Molecular mechanisms promoting progression of autoimmune myocarditis to dilated cardiomyopathy

Myocarditis is an inflammatory disease of the myocardium, described by infiltration of immune cells and cardiomyocyte necrosis. It is a major cause of sudden death in young adults. Patients often progress to a more severe form of the disease termed dilated cardiomyopathy (DCM). It is characterized by extensive fibrosis leading to impaired cardiac function. Immunosuppressive treatments with corticosteroids (CSs) have not been effective in preventing the disease. We hypothesized that macrophage migration inhibitory factor (MIF), being the only known pro-inflammatory cytokine induced by CSs may play a role in resistance to CSs. Also, MIF counter-regulates CS-mediated immunosuppression. Using the experimental autoimmune myocarditis (EAM) animal model, we observed that MIF−/− mice treated with Dexamethasone (Dex) were highly resistant to EAM and progression to DCM. Furthermore, from a translational approach, treatment using small molecule inhibitors of MIF combined with Dex recapitulated this phenotype in wild type mice. We observed that treated mice showed decreased expression of key chemokines and extracellular matrix molecules compared with controls, implicating these molecules in disease progression. Currently, we are investigating these molecules by selectively inhibiting them in order to understand their contribution to disease pathogenesis. We observed that inhibition of CCL2 after, although not prior to establishment of EAM attenuated progression to DCM. Thereby, suggesting that CCL2 is predominantly involved during the fibrotic phase aiding in progression as opposed to the induction phase of the disease. Besides a novel approach to prevent DCM, our studies may provide new insights into the mechanisms driving DCM.

Signaling via TNFR2 mediates CNS remyelination in EAE through regulation of oligodendrocyte progenitor cells

Tumor necrosis factor-alpha (TNF) is a pleiotropic inflammatory cytokine that has been associated with the pathogenesis of several autoimmune diseases, including multiple sclerosis (MS). Consequently, TNF-blocking drugs have been widely used to treat many inflammatory conditions and have proven highly effective. However, treatment of MS patients with anti-TNF drugs leads to disease exacerbation and severe demyelination. This effect has been specifically associated with lack of TNF signaling through its receptor, TNFR2. However, the underlying mechanisms are not fully understood. Experimental autoimmune encephalomyelitis (EAE) is the most common animal model used to study MS. Our lab has recently generated TNFR2−/− DR2b+/+ mice to study the role of TNFR2 signaling in EAE in the context of the HLA-DR2b (DRB1*1501), a haplotype strongly associated with MS. We found that these mice developed progressive EAE characterized by increased demyelinating lesions. Strikingly, this phenotype was not due to lack of TNFR2 expression in T cells, but rather was associated with a decreased numbers of oligodendrocyte progenitor cells (OPCs) in the CNS. Moreover, we demonstrated that TNFR2 signaling is critical for expression of chemokines in the CNS, suggesting its involvement in OPC function and recruitment. Our studies provide key insights into CNS repair and regulatory mechanisms controlled by TNF during inflammation, and this information may help develop novel therapeutic strategies.

Identification of Iguratimod as an Inhibitor of Macrophage Migration Inhibitory Factor (MIF) with Steroid-sparing Potential

Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine that has been implicated in a broad range of inflammatory and oncologic diseases. MIF is unique among cytokines in terms of its release profile and inflammatory role, notably as an endogenous counter-regulator of the anti-inflammatory effects of glucocorticoids. In addition, it exhibits a catalytic tautomerase activity amenable to the design of high affinity small molecule inhibitors. Although several classes of these compounds have been identified, biologic characterization of these molecules remains a topic of active investigation. In this study, we used in vitro LPS-driven assays to characterize representative molecules from several classes of MIF inhibitors. We determined that MIF inhibitors exhibit distinct profiles of anti-inflammatory activity, especially with regard to TNFα. We further investigated a molecule with relatively low anti-inflammatory activity, compound T-614 (also known as the anti-rheumatic drug iguratimod), and found that, in addition to exhibiting selective MIF inhibition in vitro and in vivo, iguratimod also has additive effects with glucocorticoids. Furthermore, we found that iguratimod synergizes with glucocorticoids in attenuating experimental autoimmune encephalitis, a model of multiple sclerosis. Our work identifies iguratimod as a valuable new candidate for drug repurposing to MIF-relevant diseases, including multiple sclerosis.

Identifying biomarkers for monitoring progression of multiple sclerosis

There are currently no reliable methods for assessing the progression of multiple sclerosis (MS) from the relapsing-remitting to the secondary progressive form. This gap in knowledge hinders the ability for therapeutic intervention and ultimately results in continued relapses and physiological deterioration. To begin to address the urgent need for biomarkers of progressive MS we investigated proteome changes over the disease course of progressive experimental autoimmune encephalomyelitis (EAE) in NOD mice as a preclinical model of the disease. Our lab has pioneered a novel high-throughput quantitative proteomic technique which we used to quantify expression levels of central nervous system (CNS) proteins over the course of monophasic EAE in C57.BL/6 mice. We utilized bioinformatics tools to prioritize key proteins whose expression level correlated specifically with the progressive phase of disease in the NOD EAE model. Importantly, we were able to detect corollary changes in these CNS-specific proteins in the serum, pointing to a minimally invasive means of monitoring disease progress and measuring drug efficacy. Our studies will provide a proof-of-concept for identifying homologous human biomarkers to guide treatment in individual patients. Furthermore, our results may provide insights into mechanisms that contribute to disease pathology and offer additional therapeutic targets for slowing the progression of MS.

ERK2 regulation of mitophagy is important for T cell activation

Critical signals necessary for T cell activation are transduced into the cell, in part, by the MAPK pathway, for which extracellular regulated kinase 2 (ERK2) is a key member. Upon activation, changes to mitochondria location and metabolism mediate T cell priming; however the signaling pathways that modulate mitochondria in T cells are largely unknown. A primary mechanism regulating mitochondria is a form of selective autophagy termed mitophagy. Importantly, ERK2 is required for mitophagy in other cell types and has been shown to co-localize at the autophagosome during formation. These data suggest that ERK2 may have a unique role regulating mitophagy in T cells. Notably, dysregulation of mitochondria in T cells can result in impaired immunity and has also been associated with autoimmune disease.

Here, we investigated the role of ERK2 for mitophagy in CD4+ T cells using a mouse model with T cell-specific deletion of ERK2. Our results show that Erk2−/− CD4+ T cells have impaired autophagosome formation and increased cell death upon activation, a phenotype consistent with mitophagy blockade. Further, we are working to identify key mitophagy proteins that are regulated by ERK2 and to characterize mitochondria signaling metabolites during T cell activation. By elucidating the signaling pathways that connect extracellular immune stimuli with mitochondria regulation, we will obtain important information that may lead to new therapeutic targets for T cell mediated diseases and dysfunction.

Pentraxin 3: an immune modulator of infection and useful marker for disease severity assessment in sepsis

The acute phase protein pentraxin 3 (PTX3) is a pattern recognition receptor involved in regulation of the host immune response. This relatively newly discovered member of the pentraxin superfamily elicits both immunostimulatory and immunoregulatory functions preventing autoimmune pathology and orchestrated clearance of pathogens through opsonization of damage- and pathogen-associated molecular patterns (DAMP/PAMP). Thus, PTX3 has been described as a possible evolutionary precursor to immunoglobulins. While shown to provide protection against specific bacterial and fungal pathogens, persistent elevation of PTX3 levels following initial onset of infection appear to predict poor patient outcome and may contribute to disease sequelae such as tissue damage and coagulopathy. Measurement of PTX3 following onset of sepsis may improve patient risk assessment and thus be useful in guiding subsequent therapeutic interventions including steroidal anti-inflammatory and altered antibiotic therapies. In this review, we summarize the role of PTX3 in inflammatory syndromes and its utility as a marker of sepsis disease severity.

Identifying biomarkers for monitoring disease progression in experimental autoimmune encephalomyelitis (THER7P.942)

Multiple sclerosis (MS) is the most common demyelinating neuroinflammatory disorder which afflicts over 400,000 Americans. Currently, determining clinical or sub-clinical disease progression in MS patients and development of novel treatments has been hampered by the lack of specific and sensitive laboratory tests. Recently, our lab has developed a technique called M2 proteomics, which is a rapid quantitative approach for identifying putative protein biomarkers and therapeutic targets of experimental autoimmune encephalomyelitis (EAE), a commonly used animal model for MS. Notably, we identified several putative-biomarkers which correlate with different stages of monophasic EAE. The objective of this study is to identify protein biomarkers of disease progression in a progressive EAE model using non-obese diabetic (NOD) mice. We hypothesize that during progressive EAE key central nervous system (CNS) disease-specific proteins will be released into blood and changes of these proteins can be used to determine disease progression. Using the progressive NOD EAE model, we determined the expression of putative CNS-specific protein biomarkers by immune assay in brain homogenate and serum longitudinally over the course of disease. We identified several CNS-specific potential biomarkers in serum that correlated with the progression of disease. The results of this study could help development of biomarkers for disease progression and testing of novel treatments for progressive MS.

MIF inhibition as novel treatment for autoimmune myocarditis and dilated cardiomyopathy (THER7P.956)

Myocarditis is an inflammatory disease of the myocardium and a major cause of sudden death in young adults. It is characterized by the presence of immune infiltrates in the myocardium and often progresses to dilated cardiomyopathy (DCM). Despite the inflammatory nature of this autoimmune disease, immunosuppressive treatments with glucocorticoids (GCs) such as dexamethasone (Dex) have not been very effective in preventing myocarditis and progression to DCM. In addition, some patients develop resistance to GCs. We hypothesized that macrophage migration inhibitory factor (MIF) may play a role in resistance to GCs, as it is the only known pro-inflammatory cytokine to be induced by GCs. Importantly, MIF counter-regulates GC-mediated immunosuppression. Using the experimental autoimmune myocarditis (EAM) model, we observed that MIF-/- mice treated with Dex were highly resistant to disease and progression to DCM. In addition, we observe lower expression of CCL3 mRNA in MIF-/- mice treated with Dex compared with wild-type mice during the onset of EAM, which indicates that MIF promotes recruitment of inflammatory cells to the myocardium. Our results suggest that therapeutic inhibition of MIF may increase the efficacy of GC treatment. This study will allow us to better understand the mechanism by which MIF affects treatment of myocarditis by inhibiting the therapeutic effects of GCs.

Identification of predictive protein biomarkers for treatment efficacy and clinical relapses of multiple sclerosis (THER7P.950)

Despite extensive research, MS remains a disease that lacks a definitive prognostic test to predict imminent disease relapses. Thus, patients may undergo years of unnecessary treatments. Additionally, current treatments for MS can produce dramatically different outcomes in different individuals and therefore there is a critical need to develop biomarkers for treatment efficacy and resistance. We have recently developed a novel quantitative proteomics method to measure changes in proteome expression over the course of experimental autoimmune encephalomyelitis (EAE). Our statistical analyses indicate a strong correlation to EAE severity and/or clinical-phase. Interestingly, we revealed characteristic CNS-specific protein expression waves prior to the onset of clinical symptoms. We are currently testing whether these protein expression waves allow us to predict the onset of clinical episodes and forecast the severity of the disease to guide treatment strategies. Additionally, we have identified changes in the CNS proteome that can be measured in serum during EAE that correlate with the therapeutic efficacy of glucocorticoid treatment. Our studies will provide proof-of-principle for developing homologous human biomarkers that may be useful to predict disease onset and treatment efficacy. Finally, the detected changes in the CNS proteome may provide insights into key mechanisms that contribute to the disease pathology and may be useful to develop new therapeutic targets for MS.

Erk2-deficiency impairs the effector function of mature CD4+ T cells (IRM15P.455)

Extracellular signal-regulated kinase 2 (Erk2) is required for CD4+T cell development and positive selection in the thymus, however the role of Erk2 in mature CD4+T cells is unknown. Erk2 is a key player of the mitogen activated protein kinase (MAPK) pathway which, in T cells, transduces crucial signals such as TCR engagement, CD28 co-stimulation, and cytokine binding. Upon activation, these signals are carefully coordinated to initiate gene expression programs, thus directing the expansion and differentiation of Ag-specific cells. The exquisite control of these signaling mechanisms is needed to maintain tolerance; dysregulation can result in inappropriate immune responses. In this study we used a mouse model with T cell-specific deletion of Erk2 to determine the role of Erk2 for CD4+T cell function. Our results show that increased numbers of Erk2∆CD4+T cells from naïve mice express markers for activation (CD25, CD44, and CD69). Further, Erk2∆CD4+T cells are able to survive and expand in vivo and proliferate upon IL-2, IL-7, and IL-15 cytokine stimulation. Importantly however, although the frequency and magnitude of Ag-specific Erk2∆CD4+T cell responses was comparable with controls upon antigen recall, secretion of IFN-g and IL-17 was significantly impaired. As CD4+T cells orchestrate immune responses primarily via cytokine production, our results suggest that Erk2 is required for CD4+T cell effector function.

Body fluid biomarkers in multiple sclerosis: how far we have come and how they could affect the clinic now and in the future

Multiple sclerosis (MS) is an autoimmune inflammatory disease of the central nervous system, which affects over 2.5 million people worldwide. Although MS has been extensively studied, many challenges still remain in regards to treatment, diagnosis and prognosis. Typically, prognosis and individual responses to treatment are evaluated by clinical tests such as the expanded disability status scale, MRI and presence of oligoclonal bands in the cerebrospinal fluid. However, none of these measures correlates strongly with treatment efficacy or disease progression across heterogeneous patient populations and subtypes of MS. Numerous studies over the past decades have attempted to identify sensitive and specific biomarkers for diagnosis, prognosis and treatment efficacy of MS. The objective of this article is to review and discuss the current literature on body fluid biomarkers in MS, including research on potential biomarker candidates in the areas of miRNA, mRNA, lipids and proteins.

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.

MOG transmembrane and cytoplasmic domains contain highly stimulatory T-cell epitopes in MS

Objective:

Recently, we reported that the 218 amino acid murine full-length myelin oligodendrocyte glycoprotein (MOG) contains novel T-cell epitopes p119-132, p181-195, and p186-200, located within its transmembrane and cytoplasmic domains, and that p119-132 is its immunodominant encephalitogenic T-cell epitope in mice. Here, we investigated whether the corresponding human MOG sequences contain T-cell epitopes in patients with multiple sclerosis (MS) and healthy controls (HC).

Methods:

Peripheral blood T cells from patients with MS and HC were examined for proliferation to MOG p119-130, p181-195, p186-200, and p35-55 by fluorescence-activated cell sorting analysis using carboxylfluorescein diacetate succinimidyl ester dilution assay. Intracellular production of proinflammatory cytokines was analyzed by flow cytometry.

Results:

MOG p119-130, p181-195, and p186-200 elicited significantly greater T-cell responses than p35-55 in patients with MS. T cells from patients with MS proliferated significantly more strongly to MOG p119-130 and p186-200 than did T cells from HC. Further, MOG p119-130–specific T cells exhibited Th17 polarization, suggesting this T-cell epitope may be relevant to MS pathogenesis.

Conclusions:

Transmembrane and cytoplasmic MOG domains contain potent T-cell epitopes in MS. Recognition of these determinants is important when evaluating T-cell responses to MOG in MS and may have implications for development of myelin antigen-based therapeutics.

Small molecule inhibitor of antigen binding and presentation by HLA-DR2b as a therapeutic strategy for the treatment of multiple sclerosis

The strong association of HLA-DR2b (DRB1*1501) with multiple sclerosis (MS) suggests this molecule as prime target for specific immunotherapy. Inhibition of HLA-DR2b-restricted myelin-specific T cells has the potential to selectively prevent CNS pathology mediated by these MHC molecules without undesired global immunosuppression. In this study, we report development of a highly selective small molecule inhibitor of peptide binding and presentation by HLA-DR2b. PV-267, the candidate molecule used in these studies, inhibited cytokine production and proliferation of myelin-specific HLA-DR2b-restricted T cells. PV-267 had no significant effect on T cell responses mediated by other MHC class II molecules, including HLA-DR1, -DR4, or -DR9. Importantly, PV-267 did not induce nonspecific immune activation of human PBMC. Lastly, PV-267 showed treatment efficacy both in preventing experimental autoimmune encephalomyelitis and in treating established disease. The results suggest that blocking the MS-associated HLA-DR2b allele with small molecule inhibitors may be a promising therapeutic strategy for the treatment of MS.

Human aquaporin 4281-300 is the immunodominant linear determinant in the context of HLA-DRB1*03:01: relevance for diagnosing and monitoring patients with neuromyelitis optica

OBJECTIVE To identify linear determinants of human aquaporin 4 (hAQP4) in the context of HLA-DRB1*03:01. DESIGN In this controlled study with humanized experimental animals, HLA-DRB1*03:01 transgenic mice were immunized with whole-protein hAQP4 emulsified in complete Freund adjuvant. To test T-cell responses, lymph node cells and splenocytes were cultured in vitro with synthetic peptides 20 amino acids long that overlap by 10 amino acids across the entirety of hAQP4. The frequency of interferon γ, interleukin (IL) 17, granulocyte-macrophage colony-stimulating factor, and IL-5-secreting CD4+ T cells was determined by the enzyme-linked immunosorbent sport assay. Quantitative immunofluorescence microscopy was performed to determine whether hAQP4281-300 inhibits the binding of anti-hAQP4 recombinant antibody to surface full-length hAQP4. SETTING Academic neuroimmunology laboratories. SUBJECTS Humanized HLA-DRB1*03:01+/+ H-2b-/- transgenic mice on a B10 background. RESULTS Peptide hAQP4281-300 generated a significantly (P <.01) greater TH1 and TH17 immune response than any of the other linear peptides screened. This 20mer peptide contains 2 dominant immunogenic 15mer peptides. hAQP4284-298 induced predominantly an IL-17 and granulocyte-macrophage colony-stimulating factor TH cell phenotype, whereas hAQP4285-299 resulted in a higher frequency of TH1 cells. hAQP4281-300 did not interfere with recombinant AQP4 autoantibody binding. CONCLUSIONS hAQP4281-330 is the dominant linear immunogenic determinant of hAQP4 in the context of HLA-DRB1*03:01. Within hAQP4281-330 are 2 dominant immunogenic determinants that induce differential TH phenotypes. hAQP4 determinants identified in this study can serve as diagnostic biomarkers in patients with neuromyelitis optica and may facilitate the monitoring of treatment responses to pharmacotherapies.

Evaluation of a HLA-DR2 Inhibitor for the Treatment of MS Using Human Cellular Immunologic Models (51.6)

Multiple sclerosis (MS) is the most common human neurological disease affecting approximately 400,000 Americans with no cure available. It is believed to be driven by autoimmune CD4+ T cell responses directed against myelin antigens in the CNS. CD4+ T cell activation and response require antigen presentation by MHC (HLA in human) class II molecules. The HLA class II allele HLA-DRB1*1501 (HLA-DR2) is highly associated with MS, therefore we tested the immunological properties and activity of PV-267, a small molecule DR2 inhibitor in vitro in human cellular immunologic models related to MS using flow cytometry analysis, human cytokine ELISPOT and Bio-Plex assays. In vitro studies of human PBMCs from MS patient or healthy control subjects and testing a myelin basic protein specific T cell line showed that: 1) DR2 inhibitors can inhibit myelin antigen-specific human T cell responses mediated via HLA-DR2; 2) inhibit the production of pro-inflammatory cytokines; 3) treatment with the inhibitors does not have undesired non-specific immune-activating effect on human PBMCs expressing either HLA-DR2 or other HLA-DR molecules. In sum, our preclinical study has established the immunologic efficacy and assessed the safety of DR2 inhibitors in vitro. The results provide a strong rationale for the application of MHC inhibitors for the treatment of MS and potentially other T cell-mediated autoimmune diseases based on the immunological efficacy and good safety profile.

Investigating the Role of ERK2 in Peripheral T cells Function Using a Novel Transgenic Mouse Model (47.13)

Extracellular signal Regulated Kinase 2 (ERK2) is an important Ser-Thr Kinase involved in MAPK pathway. It is indispensable for early T cell development and is also believed to play a role in T-cell specific antigen recognition signaling, cell proliferation, differentiation, migration and survival. However, it remains unclear how ERK2 regulates peripheral T cell function. Our studies focused on the impact and mechanism of ERK2 deficiency in peripheral T cell activation/function utilizing a mouse model with a conditional ERK2 knockout identified and confirmed by expression of a YFP reporter. Our gene knockout strategy relied on Cre recombinase driven by either distal Lck or inducible promoters. Using flow cytometry analysis/cell sorting and cytokine ELISPOT assay, we have found that T cell activation, survival and cytokine production were impaired in the absence of ERK2. Our results also indicate a role for ERK2 in cell survival in serum starvation and ionomycin/Ca2+ mediated apoptosis. The presented approach will allow us to further investigate the role of ERK2 in other peripheral T cell functions and potentially identify cellular signaling pathways that could be explored for the treatment of CD4+ T cell mediated autoimmune diseases such as MS.

Development of autoreactive CD8+ T cells in Aire-deficient mice (101.38)

Autoimmune regulator (Aire) regulates the transcription of a myriad of self antigens in the thymus, which is important for the process of central tolerance to eliminate autoreactive T cells and to prevent autoimmune pathology. Aire-deficient mice (aire-/-) have previously been shown to develop multi-organ autoimmune disorder. We were interested in investigating the role of Aire for autoreactive CD8+ T cells using aire-/-Ia-/- mice. We found that CD8+ T cells were increased in aire-/-Ia-/- mice as compare with their aire+/+ or heterozygous littermates. Furthermore, aire-/-Ia-/- mice showed significantly lower body weight as compared with their littermates. Immune infiltrates mainly composed of CD11c+ cells and CD8+ T cells were found in various tissues of aire-/-Ia-/- mice, especially in liver, lung, pancreas and stomach. Autoantibody was detected in the serum of aire-/-Ia-/- mice directed against gastric tissue and was determined to be predominantly IgM. Collectively, our study shows that autoreactive CD8+ T cells arise on the background of Aire-deficiency are capable of initiating and promoting autoimmunity in the absence of CD4+ T cells.

Antigen presentation in the CNS during EAE (100.26)

Experimental autoimmune encephalomyelitis (EAE) shares many similarities with the acute inflammatory episodes of human Multiple Sclerosis (MS) both clinically and histopathogically and has therefore been instrumental in defining the sequence of events that occur in MS. It is well established that CD4+ T cells specific for myelin antigen (Ag) can induce EAE in susceptible animals. Dendritic cells (DCs) and microglia are both capable of priming CD4+ T cells against myelin Ag via presentation by MHC class II molecules present on their cell surface. However, it has remained unclear precisely how infiltration of inflammatory cells into the CNS during EAE relates to the kinetics of myelin antigen uptake and presentation by specific APCs. In this study we have investigated which APCs are loaded with myelin antigen in the naïve brain as well as in the immunogenic context of EAE. Our results reveal that a low percentage of microglia are already pre-loaded with myelin Ag even in naïve mice and are capable of presenting Ag immediately for T cell activation following immunization. Several days after immunization a large influx of myelin-loaded DCs appears, coinciding with the onset of clinical disease. This data suggests that low-level presentation of myelin Ag by CNS-resident microglia may play a role in the induction phase of EAE, although the mechanism by which these cells have acquired Ag remains unresolved.

Macrophage migration inhibitory factor and its role in autoimmune diseases

After several decades of research into the macrophage migration inhibitory factor (MIF), its diverse actions in the immune system are yet to be fully revealed. What has become clear is that MIF plays an important role in both innate and adaptive immunity. However, while several pathways mediating the function of MIF in the immune system have been established, its role in pathogenic states such as autoimmune diseases has remained unresolved. MIF has been implicated in different autoimmune diseases, including rheumatoid arthritis, glomerulonephritis, and multiple sclerosis, but knowledge about the underlying cellular and molecular mechanisms is just emerging. However, overall it appears that the inhibition of its proinflammatory action is likely to be a successful new therapeutic strategy for some autoimmune diseases, possibly by reducing the need for steroids. As more aspects of the role of this cytokine in the pathogenesis of autoimmune diseases are elucidated, better strategies to target it therapeutically can be expected.

Autoreactive T cells promote post-traumatic healing in the central nervous system

In general, autoimmune responses are considered harmful to the host. In the best-defined model of autoimmune disease, murine experimental allergic encephalomyelitis (EAE), for example, brain-protein-specific autoimmune responses of both major classes, type-1 and type-2, have been implicated in causing brain pathology. We induced type-1 and type-2 autoimmunity to myelin oligodendrocyte protein (MOG) in C57.BL/6 mice. Instead of using pertussis toxin (PTX) to open the blood-brain barrier (BBB), which is the classic procedure, we set an aseptic cerebral injury (ACI) to see what the consequences of pre-primed, autoreactive type-1 and type-2 memory T cells gaining access to the brain in the course of sterile tissue injury would be. Neither of these autoimmune response types induced pathology; on the contrary, both accelerated re-vascularization and post-traumatic healing. The data suggest that induction of either type-1 or type-2 autoimmune responses is not inherently noxious to the host, but can have beneficial effects on tissue repair. Autoimmune pathology may develop only if molecules of microbial origin such as pertussis toxin additionally induce the "infectious nonself/danger" reaction in the antigen-presenting cells (APC) of the target organ itself.

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.

Revisiting tolerance induced by autoantigen in incomplete Freund's adjuvant

Injection of autoantigens in IFA has been one of the most effective ways of preventing experimental, T cell-mediated, autoimmune disease in mice. The mechanism that underlies this protection has, however, remained controversial, with clonal deletion, induction of suppressor cells or of type 2 immunity being implicated at one time or another. Using high resolution enzyme-linked immunospot (ELISPOT) analysis, we have revisited this paradigm. As models of autoimmunity against sequestered and readily accessible autoantigens, we studied experimental allergic encephalomyelitis, induced by myelin oligodendrocyte glycoprotein, proteolipid protein, myelin basic protein, and renal tubular Ag-induced interstitial nephritis. We showed that the injection of each of these Ags in IFA was immunogenic and CD4 memory cells producing IL-2, IL-4, and IL-5, but essentially no IFN-gamma. IgG1, but not IgG2a, autoantibodies were produced. The engaged T cells were not classic Th2 cells in that IL-4 and IL-5 were produced by different cells. The IFA-induced violation of self tolerance, including the deposition of specific autoantibodies in the respective target organs, occurred in the absence of detectable pathology. Exhaustion of the pool of naive precursor cells was shown to be one mechanism of the IFA-induced tolerance. In addition, while the IFA-primed T cells acted as suppressor cells, in that they adoptively transferred disease protection, they did not interfere with the emergence of a type 1 T cell response in the adoptive host. Both active and passive tolerance mechanisms, therefore, contribute to autoantigen:IFA-induced protection from autoimmune disease.