Nature, nurture, and microbes: The development of multiple sclerosis.

This paper argues that multiple sclerosis (MS) is the result of an autoimmune attack against components of the central nervous system (CNS). The effector cells involved in the pathogenic process are CNS-autoreactive T cells present in the healthy immune system in a resting state. Upon activation, these cells cross the blood-brain barrier and attack the CNS target tissue. Recent evidence indicates that autoimmune activation may happen in the intestine, following an interaction of bacterial components of the gut flora with local CNS autoreactive T cells. The consequences of this concept are discussed.

[Multiple sclerosis and microbiota. From genome to metagenome?]. / Multiple Sklerose und Mikrobiota. Vom Genom zum Metagenom?

The individual risk of contracting multiple sclerosis (MS) is determined by genetic predisposition as well as environmental factors. In monozygotic twins the concordance rate for MS is approximately 30 % indicating that environmental factors are even more important than genetic factors. Observations in a T-cell receptor-transgenic, spontaneous mouse model strongly point to an important contribution of the individual gut microbiome (microbiota). Mice maintained in a germ-free environment are completely protected from experimental autoimmune encephalomyelitis (EAE) in this model, whereas mice that are kept under normal conditions spontaneously develop a relapsing-remitting central nervous system (CNS) disease which is astoundingly similar to human MS. It appears that the autoimmune reaction against CNS tissue is "remotely controlled" by the gut microbiota. This may be explained by the facts that the microbiota influences the gut-associated lymphoid tissue (GALT) and, vice versa, the GALT regulates systemic immunity. The precise role of the microbiota in MS remains to be clarified. New methods of DNA sequencing and bioinformatics allow the analysis of very complex bacterial metagenomes. If individual microbial risk profiles can be identified this would provide completely new perspectives for the prophylaxis and therapy of MS.

Antibodies to MOG are transient in childhood acute disseminated encephalomyelitis.

OBJECTIVE: To study the longitudinal dynamics of anti-myelin oligodendrocyte glycoprotein (MOG) autoantibodies in childhood demyelinating diseases. METHODS: We addressed the kinetics of anti-MOG immunoglobulins in a prospective study comprising 77 pediatric patients. This was supplemented by a cross-sectional study analyzing 126 pediatric patients with acute demyelination and 62 adult patients with multiple sclerosis (MS). MOG-transfected cells were used for detection of antibodies by flow cytometry. RESULTS: Twenty-five children who were anti-MOG immunoglobulin (Ig) positive at disease onset were followed for up to 5 years. Anti-MOG antibodies rapidly and continuously declined in all 16 monophasic patients with acute disseminated encephalomyelitis and in one patient with clinically isolated syndrome. In contrast, in 6 of 8 patients (75%) eventually diagnosed with childhood MS, the antibodies to MOG persisted with fluctuations showing a second increase during an observation period of up to 5 years. Antibodies to MOG were mainly IgG 1 and their binding was largely blocked by pathogenic anti-MOG antibodies derived from a spontaneous animal model of autoimmune encephalitis. The cross-sectional part of our study elaborated that anti-MOG Ig was present in about 25% of children with acute demyelination, but in none of the pediatric or adult controls. Sera from 4/62 (6%) adult patients with MS had anti-MOG IgG at low levels. CONCLUSIONS: The persistence or disappearance of antibodies to MOG may have prognostic relevance for acute childhood demyelination.

Lessons from multiple sclerosis: models, concepts, observations.

Experimental autoimmune encephalomyelitis (EAE) is often termed "the" model of human multiple sclerosis (MS). This is, however, an oversimplification. MS is a multifaceted disorder, with no single experimental model representing the entire complexity of the human disease. On the other hand, EAE comes in numerous, distinct variants, which may reflect individual aspects of MS. This presentation reviews EAE variants and their usability as models for human MS. New transgenic models representing mechanisms determining spontaneous initiation, the course of central nervous system (CNS) autoimmunity, the distribution of lesions within the CNS and the cellular composition of the inflammatory infiltrate are discussed. Aspects of the early, inflammatory phase of MS plaque generation, in particular concerning the dynamics of immune cell invasion into the CNS, are also reviewed. Finally, the usability of EAE models for discovery and validation of MS drugs is discussed.

Blood-borne soluble protein antigen intensifies T cell activation in autoimmune CNS lesions and exacerbates clinical disease.

We explored the effect of i.v. soluble antigen on autoaggressive, myelin basic protein-specific effector T cells within their target organ during acute experimental autoimmune encephalomyelitis (EAE). Intravital two-photon imaging revealed that i.v. autoantigen reached the CNS and was taken up and processed by antigen-presenting cells within 30 min after injection. The exogenous autoantigen dramatically changed the motility and function of autoreactive effector T cells within the EAE lesions: T cells that had been cruising through the tissue slowed down and became tethered to local antigen-presenting cells within 1 h. One hour later, the effector T cells massively produced proinflammatory cytokines and up-regulated membranous activation markers. This strong activation of the T cells boosted CNS inflammation and aggravated clinical disease. Postactivated effector and resting memory T cells specific for a non-CNS antigen (ovalbumin) were recruited to EAE lesions and moved there without contacting antigen-presenting cells. These cells were similarly arrested and activated after i.v. infusion of ovalbumin, and they also exacerbated clinical disease. Our data are relevant for autoantigen-based therapies of autoimmune disorders. Further, the study indicates how brain unrelated antigens (microbial components) leaking into the chronically inflamed CNS through the bloodstream might trigger relapses in multiple sclerosis.

Breaking ignorance: the case of the brain.

Immunological self-tolerance is maintained through diverse mechanisms, including deletion of autoreactive immune cells following confrontation with autoantigen in the thymus or in the periphery and active suppression by regulatory cells. A third way to prevent autoimmunity is by hiding self tissues behind a tissue barrier impermeable for circulating immune cells. The latter mechanism has been held responsible for self-tolerance within the nervous tissue. Indeed, the nervous tissues enjoy a conditionally privileged immune status: they are normally unreachable for self-reactive T and B cells, they lack lymphatic drainage, and they are deficient in local antigen-presenting cells. Yet the immune system is by no means fully ignorant of the nervous structures. An ever-growing number of brain specific autoantigens is expressed within the thymus, which ensures an early confrontation with the unfolding T cell repertoire, and there is evidence that B cells also contact CNS-like structures outside of the brain. Then pathological processes such as neurodegeneration commonly lift the brain's immune privilege, shifting the local milieus from immune-hostile to immune-friendly. Finally, brain-reactive T cells, which abound in the healthy immune repertoire, but remain innocuous throughout life, can be activated and gain access to their target tissues. On their way, they take an ordered migration through peripheral lymphoid tissues and blood circulation, and undergo a profound reprogramming of their gene expression profile, which renders them fit to enter the nervous system and to interact with local cellule elements.

The neuroprotective effect of inflammation: implications for the therapy of multiple sclerosis.

Autoreactive T cells are a regular component of the healthy immune system. It has been proposed that some of these autoreactive T cells even might have a protective function. Recent studies support this notion by demonstrating that: a) myelin-autoreactive T cells show neuroprotective effects in vivo, and b) activated antigen-specific human T cells and other immune cells produce bioactive brain-derived neurotrophic factor (BDNF) and other neurotrophic factors in vitro. Furthermore, BDNF is expressed in different types of inflammatory cells in brain lesions of patients with acute disseminated leukoencephalopathy or multiple sclerosis. It seems plausible that the immune cell-mediated import of BDNF and other neurotrophic factors into the central nervous system has functional consequences and implications for the therapy of multiple sclerosis and other neuroimmunological diseases.

Transection of major histocompatibility complex class I-induced neurites by cytotoxic T lymphocytes.

Damage to neurites with transection of axons and spheroid formation is commonly noted in the central nervous system during viral and autoimmune diseases such as multiple sclerosis, but it remains open whether such changes are caused primarily by immune mechanisms or whether they are secondary to inflammation. The present experiments explored whether neurites can be directly attacked by cytotoxic T lymphocytes (CTLs). Cultured murine neurons induced by interferon-gamma and tetrodotoxin to express major histocompatibility complex class I were pulsed with a dominant peptide of the lymphochoriomeningitis virus envelope glycoprotein (GP33) and then confronted with GP33-specific CD8(+) CTLs. Within 3 hours the neurites developed cytoskeleton breaks with adjacent solitary neuritic spheroids, as documented by confocal examination of the cytoskeletal marker beta-tubulin III. At the same time cytoskeleton staining of the neuronal somata showed no damage. The CTLs selectively attacked neurites and induced segmental membrane disruption 5 to 30 minutes after the establishment of peptide-specific CTL-neurite contact, as directly visualized by live confocal imaging. Thus, major histocompatibility complex class I/peptide-restricted CD8(+) T lymphocytes can induce lesions to neurites, which might be responsible for axonal damage during neuroinflammatory diseases.

Fas ligand (CD95L) protects neurons against perforin-mediated T lymphocyte cytotoxicity.

Previous work showed that neurons of the CNS are protected against perforin-mediated T cell cytotoxicity, but are susceptible to Fas-mediated apoptosis. In this study, we report that Fas ligand (FasL) expression by neurons is involved in protection against perforin-mediated T cell cytotoxicity. Gene transcripts for FasL were identified in single murine hippocampal neurons by RT-PCR combined with patch clamp electrophysiology, and constitutive expression of FasL protein was confirmed in neurons by immunohistochemistry. Neurons derived from wild-type C57BL/6 (BL6) mice and mutant BL6.gld mice lacking functional FasL were confronted with allogeneic CTLs and continuously monitored in real time for changes in levels of intracellular calcium ([Ca(2+)](i)), an indicator of cytotoxic damage. Perforin-mediated plasma membrane lysis, characterized by rapid, massive [Ca(2+)](i) influx into the target cells within 0.5 h, was not detected in wild-type neurons. In striking contrast, FasL-deficient neurons showed rapid increase in [Ca(2+)](i) within 0.5 h, reflecting perforin-dependent cell lysis. FasL seems to protect neurons by blocking degranulation of CTLs, since CD3-induced release of cytotoxic granules was reduced by coapplication of Fas-specific Abs or rFasL.

Myelin antigen-specific CD8+ T cells are encephalitogenic and produce severe disease in C57BL/6 mice.

Encephalitogenic T cells that mediate experimental autoimmune encephalomyelitis (EAE) are commonly assumed to be exclusively CD4+, but formal proof is still lacking. In this study, we report that synthetic peptides 35-55 from myelin oligodendrocyte glycoprotein (pMOG(35-55)) consistently activate a high proportion of CD8+ alphabetaTCR+ T cells that are encephalitogenic in C57BL/6 (B6) mice. The encephalitogenic potential of CD8+ MOG-specific T cells was established by adoptive transfer of CD8-enriched MOG-specific T cells. These cells induced a much more severe and permanent disease than disease actively induced by immunization with pMOG(35-55). CNS lesions in pMOG(35-55) CD8+ T cell-induced EAE were progressive and more destructive. The CD8+ T cells were strongly pathogenic in syngeneic B6 and RAG-1(-/-) mice, but not in isogeneic beta2-microglobulin-deficient mice. MOG-specific CD8+ T cells could be repeatedly reisolated for up to 287 days from recipient B6 or RAG-1(-/-) mice in which disease was induced adoptively with <1 x 10(6) T cells sensitized to pMOG(35-55). It is postulated that MOG induces a relapsing and/or progressive pattern of EAE by eliciting a T cell response dominated by CD8+ autoreactive T cells. Such cells appear to have an enhanced tissue-damaging effect and persist in the animal for long periods.

Migratory activity and functional changes of green fluorescent effector cells before and during experimental autoimmune encephalomyelitis.

Homing behavior and function of autoimmune CD4+ T cells in vivo was analyzed before and during EAE, using MBP-specific T cells retrovirally engineered to express the gene of green fluorescent protein. The cells migrate from parathymic lymph nodes to blood and to the spleen. Preceding disease onset, large numbers of effector cells invade the CNS, with only negligible numbers left in the periphery. In early EAE, most (>90%) infiltrating CD4+ cells were effector cells. Migratory effector cells downregulate activation markers (CD25, OX-40) but upregulate several chemokine receptors and adsorb MHC class II on their membranes. Within the CNS, the effector cells are reactivated, with upregulated proinflammatory cytokines and downmodulated T cell receptor-associated structures, presumably reflecting autoantigen recognition in situ.

Immunological update on multiple sclerosis.

The present review of the recent literature focuses on antigen-specific immune reactions in multiple sclerosis. New techniques have allowed precise quantitative analysis of the antigen-receptor repertoire of infiltrating T cells in the multiple sclerosis brain. Novel candidate autoantigens, including B-cell autoantigens, have been identified. 'Humanized' animal models allow the functional characterization of human immune molecules in vivo. Finally, several therapeutic trials have recently assessed the clinical benefit of selective immunotherapies.

The fine specificity of the myelin oligodendrocyte glycoprotein autoantibody response in patients with multiple sclerosis and normal healthy controls.

Antibodies directed against the extracellular immunoglobulin (Ig)-like domain of the myelin oligodendrocyte glycoprotein (MOG(Igd)) mediate demyelination in experimental autoimmune encephalomyelitis (EAE) and are implicated in the immunopathogenesis of multiple sclerosis (MS). In this study we investigated the epitope specificity of MOG(Igd)-specific autoantibodies immunopurified from MS patients (n=17) and normal healthy controls (HD; n=9). ELISA, using a panel of synthetic MOG(Igd) peptides, revealed that the epitope specificity of this response was heterogeneous in both groups. The most frequently recognised epitopes were located in amino acid sequences (a.a.) 1-26 (13/17) and 63-87 (15/17) in MS patients, and 14-39 (6/9) and 63-87 (6/9) in HDs, but there was no association between MS and any particular peptide specificity. We therefore investigated the ability of the immunopurified antibodies to recognise native MOG(Igd) expressed on at the membrane surface by FACS. Unexpectedly, antibodies fulfilling this essential criterion for a demyelinating antibody response were detected only in one of the MS samples. These results indicate that the epitope specificity of the human B cell response to MOG is not only heterogeneous, but may only mediate demyelination in a limited subset of MS patients.

Anti-inflammatory activity of nerve growth factor in experimental autoimmune encephalomyelitis: inhibition of monocyte transendothelial migration.

In order to analyze a putative immunomodulatory effect of NGF in experimental autoimmune encephalomyelitis (EAE) of the Lewis rat, we transduced myelin basic protein (MBP)-specific CD4(+) T cells with a recombinant retrovirus encoding NGF. These T(MBP)NGF cells secreted high levels of NGF, along with an unaltered Th1-like cytokine pattern. Transfer studies showed that T(MBP)NGF cells were unable to mediate clinical EAE, when transferred alone, and, more important, they efficiently suppressed induction of clinical EAE by non-transduced MBP-specific T cells (T(MBP )cells). In contrast, NGF transduced ovalbumin-specific T cells, which secreted high NGF levels, did not affect EAE induction. Suppression of clinical EAE by T(MBP)NGF cells was associated with a general reduction of inflammatory CNS infiltrates, with a most pronounced decrease of the monocyte/macrophage component. Using a culture model of the endothelial blood-brain barrier (BBB), we found that NGF directly acts on blood-derived monocytes via the p75 NGF receptor, thus interfering with monocyte migration through the activated BBB endothelium. Our data establish NGF as an anti-inflammatory mediator interfering with T cell mediated autoimmune disease in the CNS. They further point to monocyte migration through blood vascular endothelium as one possible mechanism of NGF action.

Genetic models for CNS inflammation.

The use of transgenic technology to over-express or prevent expression of genes encoding molecules related to inflammation has allowed direct examination of their role in experimental disease. This article reviews transgenic and knockout models of CNS demyelinating disease, focusing primarily on the autoimmune disease multiple sclerosis, as well as conditions in which an inflammatory response makes a secondary contribution to tissue injury or repair, such as neurodegeneration, ischemia and trauma.

Development of myelin oligodendrocyte glycoprotein autoreactive transgenic B lymphocytes: receptor editing in vivo after encounter of a self-antigen distinct from myelin oligodendrocyte glycoprotein.

We explored mechanisms involved in B cell self-tolerance against brain autoantigens in a double-transgenic mouse model carrying the Ig H-chain (introduced by gene replacement) and/or the L-chain kappa (conventional transgenic) of the mAb 8.18C5, specific for the myelin oligodendrocyte glycoprotein (MOG). Previously, we demonstrated that B cells expressing solely the MOG-specific Ig H-chain differentiate without tolerogenic censure. We show now that double-transgenic (THkappa(mog)) B cells expressing transgenic Ig H- and L-chains are subjected to receptor editing. We show that in adult mice carrying both MOG-specific Ig H- and L-chains, the frequency of MOG-binding B cells is not higher than in mice expressing solely the transgenic Ig H-chain. In fact, in THkappa(mog) double-transgenic mice, the transgenic kappa(mog) L-chain was commonly replaced by endogenous L-chains, i.e., by receptor editing. In rearrangement-deficient RAG-2(-) mice, differentiation of THkappa(mog) B cells is blocked at an immature stage (defined by the B220(low)IgM(low)IgD(-) phenotype), reflecting interaction of the autoreactive B cells with a local self-determinant. The tolerogenic structure in the bone marrow is not classical MOG, because back-crossing THkappa(mog) mice into a MOG-deficient genetic background does not lead to an increase in the proportion of MOG-binding B cells. We propose that an as yet undefined self-Ag distinct from MOG cross-reacts with the THkappa(mog) B cell receptor and induces editing of the transgenic kappa(mog) L-chain in early immature B cells without affecting the pathogenic potential of the remaining MOG-specific B cells. This phenomenon represents a particular form of chain-specific split tolerance.