, we identified two distinct populations of innate CD8(+) T cells based on constitutive expression of CXCR3. We demonstrate that CXCR3(+) innate CD8(+) T cells preferentially express higher levels of Ly6C and CD122, but lower levels of CCR9 compared with CXCR3(-) innate CD8(+) T cells. Furthermore, we show that CXCR3(+) innate CD8(+) T cells express higher transcript levels of antiapoptotic but lower levels of proapoptotic factors, respond more robustly to IL-2 and IL-15, and produce significantly more IFN-γ and granzyme B. Interestingly, CXCR3(+) innate CD8(+) T cells do not respond to IL-12 or IL-18 alone, but produce significant amounts of IFN-γ on stimulation with a combination of these cytokines. Taken together, these findings demonstrate that CXCR3(+) and CXCR3(-) innate CD8(+) T cells are phenotypically and functionally distinct. These newly generated CIBER mice provide a novel tool for studying the role of CXCR3 and CXCR3-expressing cells in vivo.

miR-29ab1 deficiency identifies a negative feedback loop controlling Th1 bias that is dysregulated in multiple sclerosis

Th cell programming and function is tightly regulated by complex biological networks to prevent excessive inflammatory responses and autoimmune disease. The importance of microRNAs (miRNAs) in this process is highlighted by the preferential Th1 polarization of Dicer-deficient T cells that lack miRNAs. Using genetic knockouts, we demonstrate that loss of endogenous miR-29, derived from the miR-29ab1 genomic cluster, results in unrestrained T-bet expression and IFN-γ production. miR-29b regulates T-bet and IFN-γ via a direct interaction with the 3' untranslated regions, and IFN-γ itself enhances miR-29b expression, establishing a novel regulatory feedback loop. miR-29b is increased in memory CD4(+) T cells from multiple sclerosis (MS) patients, which may reflect chronic Th1 inflammation. However, miR-29b levels decrease significantly upon T cell activation in MS patients, suggesting that this feedback loop is dysregulated in MS patients and may contribute to chronic inflammation. miR-29 thus serves as a novel regulator of Th1 differentiation, adding to the understanding of T cell-intrinsic regulatory mechanisms that maintain a balance between protective immunity and autoimmunity.

Macrophage migration inhibitory factor (MIF) is essential for inflammatory and neuropathic pain and enhances pain in response to stress

Stress and glucocorticoids exacerbate pain via undefined mechanisms. Macrophage migration inhibitory factor (MIF) is a constitutively expressed protein that is secreted to maintain immune function when glucocorticoids are elevated by trauma or stress. Here we show that MIF is essential for the development of neuropathic and inflammatory pain, and for stress-induced enhancement of neuropathic pain. Mif null mutant mice fail to develop pain-like behaviors in response to inflammatory stimuli or nerve injury. Pharmacological inhibition of MIF attenuates pain-like behaviors caused by nerve injury and prevents sensitization of these behaviors by stress. Conversely, injection of recombinant MIF into naïve mice produces dose-dependent mechanical sensitivity that is exacerbated by stress. MIF elicits pro-inflammatory signaling in microglia and activates sensory neurons, mechanisms that underlie pain. These data implicate MIF as a key regulator of pain and provide a mechanism whereby stressors exacerbate pain. MIF inhibitors warrant clinical investigation for the treatment of chronic pain.

Increased Th17 and regulatory T cell responses in EBV-induced gene 3-deficient mice lead to marginally enhanced development of autoimmune encephalomyelitis

EBV-induced gene 3 (EBI3)-encoded protein can form heterodimers with IL-27P28 and IL-12P35 to form IL-27 and IL-35. IL-27 and IL-35 may influence autoimmunity by inhibiting Th17 differentiation and facilitating the inhibitory roles of Foxp3(+) regulatory T (Treg) cells, respectively. In this study, we have evaluated the development of experimental autoimmune encephalomyelitis (EAE) in EBI3-deficient mice that lack both IL-27 and IL-35. We found that myelin oligodendrocyte glycoprotein peptide immunization resulted in marginally enhanced EAE development in EBI3-deficient C57BL6 and 2D2 TCR-transgenic mice. EBI3 deficiency resulted in significantly increased Th17 and Th1 responses in the CNS and increased T cell production of IL-2 and IL-17 in the peripheral lymphoid organs. EBI3-deficient and -sufficient 2D2 T cells had equal ability in inducing EAE in Rag1(-/-) mice; however, more severe disease was induced in EBI3(-/-)Rag1(-/-) mice than in Rag1(-/-) mice by 2D2 T cells. EBI3-deficient mice had increased numbers of CD4(+)Foxp3(+) Treg cells in peripheral lymphoid organs. More strikingly, EBI3-deficient Treg cells had more potent suppressive functions in vitro and in vivo. Thus, our data support an inhibitory role for EBI3 in Th17, Th1, IL-2, and Treg responses. Although these observations are consistent with the known functions of IL-27, the IL-35 contribution to the suppressive functions of Treg cells is not evident in this model. Increased Treg responses in EBI3(-/-) mice may explain why the EAE development is only modestly enhanced compared with wild-type mice.

Micro-RNA dysregulation in multiple sclerosis favours pro-inflammatory T-cell-mediated autoimmunity

Pro-inflammatory T cells mediate autoimmune demyelination in multiple sclerosis. However, the factors driving their development and multiple sclerosis susceptibility are incompletely understood. We investigated how micro-RNAs, newly described as post-transcriptional regulators of gene expression, contribute to pathogenic T-cell differentiation in multiple sclerosis. miR-128 and miR-27b were increased in naïve and miR-340 in memory CD4(+) T cells from patients with multiple sclerosis, inhibiting Th2 cell development and favouring pro-inflammatory Th1 responses. These effects were mediated by direct suppression of B lymphoma Mo-MLV insertion region 1 homolog (BMI1) and interleukin-4 (IL4) expression, resulting in decreased GATA3 levels, and a Th2 to Th1 cytokine shift. Gain-of-function experiments with these micro-RNAs enhanced the encephalitogenic potential of myelin-specific T cells in experimental autoimmune encephalomyelitis. In addition, treatment of multiple sclerosis patient T cells with oligonucleotide micro-RNA inhibitors led to the restoration of Th2 responses. These data illustrate the biological significance and therapeutic potential of these micro-RNAs in regulating T-cell phenotypes in multiple sclerosis.

Memory cells specific for myelin oligodendrocyte glycoprotein (MOG) govern the transfer of experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is an inflammatory disease of the CNS mediated by CD4(+) T cells directed against myelin antigens. Experimental autoimmune encephalomyelitis (EAE) is induced by immunization with myelin antigens like myelin oligodendrocyte glycoprotein (MOG). We have explored the transfer of EAE using MOG(35-55)-specific TCR transgenic (2D2) T cells. Unsorted 2D2 Th1 cells reliably transferred EAE. Further, we found that CD44(hi)CD62L(lo) effector/memory CD4(+) T cells are likely responsible for the disease transfer due to the up-regulation of CD44. Given the importance of MOG in MS pathogenesis, mechanistic insights into adoptively transferred EAE by MOG-specific Th1 cells could prove valuable in MS research.

Estriol generates tolerogenic dendritic cells in vivo that protect against autoimmunity

Chronic inflammation contributes to numerous diseases, and regulation of inflammation is crucial for disease control and resolution. Sex hormones have potent immunoregulatory abilities. Specifically, estrogen influences immune cells and inflammation, which contributes to the sexual dimorphism of autoimmunity and protection against disease seen during pregnancy in multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE). Although long thought to act primarily on T cells, recent evidence demonstrated that myeloid cells, such as dendritic cells (DCs), are essential in mediating estrogen's protective effects. Estriol (E3), a pregnancy-specific estrogen, has therapeutic efficacy in MS and EAE, and we evaluated whether E3 could act exclusively through DCs to protect against the inflammatory autoimmune disease EAE. Levels of activation markers (CD80 and CD86) and inhibitory costimulatory markers (PD-L1, PD-L2, B7-H3, and B7-H4) were increased in E3 DCs. E3 DCs had decreased proinflammatory IL-12, IL-23, and IL-6 mRNA expression, increased immunoregulatory IL-10 and TGF-β mRNA expression, and a decreased ratio of IL-12/IL-10 protein production. Importantly, transfer of E3 DCs to mice prior to active induction of EAE protected them from developing EAE through immune deviation to a Th2 response. This protection was apparent, even in the face of in vitro and in vivo inflammatory challenge. In summary, our results showed that E3 generates tolerogenic DCs, which protect against the inflammatory autoimmune disease EAE. Targeted generation of tolerogenic DCs with immunomodulatory therapeutics, such as E3, has potential applications in the treatment of numerous autoimmune and chronic inflammatory diseases.

A small-molecule inhibitor of macrophage migration inhibitory factor for the treatment of inflammatory disease

Multiple sclerosis (MS) is a chronic, debilitating disease of the central nervous system (CNS) characterized by demyelination and axon loss. The proinflammatory cytokine macrophage migration inhibitory factor (MIF) has been shown to be elevated in the cerebrospinal fluid of patients during relapses. The purpose of this study was to evaluate a new small-molecule inhibitor of MIF and its ability to reduce the severity of an animal model of MS, experimental autoimmune encephalomyelitis (EAE). We utilized 2 structurally related isoxazolines, which show in vitro inhibition of MIF tautomerase activity. We found that administration of an inhibitor of MIF to mice with established EAE immediately reduced the severity of clinical signs and expanded a population of regulatory T lymphocytes. We also noted that the inhibitor reduced relapses of disease in a relapsing/remitting model of EAE. An analysis of leukocyte migration into the brain revealed that administration of inhibitor reduced entry of these cells. No effects on inflammatory cytokine production or T-cell activation in the periphery were noted. From these studies, we conclude that a small-molecule inhibitor of MIF reduces the severity of EAE and prevents access of immune cells into the CNS, which could be of therapeutic relevance to MS.

Induction of pregnancy during established EAE halts progression of CNS autoimmune injury via pregnancy-specific serum factors

Multiple sclerosis (MS) is a demyelinating disease of the CNS involving T cell targeting of myelin antigens. During pregnancy, women with MS experience decreased relapses followed by a post partum disease flare. Using murine experimental autoimmune encephalomyelitis, we recapitulate pregnancy findings in both relapsing and progressive models. Pregnant mice produced less TNF-α, IL-17 and exhibited reduced CNS pathology relative to non-pregnant controls. Microparticles, called exosomes, shed into the blood during pregnancy were isolated and found to significantly suppress T cell activation relative to those from non-pregnant controls. These results demonstrate the immunosuppressive potential of pregnancy and serum-derived pregnancy exosomes.

MicroRNAs mediate autoimmune disease pathology (137.3)

Experimental autoimmune encephalomyelitis (EAE), studied as a model for multiple sclerosis (MS), is mediated by autoreactive CD4+ T cells. MicroRNAs (miRNAs) are a class of small, noncoding RNAs that regulate gene expression posttranscriptionally. Aberrant expression of miRNAs has been implicated in various disease processes. Recent evidence indicates that miRNAs are central to immune function and play a role in T cell responsiveness to antigen stimulation. We hypothesized that certain miRNAs would be differentially expressed in mice with EAE, and that these miRNAs represent critical mediators of autoimmune disease pathology. We utilized microarray technology, followed by PCR verification, to evaluate miRNA expression level at varying times during the EAE disease course. RNA was obtained from the lymph nodes and spleen during the acute and effector phases of EAE, and compared to animals receiving adjuvant alone. We found that several miRNAs are up- or downregulated during EAE and expression is temporally distinct. These data indicate that miRNAs represent a critical component of EAE pathology, and may be useful therapeutic targets or biomarkers in MS and other autoimmune diseases. Supported by NIH grants T32 GM068412, NS 48316 and AI 064320.

Macrophage migration inhibitory factor and the regulation of adhesion molecule expression on the blood brain barrier during experimental autoimmune encephalomyelitis (94.15)

Multiple sclerosis (MS) is a chronic inflammatory and demyelinating disease of the central nervous system (CNS). Cerebrospinal fluid (CSF) isolated from patients during relapse was found to contain greater levels of macrophage migration inhibitory factor (MIF) relative to samples collected during remission, thus suggesting a role for MIF in the pathogenesis of MS. We have demonstrated that upon induction of experimental autoimmune encephalomyelitis (EAE), mice deficient in MIF exhibit reduced clinical signs as well as fewer inflammatory infiltrates in the brain and spinal cord. MIF deficient mice, however, do not differ from wild type controls in the function of autoreactive lymphocytes in the periphery. These findings suggest that MIF is necessary for progression of EAE in the CNS, particularly at the level of the blood brain barrier (BBB). Mice treated with anti-MIF antibody show impaired migration of lymphocytes into the CNS and down-regulation of adhesion molecules on the BBB. Thus, we hypothesize that MIF is acting at the level of the BBB, regulating adhesion molecule expression and therefore access to the CNS. We are analyzing the expression of adhesion molecules, such as VCAM-1 and ICAM-1 in the brain and spinal cord of MIF deficient and small molecule inhibitor-treated mice. (Supported by NIH grant AI 064320 and National MS Society grant RG3272)

Exosomes are associated with pregnancy-induced suppression of experimental autoimmune encephalomyelitis (137.4)

Multiple sclerosis (MS) is a chronic disease of the central nervous system (CNS) characterized by inflammation, myelin damage, and axonal degeneration. MS disease relapses are markedly decreased during pregnancy with the greatest reduction in disease observed during the third trimester. We have studied pregnancy in the murine model of MS, experimental autoimmune encephalomyelitis (EAE). Disease severity is significantly reduced when pregnancy is induced during established EAE. We also observed a post-partum flare in disease scores, with EAE suppression only occurring during the gestation period. A serum factor has been implicated as the primary mediator of disease suppression. Exosomes found in peripheral blood are able to modulate the immune response by relaying molecular signals from their cell of origin to target cells bearing specific adhesion molecules. We have shown that pregnancy-associated exosomes are able to suppress antigen-specific T cell proliferation. Exosomes are hypothesized to dampen immune responses during pregnancy; thus, we examined exosomal proteins that are known to influence T cell activity such as Fas ligand, MHC II, TGF-β, IL-17, and IFN-γ. Harnessing the mechanism by which exosomes suppress immunity, and consequently EAE, can have remarkable implications for therapy development in MS. (Supported by NIH grants AI 064320 and T32 AI055411, and National MS Society grant RG3272)

A critical mediator of leukocyte extravasation during inflammatory disease (50.8)

Multiple sclerosis (MS) is a demyelinating neurological disease affecting more than 400,000 Americans. MS pathology involves activation of autoreactive lymphocytes and their migration across the blood-brain barrier (BBB) into the central nervous system (CNS). MS patients have a higher level of the ubiquitously expressed, proinflammatory cytokine MIF. Mice lacking MIF have fewer leukocytes in the CNS following induction of experimental autoimmune encephalomyelitis (EAE), an animal model for MS. We found using bone marrow chimeras that mice expressing MIF from myeloid cells had significantly more severe disease than MIF KO mice or mice expressing MIF only in non-myeloid cells (CDI±SD; 28.0±17.9 vs. 10.3±17.9 or 4.7±10.4). Using immunohistochemistry, we found more infiltrates in the CNS of mice expressing MIF from myeloid cells. We utilized a small molecule inhibitor of MIF to evaluate whether disruption of MIF activity could inhibit migration of leukocytes. Mice had reduced severity of EAE following inhibitor administration and reduced migration of leukocytes into the CNS. Other groups have shown that blocking MIF reduces expression of adhesion molecules on the BBB. Our data suggests that during inflammatory disease, MIF from myeloid cells is critical for leukocyte migration and an inhibitor of MIF reduces migration and subsequent clinical disease. (Supported by NIH grant AI 064320 and NMSS grant RG3272)

Pregnancy suppresses experimental autoimmune encephalomyelitis through immunoregulatory cytokine production

Women with multiple sclerosis (MS) often experience a decrease in relapse rate during pregnancy, most notably during the third trimester, with a flare of disease activity 3-6 mo postpartum. Studies in experimental autoimmune encephalomyelitis (EAE), an animal model for MS, have shown that pregnancy delays the onset and decreases the incidence of disease. We investigated the effect of pregnancy and the postpartum period in a remitting-relapsing model of murine EAE. When immunization occurs during pregnancy, mice show a reduction in the incidence of EAE as well as a decrease in clinical severity, while mice immunized during the postpartum period exhibit more severe disease. No differences in lymphocyte proliferation or expression of activation markers were noted when immunization occurred during pregnancy as compared with the nonpregnant controls. Mice immunized during pregnancy produced less TNF-alpha and IL-17, and showed an increased number of IL-10-secreting cells within the CD11b+, CD11c+, CD19+, and CD4+/CD25+ populations. No differences were noted in the production of IFN-gamma, IL-2, IL-4, and IL-5. These results suggest that when an Ag is introduced during pregnancy, an immunoregulatory rather than an immunosuppressive or Th2 environment predominates.

The Peyer's patch is a critical immunoregulatory site for mucosal tolerance in experimental autoimmune encephalomylelitis (EAE)

Expression of MCP-1 in the central nervous system (CNS) is associated with various neuroinflammatory diseases, including multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE). In this study, we found that MCP-1 was decreased in the CNS but increased in the gut following oral administration of myelin basic protein (MBP) correlating with protection from EAE. To study the trafficking and the fate of T cells during oral tolerance, MBP-specific TCR transgenic (Tg) CD4(+) T cells were labeled using 5,6-carboxy-succinimidyl-fluorescein-ester (CFSE) and transferred intravenously to syngeneic B10.PL recipients before feeding with either MBP or PBS. We observed that the CFSE-labeled T cells traffic to the peripheral lymphoid tissue and the Peyer's patches (PP). The labeled T cells proliferate in vivo in both the lymph node and the PP 48h after MBP feeding, but the cells are maintained in the PP longer than in the LN. CFSE-labeled cells in the PP have high levels of CD69 and Fas expression which is accompanied by increased apoptosis after MBP feeding. Our observations suggest that oral administration of autoantigen induces an elevation of MCP-1 in the gut, early T cell trafficking and activation in the periphery and the PP, followed by deletion of autoreactive T cells in the PP.

Induction of Golli-MBP expression in CNS macrophages during acute LPS-induced CNS inflammation and experimental autoimmune encephalomyelitis (EAE)

Microglia are the tissue macrophages of the CNS. Microglial activation coupled with macrophage infiltration is a common feature of many classic neurodegenerative disorders. The absence of cell-type specific markers has confounded and complicated the analysis of cell-type specific contributions toward the onset, progression, and remission of neurodegeneration. Molecular screens comparing gene expression in cultured microglia and macrophages identified Golli-myelin basic protein (MBP) as a candidate molecule enriched in peripheral macrophages. In situ hybridization analysis of LPS/IFNg and experimental autoimmune encephalomyelitis (EAE)–induced CNS inflammation revealed that only a subset of CNS macrophages express Golli-MBP. Interestingly, the location and morphology of Golli-MBP+ CNS macrophages differs between these two models of CNS inflammation. These data demonstrate the difficulties of extending in vitro observations to in vivo biology and concretely illustrate the complex heterogeneity of macrophage activation states present in region- and stage-specific phases of CNS inflammation. Taken altogether, these are consistent with the emerging picture that the phenotype of CNS macrophages is actively defined by their molecular interactions with the CNS microenvironment.

Disease-modifying capability of murine Flt3-ligand DCs in experimental autoimmune encephalomyelitis

Dendritic cells (DCs) bridge the innate and adaptive immune response, are uniquely capable of priming naïve T cells, and play a critical role in the initiation and regulation of autoimmune and immune-mediated disease. At present, in vivo expansion of DC populations is accomplished primarily through the administration of the recombinant human growth factor fms-like tyrosine kinase 3 ligand (hFL), and in vitro DCs are generated using cytokine cocktails containing GM-CSF +/- IL-4. Although hFL has traditionally been used in mice, differences in amino acid sequence and biological activity exist between murine FL (mFL) and hFL, and resultant DC populations differ in phenotype and immunoregulatory functional capabilities. This study developed and characterized mFL-generated DCs and determined the therapeutic capability of mFL DCs in the autoimmune disease experimental autoimmune encephalomyelitis (EAE). Our findings demonstrate that mFL and hFL expand splenic DCs equally in vivo but that mFL-expanded, splenic DCs more closely resemble normal, resting, splenic DCs. In addition, a novel method for generating mFL-derived bone marrow-derived DCs (BM-DCs) was developed, and comparison of mFL with hFL BM-DCs found mFL BM-DCs to be less mature (i.e., lower MHC Class II, CD80, and CD86) than hFL BM-DCs. These immature mFL DCs up-regulated costimulatory molecules in response to maturation stimuli LPS and TNF-alpha. Mature mFL BM-DCs were immunogenic and exacerbated the clinical disease course of EAE.

A novel approach to generating disease modifying dendritic cells (DCs) (129.13)

Dendritic cells (DCs) bridge the innate and adaptive immune responses and DC immunotherapy has shown promise in the treatment of transplantation, allergic and autoimmune diseases. One primary limitation in studying and utilizing DCs is their small numbers in vivo. While the growth factor Flt3-ligand (FL) is used to expand DCs in vivo, GM-CSF is predominantly used to generate DCs in vitro from bone marrow (BM-DC). The purpose of this study was to explore the use of murine FL (mFL), the mouse homologue of human FL, to generate DCs in vitro. In vivo (tumor-based) mFL delivery reliably expanded splenic DCs comparable to hFL In vitro BM-DCs generated with mFL were more similar to hFL than GM-CSF derived BM-DCs and appeared to be immature. Specifically, CD11c, CD11b and maturation markers CD80 and CD86 were lower in mFL and hFL versus GM-CSF BM-DCs. Maturation of mFL BM-DCs with TNF-α±LPS increased CD80, CD86 and CD40 expression. Transfer of matured mFL BM-DCs to mice prior to immunization with myelin oligodendrocyte glycoprotein (MOG35-55) significantly increased cumulative disease (26.79±10.12) and peak disease scores (3.07±1.16) compared to immature mFL BM-DCs (20.21 ±7.64 and 1.86±0.7, respectively). These results suggest that exposure to mFL in vitro is a novel method to generate large numbers of immature BM-DCs which can modulate the course of autoimmune disease.

(Support: NIH AI-43376, K01 R022198 and NMSS RG3272).

Late Pregnancy Serum Factors Suppress T Cell Activation in Experimental Autoimmune Encephalomyelitis (EAE) (42.14)

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the CNS thought to be due to an autoimmune response directed against myelin antigens. EAE is a commonly used animal model for MS and shares clinical, histopathologic and immunologic similarities with MS. Profound suppression of the MS and EAE relapse rate is observed during late pregnancy and is followed by a marked increase in disease severity postpartum. We have recently observed that histopathologic progression of EAE is diminished during late pregnancy and is exacerbated post partum. During EAE and late pregnancy, mice were found to have less mononuclear CNS infiltrates, demyelination and axon severing than virgin controls. The purpose of this study was to explore the hypothesis that decreased autoimmune disease during pregnancy is due to immunosuppressive factors present in the serum during late pregnancy. Female SJL/J mice were immunized for EAE using myelin proteolipid protein (PLP) 139–151. T cell proliferation assays were carried out using lymph node (LN) cells stimulated with PLP or anti-CD3 in the presence of 0–3% late pregnancy or virgin mouse sera. LN cells from age and gender matched naïve mice served as controls. Three percent late pregnancy serum suppressed both anti-CD3 and PLP stimulated T cell proliferation as compared to cells cultured with virgin mouse sera. These results demonstrate the broad suppressive potential of late pregnancy serum on T cell activation and may be responsible for amelioration of clinical signs of EAE during late pregnancy.

(Supported by NIH grants NS48316 and T32AI055411).

Immunomodulation of activated immune cells in experimental autoimmune encephalomyelitis (EAE) (42.7)

The relapse rate is profoundly decreased in female multiple sclerosis (MS) patients during pregnancy. We previously reported that experimental autoimmune encephalomyelitis (EAE), an animal model of MS, is markedly suppressed when disease is induced during late pregnancy. Disease induction during the post partum period is enhanced. In this study, we assess the effects of pregnancy on activated T cells by transferring neuroantigen activated transgenic T cells into pregnant syngeneic wild type recipients (B10.PL). Myelin basic protein (MBP) TCR transgenic (Tg) donor splenocytes are activated in vitro with MBP NAc1-11 for 96 hours. These CD4+CD25+Foxp3- donor cells elicited a strong proliferative response and an increase in Th1 cytokines. The activated T cells were transferred i.v. into pregnant recipients and non-pregnant controls. Control mice showed acute and relapsing EAE, while pregnant recipients showed significantly reduced cumulative disease scores. Furthermore, pregnancy inhibited T cell proliferation and increased the number of B cells post transfer. The role of regulatory/suppressive T cells and inhibitory molecules on antigen presenting cells (B cells and DCs) are under study for their involvement in pregnancy suppression of EAE

(Supported by NIH grant AI 43376).

A distinct role for PI3Kgamma in suppressing the development and progression of experimental autoimmune encephalomyelitis (EAE) (129.30)

Phosphoinositide 3-kinases (PI3K) are intracellular signaling proteins involved in cellular responses such as chemotaxis, proliferation and apoptosis. Selective inhibitors of the PI3Kγ-isoform have recently become available. This study explores the role of PI3Kγ in the development and progression of EAE. PI3Kγ +/+ (wt) and PI3Kγ −/− (ko) mice were immunized for EAE using myelin oligodendrocyte glycoprotein p35-55 (MOG) and assessed for clinical signs, CNS histopathology and T cell activation. WT mice showed a progressive disease course with elevations in inflammatory cytokines increased CNS mononuclear infiltrates. In contrast, ko mice exhibited a delayed onset and dramatically less severe EAE course characterized by decreased T cell activation and inflammatory cytokines (TNF-α, IFN-γ, IL-2, IL-12p40, IL-6, IL-17 and MCP-1). Male ko mice were significantly more protected than ko females. Adoptive transfer of MOG-activated T cells into ko recipients show that ko mice are resistant to passive disease induction. Interestingly, wt recipients of ko donors immunized for EAE were also protected. Furthermore, adoptive transfer of activated GFP+ T cells show marked decreased infiltration of GFP+ T cells into the CNS. Taken together, these findingssuggest that depletion of PI3Kγ results in a down-regulation of the inflammatoryresponse caused by impaired trafficking of cells critical to generation of the immune response.

(Supported by NIH grant AI 064320 and National MS Society Grant RG 3272).

Migration inhibitory factor modulates experimental autoimmune encephalomyelitis through a novel combination of suppressive mediators (131.34)

Multiple sclerosis (MS), an autoimmune disease of the central nervous system (CNS), is more prevalent in women than men. Recent studies suggest that the cytokine migration inhibitory factor (MIF) plays a role in the progression of MS and experimental autoimmune encephalomyelitis (EAE). We have shown that MIF−/− mice have decreased EAE severity relative to wt controls. Here, we evaluate the role of MIF in the context of known suppressive hormones. Serum levels of corticosterone (CORT) and testosterone (TEST) were measured prior to and following EAE induction in the presence and absence of MIF. Basal levels of TEST in MIF−/− mice were notably higher than controls; basal levels of CORT were low and similar between groups. Following EAE, there was little change in CORT and TEST in wt mice; however, TEST decreased and CORT increased in MIF−/− mice following immunization. To evaluate the role of TEST, we removed the testes of male MIF−/− mice and induced EAE. We found no difference in disease severity whether MIF−/− mice were gonadectomized or not; control mice had significantly more severe EAE in the absence of TEST. These findings suggest that CORT plays a larger role than TEST in disease progression, although both hormones appear to be influenced by MIF. Further study of the mechanism of MIF could lead to improved therapies for a variety of autoimmune diseases.

(Supported by NIH grant AI 064320 and National MS Society grant RG3272)

CD24 inhibits thymic deletion of myelin antigen-specific T cells (129.34)

CD24 is a glycosylphosphatidylinositol (GPI) anchored cell surface glycoprotein that is expressed in hematopoietic cells and cells of the central nervous system (CNS). We have previously shown that CD24 is required for the induction of experimental autoimmune encephalomyelitis (EAE), an experimental model of human disease multiple sclerosis. In CD24−/− mice, normal levels of myelin oligodendrocyte glycoprotein (MOG) specific T cell were primed, however these T cells were non-pathogenic. To understand this issue, we bred CD24−/− mice with 2D2 TCR transgenic mice, which bear TCR specific to MOG, and generated 2D2 TCR transgenic mice with or without CD24. Here we show that 2D2 TCR transgenic mice with CD24-deficiency (2D2/CD24−/−) have remarkably withered thymus. In peripheral lymphoid organs, transgenic T cells from 2D2/CD24−/− mice have an immature phenotype (CD4−CD8−), do not respond to MOG peptide stimulation, and fail to cause autoimmune inflammation in the CNS and optical nerves. In contrast, OT-2 TCR transgenic mice with CD24 deficiency (OT-2/CD24−/−), which bear TCR specific to chicken ovalbumin (OVA), have normal thymus and their peripheral T cells have a normal response to OVA peptide. These data suggest that CD24 inhibits thymic deletion of myelin antigen, but not foreign antigen-reactive T cells.

The Thymus Plays a Role in Oral Tolerance in Experimental Autoimmune Encephalomyelitis

The oral administration of myelin proteins has been used for the successful prevention and treatment of experimental autoimmune encephalomyelitis (EAE). We questioned whether the thymus was involved in oral tolerance. In this study, euthymic myelin basic protein (MBP) TCR transgenic mice are protected from EAE when fed MBP but are not protected when thymectomized. Similarly, in a cell transfer system, T cell responses to OVA measured in vivo were suppressed significantly only in the OVA-fed euthymic mice but not in the thymectomized mice. We observed that the absence of the thymus dramatically enhanced the Th1 response. We explored three alternatives to determine the role of the thymus in oral tolerance: 1) as a site for the induction of regulatory T cells; 2) a site for deletion of autoreactive T cells; or 3) a site for the dissemination of naive T cells. We found that Foxp3(+)CD4(+)CD25(+) T cells are increased in the periphery but not in the thymus after Ag feeding. These CD4(+)CD25(+) T cells also express glucocorticoid-induced TNFR and intracellular CTLA4 and suppress Ag-specific proliferation of CD4(+)CD25(-) cells in vitro. The thymus also plays a role in deletion of autoreactive T cells in the periphery following orally administered MBP. However, thymectomy does not result in homeostatic proliferation and the generation of memory cells in this system. Overall, the oral administration of MBP has a profound effect on systemic immune responses, mediated largely by the generation of regulatory T cells that act to prevent or suppress EAE.

Cutting Edge: Macrophage Migration Inhibitory Factor Is Necessary for Progression of Experimental Autoimmune Encephalomyelitis

Macrophage migration inhibitory factor (MIF) has been implicated in the pathogenesis of inflammatory and autoimmune diseases. The role of MIF in the progression of experimental autoimmune encephalomyelitis (EAE) was explored using MIF-/- mice. Wild-type mice showed a progressive disease course, whereas MIF-/- mice exhibited acute signs but no further progression of clinical disease. MIF-/- mice displayed markedly elevated corticosterone levels and significant decreases in the inflammatory cytokines TNF-alpha, IFN-gamma, IL-2, and IL-6 before, during, and after EAE onset. Taken together, these findings support that MIF is an important mediator of EAE progression through glucocorticoid antagonism and up-regulation of the inflammatory response.

Therapeutic peptidomimetic strategies for autoimmune diseases: costimulation blockade*

Cognate interactions between immune effector cells and antigen-presenting cells (APCs) govern immune responses. Specific signals occur between the T-cell receptor peptide and APCs and nonspecific signals between pairs of costimulatory molecules. Costimulation signals are required for full T-cell activation and are assumed to regulate T-cell responses as well as other aspects of the immune system. As new discoveries are made, it is becoming clear how important these costimulation interactions are for immune responses. Costimulation requirements for T-cell regulation have been extensively studied as a way to control many autoimmune diseases and downregulate inflammatory reactions. The CD28:B7 and the CD40:CD40L families of molecules are considered to be critical costimulatory molecules and have been studied extensively. Blocking the interaction between these molecules results in a state of immune unresponsiveness termed 'anergy'. Several different strategies for blockade of these interactions are explored including monoclonal antibodies (mAbs), Fab fragments, chimeric, and/or fusion proteins. We developed novel, immune-specific approaches that interfere with these interactions. Using experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis mediated by central nervous system (CNS)-specific T-cells, we developed a multi-targeted approach that utilizes peptides for blockade of costimulatory molecules. We designed blocking peptide mimics that retain the functional binding area of the parent protein while reducing the overall size and are thus capable of blocking signal transduction. In this paper, we review the role of costimulatory molecules in autoimmune diseases, two of the most well-studied costimulatory pathways (CD28/CTLA-4:B7 and CD40:CD40L), and the advantages of peptidomimetic approaches. We present data showing the ability of peptide mimics of costimulatory molecules to suppress autoimmune disease and propose a mechanism for disease suppression.

Regulation of autoreactive T cell function by oral tolerance to self-antigens

The oral administration of neuroantigens can suppress as well as treat autoimmune disease. Using EAE as a model system, we examined the antigen-presenting cell in oral tolerance. Expansion of dendritic cells (DCs) prior to or after disease is established facilitated oral tolerance. Transfer of oral antigen-loaded DCs resulted in protection from EAE by induction of IL-4 and IL-5 in recipient animals. LPS treatment of donors abrogated the ability of DCs to transfer protection from EAE, emphasizing the importance of the DC activation state. T cells exposed to orally administered antigen were monitored in TCR transgenic mice and found to undergo activation followed by deletion. The thymus plays a critical role in oral tolerance since thymectomized mice could not be tolerized. The thymus is postulated to be a site for deletion of autoreactive T cells or a site for generation of regulatory T cells.

The Thymus Plays a Role in Oral Tolerance Induction in Experimental Autoimmune Encephalomyelitis

Mice are protected from experimental autoimmune encephalomyelitis (EAE) when fed myelin basic protein (MBP). Thymectomized mice do not exhibit oral tolerance. We found evidence for two mechanisms to explain the role of the thymus in oral tolerance: a site for deletion of autoreactive T cells and a source of regulatory T cells.

Sex, MHC and complement C4 in autoimmune diseases

Autoimmune diseases are estimated to affect 10-50 million people in the United States, and untold millions worldwide. Nearly 80% of all people with autoimmune diseases are women, and a strong association of these diseases with MHC genes has been known for some time. However, very little is known about what causes autoimmune diseases or the factors that lead to disease recurrence. The sex-associated differences in multiple sclerosis (MS) and the mouse model of MS, experimental autoimmune encephalomyelitis (EAE), are associated with MHC genetic background, sex hormone levels and cytokine production. The implication of these factors has aided the identification of new autosomal genetic susceptibility loci. Complete deficiencies of early complement components are strongly associated with systemic lupus erythematosus (SLE) but the role of complement proteins in SLE is not yet clear. Recent data suggest that quantitative and qualitative diversities of the MHC-linked complement C4 among different ethnic groups can be important in the susceptibility and disease severity of SLE.

Sex differences in experimental autoimmune encephalomyelitis in multiple murine strains

Multiple sclerosis (MS) is more prevalent in women than men. We evaluated seven different mouse strains commonly used in the study of autoimmune diseases, for sex differences in the disease course of experimental autoimmune encephalomyelitis (EAE). Greater severity of EAE was observed in the female SJL immunized with two different peptides of myelin proteolipid protein (PLP) and myelin oligodendrocyte glycoprotein (MOG) as well as in the female ASW relative to males. Female NZW mice showed a greater incidence of EAE than males. However, male B10.PL and PL/J mice showed more severe disease than females. No sex differences were noted in the C57BL/6 or NOD strains.

Suppression of experimental autoimmune encephalomyelitis using peptide mimics of CD28

The B7:CD28/CTLA-4 costimulatory pathway plays a critical role in regulating the immune response and thus provides an ideal target for therapeutic manipulation of autoimmune disease. Previous studies have shown that blockade of CD28 signaling by mAbs can both prevent and exacerbate experimental autoimmune encephalomyelitis (EAE). In this study, we have designed two CD28 peptide mimics that selectively block B7:CD28 interactions. By surface plasmon resonance, both the end group-blocked CD28 peptide (EL-CD28) and its retro-inverso isomer (RI-CD28) compete effectively with the extracellular domain of CD28 for binding to B7-1. Both the CD28 peptide mimics inhibited expansion of encephalitogenic T cells in vitro. A single administration of EL-CD28 or RI-CD28 peptide significantly reduced disease severity in EAE. Importantly, we show that either CD28 peptide mimic administered during acute disease dramatically improved clinical signs of EAE, suppressing ongoing disease. The ratio of CD80:CD86 expression was significantly lower on CD4(+) and F4/80(+) spleen cells in CD28 peptide-treated mice. Peripheral deletion of Ag-specific CD4(+) T cells occurs following in vivo blockade of CD28 with synthetic CD28 peptides.

Peroxisome proliferator-activated receptor-gamma agonists prevent experimental autoimmune encephalomyelitis

The development of clinical symptoms in multiple sclerosis and its animal model experimental autoimmune encephalomyelitis (EAE) involves T-cell activation and migration into the central nervous system, production of glial-derived inflammatory molecules, and demyelination and axonal damage. Ligands of the peroxisome proliferator-activated receptor (PPAR) exert anti-inflammatory effects on glial cells, reduce proliferation and activation of T cells, and induce myelin gene expression. We demonstrate in two models of EAE that orally administered PPARgamma ligand pioglitazone reduced the incidence and severity of monophasic, chronic disease in C57BL/6 mice immunized with myelin oligodendrocyte glycoprotein peptide and of relapsing disease in B10.Pl mice immunized with myelin basic protein. Pioglitazone also reduced clinical signs when it was provided after disease onset. Clinical symptoms were reduced by two other PPARgamma agonists, suggesting a role for PPARgamma activation in protective effects. The suppression of clinical signs was paralleled by decreased lymphocyte infiltration, lessened demyelination, reduced chemokine and cytokine expression, and increased inhibitor of kappa B (IkB) expression in the brain. Pioglitazone also reduced the antigen-dependent interferon-gamma production from EAE-derived T cells. These results suggest that orally administered PPARgamma agonists could provide therapeutic benefit in demyelinating disease.

Differences between two strains of myelin basic protein (MBP) TCR transgenic mice: implications for tolerance induction

Experimental autoimmune encephalomyelitis (EAE) is mediated by CD4+ T cells which preferentially use the Vbeta8.2 TCR in response to myelin basic protein (MBP). Two strains of Tg mice (Valpha2.3/Vbeta8.2 and Valpha4/Vbeta8.2) have T cell receptors that recognize the NAc1-11 immunodominant epitope of MBP. We previously reported that oral administration of MBP protects both Valpha2.3/Vbeta8.2 and Valpha4/Vbeta8.2 mice from EAE; however, tolerance induction differs between strains and is dependent on the timing of oral antigen. Here we analyze the peripheral and gut-associated lymphoid tissue (GALT) environments of the two strains of Tg mice. Tg cells in the Peyer's patch (PP) but not the spleen of Valpha2.3/Vbeta8.2 mice demonstrate increased CD69 and decreased CD45RB relative to Valpha4/Vbeta8.2 mice. High levels of Th1 and Th2 cytokines, proliferative activity and CC chemokines (MCP-1) are observed in the periphery and GALT of Valpha2.3/Vbeta8.2 Tg mice. In contrast, more non-Tg CD4+ cells are seen in the PP of Valpha4/Vbeta8.2 mice. These studies suggest that activated Tg T cells and fewer potential regulatory cells in the PP of Valpha2.3/Vbeta8.2 Tg mice may influence oral tolerance.

Activation of Vbeta8 T cells affects spontaneous EAE in MBP TCR transgenic mice

Two strains of transgenic (Tg) mice (Valpha2.3/Vbeta8.2 and Valpha4/Vbeta8.2) have T cell receptors (TCR) that recognize the NAc1-11 immunodominant epitope of the myelin basic protein (MBP). Spontaneous experimental autoimmune encephalomyelitis (sEAE) readily develops in Valpha2.3/Vbeta8.2 mice. T cells in Valpha2.3/Vbeta8.2 mice demonstrate increased levels of CD69, CD44(high) and decreased CD45RB relative to Valpha4/Vbeta8.2 mice. Increased proliferative responses to MBP and high levels of TNF-alpha are seen in Valpha2.3/Vbeta8.2 mice. High IL-4 and TGF-beta production is observed in Valpha4/Vbeta8.2 mice. CC chemokines (macrophage inflammatory protein-1 alpha (MIP-1alpha), RANTES and monocyte chemotactic protein 1 (MCP-1)) are increased in the central nervous system (CNS) of Valpha2.3/Vbeta8.2 mice. Thus, activated Th1 cells in the periphery of Valpha2.3/Vbeta8.2 mice may traffic to the CNS in response to CC chemokines, influencing sEAE.

The role of the gut lymphoid tissue in induction of oral tolerance

The gut-associated lymphoid tissue (GALT) maintains a balance between immunological tolerance to dietary proteins and induction of active immune responses to pathogenic microorganisms. The oral administration of soluble protein antigens induces a state of systemic immunological unresponsiveness specific to the fed protein, termed oral tolerance. The two major mechanisms to explain oral tolerance are anergy/deletion of autoreactive lymphocytes and active suppression. This review will discuss the mechanisms of therapeutic oral tolerance in relation to events occurring at the site of antigen entry.

Alterations in immune cell phenotype and function after experimental spinal cord injury

Traumatic injury to the spinal cord initiates a cascade of inflammatory-mediated injury and repair processes within the nervous system. In parallel, spinal injury could influence peripheral mechanisms of host defense (e.g., wound healing, antibody production) by altering lymphocyte phenotype and function. The goal of this study was to evaluate the physiological impact of spinal contusion injury on phenotypic and functional indices of lymphocyte activation. A flow cytometric time-course analysis of lymphocytes isolated from lymph node and spleen revealed an increase in CD4+ and a decrease in CD8+ lymphocytes during the first week post injury. The functional potential of lymphocytes was also evaluated based on their ability to proliferate in the presence of a biologically relevant antigen (myelin basic protein, MBP) or a lymphocyte mitogen. The data revealed increased proliferation to MBP by 3 days postinjury in lymphocytes isolated from lymph node but not spleen. By 1 week postinjury, increased proliferation to mitogen was noted in both the lymph node and the spleen suggesting a general increase in lymphocyte reactivity during this time interval. Circulating corticosterone (CORT), an endogenous glucocorticoid with significant effects on lymphocyte phenotype and function, was elevated within 24 h after spinal cord injury (SCI) and remained above control levels throughout the duration of our studies (up to 1 month postinjury). The present data suggest injury-associated changes in immune cell phenotype and function paralleled by the activation of the hypothalamic-pituitary-adrenal (HPA) axis.

A retro-inverso peptide mimic of CD28 encompassing the MYPPPY motif adopts a polyproline type II helix and inhibits encephalitogenic T cells in vitro

Complete activation of T cells requires two signals: an Ag-specific signal delivered via the TCR by the peptide-MHC complex and a second costimulatory signal largely provided by B7:CD28/CTLA-4 interactions. Previous studies have shown that B7 blockade can either ameliorate experimental autoimmune encephalomyelitis by interfering with CD28 signaling or exacerbate the disease by concomitant blockade of CTLA-4 interaction. Therefore, we developed a functional CD28 mimic to selectively block B7:CD28 interactions. The design, synthesis, and structural and functional properties of the CD28 free peptide, the end group-blocked CD28 peptide, and its retro-inverso isomer are shown. The synthetic T cell-costimulatory receptor peptides fold into a polyproline type II helical structure commonly seen in regions of globular proteins involved in transient protein-protein interactions. The binding determinants of CD28 can be transferred onto a short peptide mimic of its ligand-binding region. The CD28 peptide mimics effectively block the expansion of encephalitogenic T cells in vitro suggesting the potential usefulness of the peptides for the treatment of autoimmune disease conditions requiring down-regulation of T cell responses.

Rapid depletion of peripheral antigen-specific T cells in TCR-transgenic mice after oral administration of myelin basic protein

In myelin basic protein (MBP)-specific TCR-transgenic (Tg) mice, peripheral T cells express the Valpha2.3/Vbeta8.2-Tg TCR, demonstrate vigorous proliferative responses to MBP in vitro, and can exhibit experimental autoimmune encephalomyelitis (EAE) within 5 days of pertussis toxin injection. We explored the effects of oral administration of MBP on the cellular trafficking of the MBP-specific TCR-Tg cells and the ability of oral MBP to protect Tg mice from EAE. Tg mice were fed MBP, OVA or vehicle and sacrificed at various times after feeding. An immediate and dramatic decrease in Valpha2.3/Vbeta8.2(+)-Tg cells was observed in the periphery within 1 h after feeding. By 3 days after feeding, the percentage of Tg cells increased to near control levels, but decreased again by 10 days. When MBP or vehicle-fed Tg mice were challenged for EAE at this point, disease was severe in the vehicle-fed mice and reduced in the MBP-fed mice over the 40-day observation period. In vitro studies revealed a biphasic pattern of MBP proliferative unresponsiveness and an induction of Th1 cytokines. Immunohistochemical staining showed that the number of Tg cells found in the intestinal lamina propria increased dramatically as the number of Tg cells in the periphery decreased. There was no apparent proliferation of Tg cells in the lamina propria, indicating that Tg cells trafficked there from the periphery. Taken together, these results suggest that T cell trafficking into the site of Ag deposition acts to protect the TCR-Tg mouse from EAE.

Neuropsychological performance in asymptomatic HIV infection

This study compared 74 human immunodeficiency virus (HIV)-negative and 131 HIV-positive asymptomatic homosexual or bisexual men on an extensive neuropsychological test battery. HIV-positive subjects' performance was significantly worse on verbal memory and psychomotor skills. The prevalence of mild but persistent neurobehavioral impairment in the HIV-positive group was approximately twice that in HIV-negative patients, consistently across several criteria for impairment. There was evidence that degree of neuropsychological impairment was related to patients' perceptions of dysfunction in daily life. Findings were not related to degree of depression or to medication effects. These data suggest that approximately 10% to 20% of HIV-positive asymptomatic men suffer mild neuropsychological impairment that influences their daily lives.

T-cell activation and receptor downmodulation precede deletion induced by mucosally administered antigen

The fate of antigen-specific T cells was characterized in myelin basic protein (MBP) T-cell receptor (TCR) transgenic (Tg) mice after oral administration of MBP. Peripheral Th cells are immediately activated in vivo, as indicated by upregulation of CD69 and increased cytokine responses (Th1 and Th2). Concurrently, surface TCR expression diminishes and internal TCR levels increase. When challenged for experimental autoimmune encephalomyelitis during TCR downmodulation, Tg mice are protected from disease. To characterize Th cells at later times after antigen feeding, it was necessary to prevent thymic release of naive Tg cells. Therefore, adult Tg mice were thymectomized before treatment. TCR expression returns in thymectomized Tg mice 3 days after MBP feeding and then ultimately declines in conjunction with MBP-specific proliferation and cytokine responses (Th1-type and Th2-type). The decline correlates with an increase in apoptosis. Collectively, these results demonstrate that a high dose of fed antigen induces early T-cell activation and TCR downmodulation, followed by an intermediate stage of anergy and subsequent deletion.