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.

Experimental autoimmune panencephalitis and uveoretinitis transferred to the Lewis rat by T lymphocytes specific for the S100 beta molecule, a calcium binding protein of astroglia.

The pathogenic potential of autoimmune T cell responses to nonmyelin autoantigens was investigated in the Lewis rat using the astrocyte-derived calcium binding protein S100 beta, as a model nonmyelin autoantigen. The Lewis rat mounts a vigorous RT1B1 (major histocompatibility complex class II) restricted autoimmune response to an immunodominant S100 beta epitope (amino acid residues 76-91). The adoptive transfer of S100 beta-specific T cell lines induced a severe inflammatory response in the nervous system, but only minimal neurological dysfunction in naive syngeneic recipients. The inability of S100 beta-specific T cell transfer to induce severe disease was associated with a decreased recruitment of ED1+ macrophages into the central nervous system (CNS) in comparison with that seen in severe experimental autoimmune encephalomyelitis (EAE) induced by the adoptive transfer of myelin basic protein (MBP)-specific T line cells. Moreover, unlike encephalitogenic MBP-specific T cell lines, S100 beta-specific T cell lines exhibited no cytotoxic activity in vitro. Histopathological analysis also revealed striking differences in the distribution of inflammatory lesions in MBP- and S100 beta-specific T cell-mediated disease. In contrast to the MBP paradigm, S100 beta-specific T cell transfer induces intense inflammation not only in the spinal cord, but throughout the entire CNS and also in the uvea and retina of the eye. In view of the distribution of lesions throughout the grey and white matter of the CNS we propose to term this new model experimental autoimmune panencephalomyelitis (EAP) to differentiate it from EAE. These experiments demonstrate for the first time that nonmyelin CNS autoantigens can initiate a pathogenic autoimmune T cell response, although the nature of the target autoantigen profoundly influences the clinical and histopathological characteristics of the resulting autoimmune disease. This is not simply a consequence of the distribution of the autoantigen, as both MBP and S100 beta are coexpressed in many areas of the CNS, but reflects differences in the capacity of different regions of the CNS to process and present specific autoantigens. This new model of T cell-mediated autoimmune CNS disease exhibits a number of similarities to multiple sclerosis (MS), such as its mild clinical course and the involvement of areas of the brain and eye, which are absent in myelin-mediated models of EAE. Nonmyelin autoantigens may therefore play an unexpectedly important role in the immunopathogenesis of inflammatory diseases of the CNS.

Late complications of immune deviation therapy in a nonhuman primate.

The administration of antigens in soluble form can induce antigen-specific immune tolerance and suppress experimental autoimmune diseases. In a marmoset model of multiple sclerosis induced by myelin oligodendrocyte glycoprotein (MOG), marmosets tolerized to MOG were protected against acute disease, but after tolerization treatment a lethal demyelinating disorder emerged. In these animals, MOG-specific T cell proliferative responses were transiently suppressed, cytokine production was shifted from a T helper type 1 (TH1) to a TH2 pattern, and titers of autoantibodies to MOG were enhanced. Thus, immune deviation can increase concentrations of pathogenic autoantibodies and in some circumstances exacerbate autoimmune disease.

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.

Antibody facilitation of multiple sclerosis-like lesions in a nonhuman primate.

In the human disease multiple sclerosis (MS), the immune mechanisms responsible for selective destruction of central nervous system myelin are unknown. In the common marmoset Callithrix jacchus, a unique demyelinating form of experimental allergic encephalomyelitis resembling MS can be induced by immunization with whole myelin. Here we show that the MS-like lesion can be reproduced by immunization against the extracellular domain of a single myelin protein, myelin/oligodendrocyte glycoprotein (MOG). By contrast, immunization against the quantitatively major myelin proteins myelin basic protein or proteolipid protein results in inflammation but little or no demyelination. Furthermore, in the presence of encephalitogenic (e.g., disease-inducing) T cells, the fully demyelinated lesion is reconstructed by systemic administration of IgG purified from whole myelin-, or MOG-immunized animals, and equally by a monoclonal antibody against MOG, but not by control IgG. Encephalitogenic T cells may contribute to the MS-like lesion through disruption of the blood-brain barrier that permits access of demyelinating antibody into the nervous system. The identification of MOG as a major target antigen for autoimmune demyelination in a nonhuman primate should facilitate development of specific immunotherapies for human MS.

Susceptibility and resistance to experimental allergic encephalomyelitis: relationship with hypothalamic-pituitary-adrenocortical axis responsiveness in the rat.

Susceptibility to experimental allergic encephalomyelitis (EAE) may be influenced by variations in the production of endogenous glucocorticoids. We investigated whether this concept is consistent across different genotypes and paradigms of EAE. In the major histocompatibility complex-disparate rat strains, Lewis (LEW), Brown Norway (BN), and Dark Agouti (DA), inflammatory and inflammatory-demyelinating variants of EAE were induced by immunization with myelin basic protein and myelin oligodendrocyte glycoprotein, respectively. We analyzed hormone production in EAE and after exposure to novel environment. DA and BN rats showed a robust hypothalamic-pituitary-adrenocortical (HPA) axis response to novelty stress and produced significantly higher ACTH and corticosterone plasma levels compared with LEW rats. However, HPA axis responsiveness was not associated with a generalized resistance to EAE, as both DA and LEW rats were susceptible to myelin basic protein-induced EAE. Moreover, both robust HPA responder strains, DA and the EAE-resistant BN rat, were highly susceptible to myelin oligodendrocyte glycoprotein-induced EAE. In animals of all strains, clinical disease was associated with significantly elevated plasma levels of corticosterone, and no differences in brain glucocorticoid-binding receptors were detected. Therefore, HPA axis characteristics are not a predictor of disease susceptibility in EAE.

Disease progression in chronic relapsing experimental allergic encephalomyelitis is associated with reduced inflammation-driven production of corticosterone.

In this study, we demonstrate that disruption of neuroendocrine signaling is a major factor driving disease progression in myelin oligodendrocyte glycoprotein-induced chronic relapsing experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis. Although the initial episode of chronic relapsing experimental autoimmune encephalomyelitis is associated with a robust hypothalamic-pituitary-adrenocortical axis response, we show that subsequent disease progression is associated with a selective desensitization of hypothalamic-pituitary-adrenocortical responsiveness to inflammatory mediators. Inflammatory activity in the central nervous system during relapse is therefore unable to produce an endogenous immunosuppressive corticosterone response, and disease progresses into an ultimately lethal phase. However, disease progression is inhibited if the circulating corticosterone level is maintained at levels seen during the initial phase of disease. The effect of hypothalamic-pituitary-adrenocortical axis desensitization on the clinical course of experimental autoimmune encephalomyelitis is aggravated by a marked reduction in proinflammatory cytokine synthesis in the central nervous system in the later stages of disease, reflecting an increasing involvement of antibody, rather than T cell-dependent effector mechanisms, in disease pathogenesis, with time. Thus, our data indicate that distinct immune-endocrine effects play a decisive role in determining disease progression in multiple sclerosis, a concept supported by reports that a subpopulation of multiple sclerosis patients shows evidence of hypothalamic-pituitary-adrenocortical axis desensitization.

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.

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.

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.

Antibody responses in chronic relapsing experimental allergic encephalomyelitis: correlation of serum demyelinating activity with antibody titre to the myelin/oligodendrocyte glycoprotein (MOG).

Antibody responses to the myelin/oligodendrocyte glycoprotein (MOG) and myelin basic protein (MBP) were determined in the sera of Hartley guinea pigs with chronic relapsing experimental allergic encephalomyelitis (CREAE) using an enzyme-linked immunoassay. The sera were also tested for in vivo demyelinating activity by infusion into the subarachnoid space of normal rats. In contrast to the MBP titres, the anti-MOG antibody titres showed good correlation with the in vivo demyelinating activity of the sera (r = 0.91, P less than 0.001). This result suggests that antibodies directed against MOG may be involved in the pathogenesis of demyelination in CREAE.

Identification of an encephalitogenic determinant of myelin proteolipid protein for the rabbit.

A late onset, demyelinating form of experimental allergic encephalomyelitis (EAE) was induced in New Zealand White rabbits following immunisation with a synthetic peptide representing the amino acid sequence 91-110 of bovine myelin proteolipid protein (PLP). Histologically, disease was associated with varying degrees of central nervous system (CNS) inflammation, which in six of seven animals was accompanied by axonal degeneration and secondary demyelination. Primary demyelination with axonal sparing was generally absent in this model of EAE. Immunohistochemical and immunoelectron microscopic analysis of CNS tissue indicate that B cell epitopes within this encephalitogenic PLP sequence are not exposed at the surface of the myelin sheath, but are sequestered within compact multilamellar myelin. Furthermore, no correlation was observed between the anti-PLP antibody titer induced by the peptide and either the clinical severity or histopathology of the disease. These observations suggest that the B cell response to epitopes within the PLP sequence 91-110 does not play a primary role in the immunopathogenesis of PLP-induced EAE.

The immune response to myelin proteolipid protein in the Lewis rat: identification of the immunodominant B cell epitope.

The polyclonal antibody response of the Lewis rat to bovine myelin proteolipid protein (PLP) has been investigated following immunisation with either the purified protein or bovine central nervous system myelin. In both situations, the carboxyl-terminal sequence of PLP was identified as the immunodominant domain of this protein and epitope mapping demonstrated that the carboxyl-terminal amino acid, phenylalanine276, was a critical requirement for antibody recognition of this epitope. This single epitope accounted for approximately 78% and 56% of the antibody response to PLP in rats immunised with PLP or bovine myelin, respectively. Polyclonal rat antibodies specific for this carboxyl terminal epitope of PLP were also obtained following immunisation with a synthetic 20 amino acid oligopeptide analogue of the carboxyl-terminal sequence of PLP. Western blotting demonstrated this antibody response was specific for the PLP and DM-20 components of mammalian central nervous system myelin. In contrast, no major PLP epitopes were detected within the PLP amino acid sequences 35-58 and 91-150, the other major hydrophilic domains of this protein.

Identification of a common idiotype on myelin oligodendrocyte glycoprotein-specific autoantibodies in chronic relapsing experimental allergic encephalomyelitis.

The myelin/oligodendrocyte glycoprotein (MOG) is a target antigen for autoantibody-mediated demyelination in chronic relapsing experimental allergic encephalomyelitis (CREAE) in the Strain 13 guinea pig. Anti-idiotypic antibodies directed against a demyelinating MOG-specific monoclonal antibody (8-18C5) have identified a cross-reactive idiotype in 10/10 CREAE sera. In nine of these sera inhibition studies demonstrated that this idiotype was at or in close proximity to the combination site of guinea pig anti-MOG autoantibodies. This cross-reactive anti-MOG idiotype may represent an important target for the anti-idiotypic regulation of demyelinating antibody responses in CREAE.

Induction of persistently demyelinated lesions in the rat following the repeated adoptive transfer of encephalitogenic T cells and demyelinating antibody.

A chronic relapsing model of demyelinating experimental allergic encephalomyelitis (EAE) was induced in Lewis rats by the repeated co-transfer of encephalitogenic, myelin basic protein (MBP)-specific T cells in combination with a demyelinating monoclonal antibody (mAb) specific for the myelin oligodendrocyte glycoprotein (MOG). In controls, repeated injections of 5 x 10(5) MBP-specific T cells at intervals of 18-21 days resulted in an increasing resistance to the induction of further episodes of EAE. However, intravenous injection of the mAb 4 days after each T cell transfer overcame this 'vaccination' effect and induced severe clinical relapses associated with an increasing and persistent neurological deficit. Histological examination revealed that four cycles of treatment with T cells and mAb were sufficient to result in the formation of large plaques of demyelination in the spinal cord that failed to undergo significant remyelination within 60 days of the final injection of mAb. These lesions consisted of a matrix of astrocytic scar tissue traversed by numerous naked axons. These observations demonstrate that the formation of large, persistently, demyelinated lesions in a T cell-mediated model of EAE in the Lewis rat is dependent on the presence of an appropriate anti-myelin autoantibody response.

Antibodies to myelin-oligodendrocyte glycoprotein in cerebrospinal fluid from patients with multiple sclerosis and controls.

Myelin-oligodendrocyte glycoprotein (MOG) has been implicated as a target for antibody-mediated immune attack in experimental autoimmune encephalomyelitis (EAE) which has been used extensively as an experimental model of multiple sclerosis (MS). We have screened cerebrospinal fluid (CSF) and plasma from 30 patients with MS, 30 with other neurological diseases (OND) and 30 with tension headache for anti-MOG antibodies of IgG isotype by enzyme-linked immunosorbent assay (ELISA). Such antibodies were detected in CSF from seven of the patients with MS, compared to two with OND and one with tension headache. No anti-MOG IgG antibodies were demonstrable in plasma. Antibody specificity was confirmed by Western blot immunostaining. Antibody levels were higher in MS compared to OND and tension headache. No correlation was observed between anti-MOG IgG antibodies and total IgG levels in CSF. The significance of anti-MOG antibodies demonstrated in MS CSF remains to be defined.

Induction of autoimmune reactions to myelin basic protein in measles virus encephalitis in Lewis rats.

Intracerebral inoculation of weanling Lewis rats with measles virus led to the development of subacute measles encephalomyelitis (SAME) 4-8 weeks after infection. The disease is characterized pathologically by an intense inflammatory infiltration within both the white and grey matter of the central nervous system (CNS) without apparent demyelination. Both during and after SAME splenic lymphocytes from these animals could be restimulated in vitro to proliferate in the presence of myelin base protein (MBP). MBP-specific class II MHC-restricted T cell lines were isolated from this cell population. They were shown to exhibit no cross-reactivity with measles virus and to induce experimental allergic encephalitis (EAE) in naive syngeneic recipients following adoptive transfer. The clinical and histopathological signs of this T cell-mediated disease were identical to that seen in classical T cell-mediated EAE. A humoral immune response to MBP was only detected in a limited number of those rats with SAME. These results indicate that autoimmune reactions to brain antigen can arise during measles virus infection which may contribute to the pathogenesis of measles virus-associated encephalomyelitis.

Encephalitogenic and neuritogenic T cell responses to the myelin-associated glycoprotein (MAG) in the Lewis rat.

Autoimmune responses to the myelin-associated glycoprotein (MAG) are implicated in the immunopathogenesis of both multiple sclerosis (MS) and certain peripheral neuropathies. In this study we demonstrate that T cell responses to defined epitopes of MAG mediate a pathological inflammatory response in the nervous system of the Lewis rat. Peptide-specific T cells were generated against four different MAG epitopes, three of which are common to both L- and S-isoforms of MAG (amino acid (a.a.) sequence: 20-34, 124-137, 354-377) whilst the fourth epitope (a.a. sequence: 570-582) is located in the C-terminal sequence of S-MAG. The adoptive transfer of T cells specific for these epitopes initiated a mild but dose-dependent inflammatory response in the central nervous system (CNS) of naive recipients. Clinical disease was only observed in those animals injected with T cells specific for the a.a. sequence 20-34 (MP1.1), which also initiated an inflammatory response in the peripheral nervous system (PNS). Co-transfer of MP1.1 (a.a. sequence 20-34)-specific T cells with the myelin oligodendrocyte glycoprotein (MOG)-specific monoclonal antibody 8-18C5 enhanced disease severity and induced widespread demyelination in the CNS. In contrast, co-transfer of T cells with the MAG-specific mAb 513 failed to induce demyelination, but had a moderate effect on the local inflammatory response. The ability of MAG to initiate an autoaggressive T cell response in the Lewis rat supports the concept that MAG-specific autoimmune responses may play a role in the pathogenesis of immune mediated diseases of the nervous system in man.

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.

T lymphocyte recognition sites on peripheral nerve myelin P0 protein.

Synthetic peptides corresponding to the extracellular and cytoplasmic domain of bovine (b) or rat (r) peripheral myelin P0 protein were used to establish a total of 50 short-term T cell lines (TCL) from blood of eight healthy subjects. Despite expressing different HLA-DR and HLA-DQ specificities, one or more TCL (range 1-16) specific for peptide bovine P0 19-38 could be isolated from the blood of each donor. Therefore, this peptide covers an immunodominant T cell recognition site in humans. However, when testing seven bP0-19-38-specific TCL derived from blood of two healthy subjects for recognition of the corresponding human P0 sequence, no TCL showed any proliferative response. Bovine P0-19-38 differs in only two amino acid residues from the human peptide. This observation stresses the necessity for using homologous antigens when screening for T cell-mediated autoreactivity to myelin antigens in humans. Unexpectedly, we failed to establish a single P0 peptide-specific TCL from blood of four patients with acute Guillain-Barré syndrome (GBS), in which P0 is considered a putative target autoantigen. As already suggested by others, this could indicate that T cell responses to P0 do not play a pathogenic role in all GBS cases. Alternatively, in these four patients neuritogenic P0-specific T lymphocytes may have been sequestrated to peripheral nerves.