The N-terminal domain of the myelin oligodendrocyte glycoprotein (MOG) induces acute demyelinating experimental autoimmune encephalomyelitis in the Lewis rat

Candidate autoantigens in multiple sclerosis

Multiple sclerosis is an inflammatory demyelinating CNS disease of putatively autoimmune origin. Novel models of experimental autoimmune encephalomyelitis (EAE) have demonstrated that T cells specific for various myelin and even nonmyelin proteins are potentially encephalitogenic. The encephalitogenic T cell response directed against different CNS antigens not only determines the lesional topography of CNS inflammation but also the composition of the inflammatory infiltrates. The heterogeneity of the lesional distribution seen in EAE might therefore be useful for the understanding of the various clinical subtypes seen in MS. In this review the possible candidate autoantigens in MS are discussed with special regard to the human T cell and B cell responses against various myelin and nonmyelin proteins.

Epitope specificity of demyelinating monoclonal autoantibodies directed against the human myelin oligodendrocyte glycoprotein (MOG)

We describe the epitope specificity of a panel of ten demyelinating monoclonal antibodies (mAb) that recognise the extracellular immunoglobulin-like domain of human myelin oligodendrocyte glycoprotein (hMOG(lgd)). All the mAbs bind to the surface of MOG-transfected fibroblasts as assessed in vitro by FACS and immunocytochemistry but failed to recognise overlapping 15-mer MOG peptides when assessed by ELISA. However, increasing peptide length to 25 amino acids revealed that four mAbs recognised epitopes within the amino acid sequence 63-100 of human MOG. In contrast, a non-demyelinating MOG-specific mAb recognised MOG by both ELISA and Western blotting but failed to stain MOG transfected fibroblasts. These observations suggest that assays based on the use of MOG-transfected cell lines will differentiate between pathogenic and non-pathogenic MOG-specific antibody responses in experimental models and human diseases of the nervous system.

Effector pathways in immune mediated central nervous system demyelination

Multiple sclerosis is generally regarded to be a primarily T-cell driven disease. Recent evidence has refocused interest on antibodies. Adhesion molecules, matrix metalloproteinases, chemokines and cytokines, and nitric oxide and oxygen metabolites all participate in the amplification and effector stages of the disease.

Severity of symptoms and demyelination in MOG-induced EAE depends on TNFR1

The individual role of tumor necrosis factor receptor 1 (TNFR1) and TNFR2 signaling in experimental autoimmune encephalomeylitis (EAE) was investigated using mice lacking TNFR1 (TNFR1-/-), TNFR2 (TNFR2-/-) as well as double receptor (TNFR1/2-/-) and double ligand (TNF/LT alpha-/-) knockout mice. In wild-type (wt) mice immunized with myelin oligodendrocyte glycoprotein (MOG) peptide 35-55 the clinical course is characterized by an acute disease onset with peak disease scores and a consecutive chronic phase lasting up to 60 days. Compared to control mice, TNF/LT alpha-deficient mice showed a significant delay in disease onset and a remarkable reduction in demyelination which was, however, associated with increased inflammation. In TNFR1-/- and TNFR1/2-/- mice, the disease course was comparable to TNF/LT alpha-deficient mice but rather monophasic and less severe at late time points. Likewise only minimal spinal cord demyelination became apparent. In contrast, the course of EAE in TNFR2-/- mice was severe and associated with remarkable demyelination. Taken together these findings define TNFR1 as crucial mediator in MOG-induced EAE and suggest a protective role for TNFR2 signaling in the clinical course of EAE.

Neuronal expression of fractalkine in the presence and absence of inflammation

Fractalkine is the only as yet known member of a novel class of chemokines. Besides its novel Cys-X-X-X-Cys motif, fractalkine exhibits features which have not been described for any other member of the chemokine family, including its unusual size (397 amino acids human, 395 mouse) and the possession of a transmembrane anchor, from which a soluble form may be released by extracellular cleavage. This report demonstrates the abundant mRNA and fractalkine protein expression in neuronal cells. The neuronal expression of fractalkine mRNA is unaffected by experimentally induced inflammation of central nervous tissue.

Autoimmunity to myelin oligodendrocyte glycoprotein in rats mimics the spectrum of multiple sclerosis pathology

Multiple sclerosis is a chronic inflammatory disease characterized by perivenous inflammation and focal destruction of myelin. Many attempts have been undertaken previously to create animal models of chronic inflammatory demyelinating diseases through autoimmunity or virus infection. Recently, however, a new model of myelin oligodendrocyte glycoprotein (MOG) induced autoimmune encephalomyelitis became available, which, in a very standardized and predictable way, leads to chronic (relapsing or progressive) disease and widespread CNS demyelination. In the present study we actively induced MOG-experimental autoimmune encephalomyelitis (EAE) in different inbred rat strains using different immunization protocols. The pathology found in our models closely reflects the spectrum of multiple sclerosis (MS) pathology: Classical MS as well as variants such as optic neuritis, Devic's disease and Marburg's type of acute MS are mimicked in rats immunized with MOG antigen. Furthermore we demonstrate, that by using the proper strain/sensitization regime, subforms of MS such as for instance neuromyelitis optica can be reproducibly induced. Our study further supports the notion, that incidence and expression of the disease in this model, alike the situation in multiple sclerosis, is determined by genetic and environmental factors.

Increased reactivity to myelin oligodendrocyte glycoprotein peptides and epitope mapping in HLA DR2(15)+ multiple sclerosis

Multiple sclerosis (MS) is a central nervous system-specific inflammatory and demyelinating disease where a myelin-directed autoimmune response is thought to be pathogenetically relevant. Myelin oligodendrocyte glycoprotein (MOG) is a surface-exposed minor myelin component that is a prime candidate autoantigen. We have investigated peripheral blood lymphocyte responses to synthetic 15-26 amino acids long overlapping MOG peptides in 20 MS patients and 14 healthy controls with the MS-associated HLA haplotype DR2(15). There were significantly increased responses, in terms of numbers of cells secreting IFN-gamma detected by Elispot in response to several MOG-derived peptides in the MS patients, but not the healthy controls. MOG peptide 63-87 evoked the strongest response, and the stimulatory property of this peptide was confirmed in additional DR2(15)+ MS patients where a peptide concentration-dependent proliferative response, which was inhibited by the addition of anti-HLA class II antibodies, was observed. This is the first work detailing putative immunodominant T cell epitopes of MOG in DR2(15)+ MS patients.

MHC haplotype-dependent regulation of MOG-induced EAE in rats

Experimental autoimmune encephalomyelitis (EAE) induced in the rat by active immunization with myelin-oligodendrocyte-glycoprotein (MOG) is mediated by synergy between MOG-specific T cells and demyelinating MOG-specific antibody responses. The resulting disease is chronic and displays demyelinating central nervous system (CNS) pathology that closely resembles multiple sclerosis. We analyzed major histocompatibility complex (MHC) haplotype influences on this disease. The MHC haplotype does not exert an all-or-none effect on disease susceptibility. Rather, it determines the degree of disease susceptibility, recruitment of MOG-specific immunocompetent cells, clinical course, and CNS pathology in a hierarchical and allele-specific manner. Major haplotype-specific effects on MOG-EAE map to the MHC class II gene region, but this effect is modified by other MHC genes. In addition, non-MHC genes directly influence both disease and T cell functions, such as the secretion of IFN-gamma. Thus, in MOG-EAE, allelic MHC class II effects are graded, strongly modified by other MHC genes, and overcome by effects of non-MHC genes and environment.

Quantitative trait loci disposing for both experimental arthritis and encephalomyelitis in the DA rat; impact on severity of myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis and antibody isotype pattern

Quantitative trait loci (QTL) controlling inflammatory diseases with different organ specificity may hypothetically either be unique for one disease or shared among different diseases. We have investigated whether five non-MHC QTL controlling susceptibility to experimental arthritis in the DA rat also influence myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE) in an F2 intercross between inbred DA and PVG.RT1a rats. Two of the five chromosome regions affecting arthritis in the DA rat also regulate phenotypes of EAE. The DA allele at markers in Cia3 (collagen-induced arthritis QTL) on chromosome 4 is associated with more severe EAE and high levels of anti-MOG antibodies of the IgG2c subclass. Since production of antibodies of the IgG2c subclass may be stimulated by Th1 cells, and there is previous evidence that such cells promote EAE, it is possible that both of the studied phenotypes are controlled by the same gene or genes regulating Th1/Th2 cell differentiation. Furthermore, we show that Oia2 (oil-induced arthritis QTL) on chromosome 4 regulates levels of anti-MOG antibodies of the IgG1 subclass and of anti-MOG IgE, but that this gene region does not affect clinical disease severity in our study. Since production of IgE and IgG1 may be stimulated by Th2 cells, this QTL may also control Th1/Th2 bias. We conclude that Cia3 and Oia2 regulate MOG-induced EAE in rats. Furthermore, since both EAE and arthritis phenotypes co-localize to these gene regions, they may harbor genes which are key regulators of pathogenic immune responses.

B lymphocytes producing demyelinating autoantibodies: development and function in gene-targeted transgenic mice

We studied the cellular basis of self tolerance of B cells specific for brain autoantigens using transgenic mice engineered to produce high titers of autoantibodies against the myelin oligodendrocyte glycoprotein (MOG), a surface component of central nervous system myelin. We generated "knock-in" mice by replacing the germline JH locus with the rearranged immunoglobulin (Ig) H chain variable (V) gene of a pathogenic MOG-specific monoclonal antibody. In the transgenic mice, conventional B cells reach normal numbers in bone marrow and periphery and express exclusively transgenic H chains, resulting in high titers of MOG-specific serum Igs. Additionally, about one third of transgenic B cells bind MOG, thus demonstrating the absence of active tolerization. Furthermore, peritoneal B-1 lymphocytes are strongly depleted. Upon immunization with MOG, the mature transgenic B cell population undergoes normal differentiation to plasma cells secreting MOG-specific IgG antibodies, during which both Ig isotype switching and somatic mutation occur. In naive transgenic mice, the presence of this substantial autoreactive B cell population is benign, and the mice fail to develop either spontaneous neurological disease or pathological evidence of demyelination. However, the presence of the transgene both accelerates and exacerbates experimental autoimmune encephalitis, irrespective of the identity of the initial autoimmune insult.

Neuropathology in multiple sclerosis: new concepts

Multiple sclerosis lesions are characterized by inflammation, demyelination and a variable degree of axonal loss. The patterns of inflammation in MS lesions are compatible with a T-lymphocyte mediated immune reaction. The formation of demyelinated plaques, however, seem to require additional immunological mechanisms. In this review evidence is discussed for a pathogenetic role of demyelinating antibodies, toxic macrophage products, cytotoxic T-cells as well as metabolic disturbances of oligodendrocytes. It is suggested that the pathological heterogeneity regarding the patterns and extent of demyelination, remyelination and axonal loss may be the outcome of variable dominant immunopathogenetic mechanisms in different multiple sclerosis patients.

Serum antibodies against membranous labyrinth in patients with "idiopathic" bilateral vestibulopathy

To investigate the possibility of an autoimmune mechanism in idiopathic bilateral vestibulopathy (IBV), we screened patients' sera for antibodies against inner ear structures. IgG antibodies against membranous labyrinth (ampulla, semicircular canals, saccule and utricle) were detected in 8 of 12 patients by immunofluorescence on rat inner ear cryosections. All but one serum of 22 healthy controls and the sera of 6 patients with known autoimmune disorders showed only background staining. Low-titre anti-nuclear IgM antibodies were present in three control sera and one IBV serum. High-titre anti-nuclear IgM was found in a patient with lupus erythematosus and in one with scleroderma. Anti-nuclear IgM was not organ-specific. No human serum used contained detectable anti-vascular preformed antibodies. Cross-reactivity to sections of liver, kidney, cornea, brain and skeletal muscle was absent. Double-staining for IgG and F-actin, the primary constituent of hair cell cilia, did not show predominant Ig-coating of sensory hair cells. Immunosuppressive therapy in 3 IBV patients did not improve the disorder, probably owing to irreversible loss of sensory and neural structures. These data suggest that the bulk of anti-labyrinthine autoantibodies may be an epiphenomenon, yet a small subgroup of organ-specific autoantibodies may synergize with a cellular response in the development of vestibular lesions.

Insights into the aetiology and pathogenesis of multiple sclerosis

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system, and the most common neurological disease affecting young adults. Multiple sclerosis is a clinically heterogeneous disorder. It is believed to be an autoimmune disease, with cell-mediated and humoral responses directed against myelin proteins. This hypothesis largely comes from pathological parallels with an animal model, experimental autoimmune encephalomyelitis (EAE). Autoimmunity to myelin proteins in humans may be inadvertently triggered by microbes which have structural homologies with myelin antigens (molecular mimicry). As with other autoimmune diseases, susceptibility to MS is associated with certain MHC genes/haplotypes. Full genomic screening of mutiplex families has underscored the role for MHC genes as exerting moderate but the most significant effects in susceptibility. The primary target autoantigen in MS has yet to be definitively identified, but as well as the major myelin proteins, it is now clear that minor myelin components, such as myelin oligodendrocyte glycoprotein (MOG) may play a primary role in disease initiation. This review examines the current knowledge about the aetiology and pathogenesis of MS, and the important similarities with EAE. A better understanding of the molecular mechanisms of autoimmune pathology will provide the basis for more rational immunotherapies to treat MS.

Induction of chronic inflammatory arthropathy and mesenchymal tumors in rats infected with HTLV-I

To compare the pathogenicity of HTLV-I derived from patients with HTLV-I-associated myelopathy (HAM)/tropical spastic paraparesis (TSP) and that from patients with adult T-cell leukemia (ATL), neonatal WKA rats were inoculated with either an HTLV-I-infected T-cell line (Fuk line) newly established from a HAM/TSP patient or MT-2 derived from a patient with ATL. Of 38 rats, 34 developed mesenchymal tumors (89%) only after 14 months of age, irrespective of the cell lines used. The rats inoculated with the Fuk line developed severe arthritis (27%) and anti-type II collagen antibody (64%), and less frequently, paraparesis (7%). Those inoculated with MT-2 developed paraparesis (23%), but not arthritis. Cyclophosphamide (CY) administration to induce immunosuppression in the Fuk line-inoculated rats increased the frequency of paraparesis (70%), but decreased the frequency of tumors (20%). HTLV-I proviral DNA was found in the spinal cord, sciatic nerves, tumors, and joints, whereas pX mRNA was detected in the sciatic nerves and tumors, but not in the spinal cord and joints. As a result, HTLV-I is considered to facilitate development of both chronic inflammatory arthropathy associated with autoimmunity and mesenchymal tumors in rats by experimental infection, and its pathogenicity is likely to be greatly influenced by the host immune state.

Predominance of the autoimmune response to myelin oligodendrocyte glycoprotein (MOG) in multiple sclerosis: reactivity to the extracellular domain of MOG is directed against three main regions

Our previous analysis of the T cell reactivity to myelin antigens in a group of 24 patients with multiple sclerosis (MS) and 16 control individuals revealed that the autoimmune response to myelin oligodendrocyte glycoprotein (MOG) predominates in MS over that to myelin basic protein (MBP), proteolipid protein or myelin-associated glycoprotein, suggesting a prevalent role for the autoimmune response to MOG in the pathogenesis of MS. Using a recombinant human MOG (rhMOG) preparation corresponding to the extracellular immunoglobulin-like domain of the MOG molecule, we have now analyzed another group of 52 MS patients and 49 control individuals for reactivity of their peripheral blood lymphocytes (PBL) to rhMOG and to MBP concomitantly. Of the 52 MS patients tested 24 responded to MOG and 10 out of 49 responded to MBP, whereas only 5 MOG-reactive and 4 MBP-reactive control individuals were detected out of the 49 tested. These results are therefore highly confirmatory of the predominant reactivity to MOG in MS. The analysis of the primary proliferative response to 11 synthetic overlapping peptides (phMOG) spanning the extracellular domain of human MOG by PBL from 9 MS patients and 15 control individuals (9 healthy controls and 6 patients with neurological diseases other than MS) further supports a prevalent role for the autoimmune response to MOG in MS, as only 1 of the 15 controls tested showed reactivity to any of the phMOG, whilst 5 out of the 9 patients studied reacted to at least 1 of the phMOG. PBL from 10 MS patients, and from 4 controls, were selected in vitro with each of the phMOG. Of the 10 patients studied 7 reacted to at least 1 phMOG upon secondary stimulation and the reactivity was mostly directed to epitopes localized within three main regions (amino acids 1-22, 34-56 and 64-96), as was observed for the primary response of PBL. The predominant response to MOG of PBL from MS patients as demonstrated in two separate studies using native MOG and rhMOG as antigens, and the high incidence of reactivity of these PBL compared to the lack of response to phMOG by control PBL, emphasize the relevance of MOG in MS pathogenesis and support a primary role for the autoimmune T cell response to MOG in disease development.

Glycoproteins of myelin sheaths

A growing number of glycoproteins have been identified and characterized in myelin and myelin-forming cells. In addition to the major P0 glycoprotein of compact PNS myelin and the myelin-associated glycoprotein (MAG) in the periaxonal membranes of myelin-forming oligodendrocytes and Schwann cells, the list now includes peripheral myelin protein-22 (PMP-22), a 170 kDa glycoprotein associated with PNS myelin and Schwann cells (P170k/SAG), Schwann cell myelin protein (SMP), myelin/oligodendrocyte glycoprotein (MOG), and oligodendrocyte-myelin glycoprotein (OMgp). Many of these glycoproteins are members of the immunoglobulin superfamily and express the adhesion-related HNK-1 carbohydrate epitope. This review summarizes recent findings concerning the structure and function of these glycoproteins of myelin sheaths with emphasis on the physiological roles of oligosaccharide moieties.

Animal models of demyelination

Demyelination is a pathological feature that is characteristic of many diseases of the central nervous system (CNS) including multiple sclerosis (MS), sub-acute sclerosing panencephalomyelitis (SSPE), metachromatic leukodystrophy and Pelizaeus-Merzbacher disease. While demyelination is a pathological end-point that is common to all of these diseases, the cellular and molecular mechanisms responsible for this pathology are very different . These range from genetic defects that affect lipid metabolism in the leukodystrophies, cytopathic effects of viral infection in SSPE to the action of immunological effector mechanisms in MS and the viral encephalopathies. Irrespective of the initial cause of myelin degradation, many of these disorders are associated with some degree of CNS inflammation, as indicated by the local activation of microglia, recruitment of macrophages or the intrathecal synthesis of immunoglobulin. Many of these phenomena are now being duplicated in animal models, providing not only new insights into the pathogenesis of human demyelinating diseases , but also unexpected interrelationships between the immune response in the CNS and the pathogenesis of diseases such as Alzheimers disease and HIV encephalopathy. Autoimmune mediated models of inflammatory demyelinating CNS disease have proved particularly valuable in this respect as they allow the effects of defined immune effector mechanisms to be studied in the absence of CNS infection.