A new family of transcripts of the myelin basic protein gene: expression in brain and in immune system

Molecular and Diffusion Tensor Imaging Biomarkers of Traumatic Brain Injury: Principles for Investigation and Integration

The last 20 years have seen the advent of new technologies that enhance the diagnosis and prognosis of traumatic brain injury (TBI). There is recognition that TBI affects the brain beyond initial injury, in some cases inciting a progressive neuropathology that leads to chronic impairments. Medical researchers are now searching for biomarkers to detect and monitor this condition. Perhaps the most promising developments are in the biomolecular and neuroimaging domains. Molecular assays can identify proteins indicative of neuronal injury and/or degeneration. Diffusion imaging now allows sensitive evaluations of the brain's cellular microstructure. As the pace of discovery accelerates, it is important to survey the research landscape and identify promising avenues of investigation. In this review, we discuss the potential of molecular and diffusion tensor imaging (DTI) biomarkers in TBI research. Integration of these technologies could advance models of disease prognosis, ultimately improving care. To date, however, few studies have explored relationships between molecular and DTI variables in patients with TBI. Here, we provide a short primer on each technology, review the latest research, and discuss how these biomarkers may be incorporated in future studies.

Identification of Candidate Signature Genes and Key Regulators Associated With Trypanotolerance in the Sheko Breed

African animal trypanosomiasis (AAT) is caused by a protozoan parasite that affects the health of livestock. Livestock production in Ethiopia is severely hampered by AAT and various controlling measures were not successful to eradicate the disease. AAT affects the indigenous breeds in varying degrees. However, the Sheko breed shows better trypanotolerance than other breeds. The tolerance attributes of Sheko are believed to be associated with its taurine genetic background but the genetic controls of these tolerance attributes of Sheko are not well understood. In order to investigate the level of taurine background in the genome, we compare the genome of Sheko with that of 11 other African breeds. We find that Sheko has an admixed genome composed of taurine and indicine ancestries. We apply three methods: (i) The integrated haplotype score (iHS), (ii) the standardized log ratio of integrated site specific extended haplotype homozygosity between populations (Rsb), and (iii) the composite likelihood ratio (CLR) method to discover selective sweeps in the Sheko genome. We identify 99 genomic regions harboring 364 signature genes in Sheko. Out of the signature genes, 15 genes are selected based on their biological importance described in the literature. We also identify 13 overrepresented pathways and 10 master regulators in Sheko using the TRANSPATH database in the geneXplain platform. Most of the pathways are related with oxidative stress responses indicating a possible selection response against the induction of oxidative stress following trypanosomiasis infection in Sheko. Furthermore, we present for the first time the importance of master regulators involved in trypanotolerance not only for the Sheko breed but also in the context of cattle genomics. Our finding shows that the master regulator Caspase is a key protease which plays a major role for the emergence of adaptive immunity in harmony with the other master regulators. These results suggest that designing and implementing genetic intervention strategies is necessary to improve the performance of susceptible animals. Moreover, the master regulatory analysis suggests potential candidate therapeutic targets for the development of new drugs for trypanosomiasis treatment.

Experimental Autoimmune Encephalomyelitis (EAE) as Animal Models of Multiple Sclerosis (MS)

Multiple sclerosis (MS) is a multifocal demyelinating disease of the central nervous system (CNS) leading to the progressive destruction of the myelin sheath surrounding axons. It can present with variable clinical and pathological manifestations, which might reflect the involvement of distinct pathogenic processes. Although the mechanisms leading to the development of the disease are not fully understood, numerous evidences indicate that MS is an autoimmune disease, the initiation and progression of which are dependent on an autoimmune response against myelin antigens. In addition, genetic susceptibility and environmental triggers likely contribute to the initiation of the disease. At this time, there is no cure for MS, but several disease-modifying therapies (DMTs) are available to control and slow down disease progression. A good number of these DMTs were identified and tested using animal models of MS referred to as experimental autoimmune encephalomyelitis (EAE). In this review, we will recapitulate the characteristics of EAE models and discuss how they help shed light on MS pathogenesis and help test new treatments for MS patients.

Relapsing-remitting central nervous system autoimmunity mediated by GFAP-specific CD8 T cells

Multiple sclerosis (MS) is an inflammatory disease of the CNS that causes the demyelination of nerve cells and destroys oligodendrocytes, neurons, and axons. Historically, MS has been thought to be a CD4 T cell-mediated autoimmune disease of CNS white matter. However, recent studies identified CD8 T cell infiltrates and gray matter lesions in MS patients. These findings suggest that CD8 T cells and CNS Ags other than myelin proteins may be involved during the MS disease process. In this article, we show that CD8 T cells reactive to glial fibrillary acidic protein (GFAP), a protein expressed in astrocytes, can avoid tolerance mechanisms and, depending upon the T cell-triggering event, drive unique aspects of inflammatory CNS autoimmunity. In GFAP-specific CD8 TCR-transgenic (BG1) mice, tissue resident memory-like CD8 T cells spontaneously infiltrate the gray matter and white matter of the CNS, resulting in a relapsing-remitting CNS autoimmunity. The frequency, severity, and remissions from spontaneous disease are controlled by the presence of polyclonal B cells. In contrast, a viral trigger induces GFAP-specific CD8 T effector cells to exclusively target the meninges and vascular/perivascular space of the gray and white matter of the brain, causing a rapid, acute CNS disease. These findings demonstrate that the type of CD8 T cell-triggering event can determine the presentation of distinct CNS autoimmune disease pathologies.

Hematopoietic progenitors express myelin basic protein and ensheath axons in Shiverer brain

Oligodendroglia are cells of the central nervous system (CNS) that form myelin sheath, which insulates neuronal axons. Neuropathologies of the CNS include dysmyelination of axons in multiple sclerosis and CNS trauma. Cell replacement is a promising but largely untested therapy for dysmyelination. Shiverer mouse, a genetic mutant that does not synthesize full-length myelin basic protein (MBP), a critical prerequisite protein in CNS myelin sheath formation, provides an unequivocal model for determining the potential of stem cells to become oligodendroglia. We demonstrate that adult wild-type mouse bone marrow stem cells can express MBP and ensheath axons when transplanted into Shiverer brain.

Adult hematopoietic progenitors are multipotent in chimeric mice

Embryonic stem cells (ESCs) and adult somatic cells, induced to pluripotency (iPSCs), can differentiate into multiple cell lineages. We previously reported that adult mammalian bone marrow contains a sub-population of CD34+ cells that express genes of ESCs and genes required to generate iPSCs. They also express lineage genes of the three embryonic germ layers. Are these CD34+ cells multipotent? Here, CD34+ bone marrow stem cells from adult male ROSA mice, which carry two markers: the β-galactosidase gene and the male Y chromosome, were transplanted into blastocysts of wildtype mice. Each female ROSA chimera generated had a distinct pattern of male-derived organs expressing β-galactosidase; e.g., ectodermal brain, dorsal root ganglia and skin; mesodermal heart, bone and bone marrow; and endodermal pancreas, intestine, and liver. Thus, adult mammals carry cells that appear to exhibit a developmental potential reminiscent of ESCs and iPSCs suggesting they could be used for cell replacement therapy.

Pharmacotherapeuetic Options for the Treatment of Multiple Sclerosis

Multiple sclerosis is the most common progressive and disabling neurological condition in young adults. Neuro-inflammation is an early and persistent change and forms the basis of most pharmacotherapy for this disease. Immunomodulatory drugs are mainly biologies (β-interferons, a four amino acid peptide, and a monoclonal antibody to a cell adhesion molecule on the blood-CNS barrier) that either attenuate the inflammatory response or block the movement of immune cells into the CNS. They reduce the rate of relapse, but have little or no effect on the progression of disability. The market landscape for MS drugs is in the midst of major change because the patent life of many of these medicines will soon expire, which will lead to the emergence of biosimilars. In addition, new small molecule immunomodulatory and palliative drugs have entered the market, with more in the pipeline; a number of monoclonal antibodies and other immunomodulatory drugs are also in clinical development.

Immune tolerance in multiple sclerosis

Multiple sclerosis is believed to be mediated by T cells specific for myelin antigens that circulate harmlessly in the periphery of healthy individuals until they are erroneously activated by an environmental stimulus. Upon activation, the T cells enter the central nervous system and orchestrate an immune response against myelin. To understand the initial steps in the pathogenesis of multiple sclerosis, it is important to identify the mechanisms that maintain T-cell tolerance to myelin antigens and to understand how some myelin-specific T cells escape tolerance and what conditions lead to their activation. Central tolerance strongly shapes the peripheral repertoire of myelin-specific T cells, as most myelin-specific T cells are eliminated by clonal deletion in the thymus. Self-reactive T cells that escape central tolerance are generally capable only of low-avidity interactions with antigen-presenting cells. Despite the low avidity of these interactions, peripheral tolerance mechanisms are required to prevent spontaneous autoimmunity. Multiple peripheral tolerance mechanisms for myelin-specific T cells have been identified, the most important of which appears to be regulatory T cells. While most studies have focused on CD4(+) myelin-specific T cells, interesting differences in tolerance mechanisms and the conditions that abrogate these mechanisms have recently been described for CD8(+) myelin-specific T cells.

Minireview: expression and function of golli protein in immune system

In this minireview, the author briefly reviews the development of our understanding on the immunological function of golli proteins. In the immune system, in addition to serving as autoantigens, golli proteins have been recently found to regulate T-cell activation directly, thus modulating EAE induction. The evidence that golli proteins function as signal molecules is summarized.

Autoimmune CD4+ T cell memory: lifelong persistence of encephalitogenic T cell clones in healthy immune repertoires

We embedded green fluorescent CD4(+) T cells specific for myelin basic protein (MBP) (T(MBP-GFP) cells) in the immune system of syngeneic neonatal rats. These cells persisted in the animals for the entire observation period spanning >2 years without affecting the health of the hosts. They maintained a memory phenotype with low levels of L-selectin and CD45RC, but high CD44. Although persisting in low numbers (0.01-0.1% of lymph node cells) they were sufficient to raise susceptibility toward clinical autoimmune disease. Immunization with MBP in IFA induced CNS inflammation and overt clinical disease in animals carrying neonatally transferred T(MBP-GFP) cells, but not in controls. The onset of the clinical disease coincided with mass infiltration of T(MBP-GFP) cells into the CNS. In the periphery, following the amplification phase a rapid contraction of the T cell population was observed. However, elevated numbers of fully reactive T(MBP-GFP) cells remained in the peripheral immune system after acute experimental autoimmune encephalomyelitis mediating reimmunization-induced disease relapses.

CD8+ T cells maintain tolerance to myelin basic protein by 'epitope theft'

Myelin basic protein-specific CD8(+) T cells can induce central nervous system autoimmunity; however, immune tolerance prevents these autoreactive cells from causing disease. To define the mechanisms that mediate tolerance, we developed two T cell receptor-transgenic mouse lines with different affinities for the H-2K(k)-restricted myelin basic protein epitope consisting of amino acids 79-87 (MBP(79-87)). We observed both thymic deletion and peripheral tolerance in the lower-affinity T cells. The higher-affinity T cells, however, showed no evidence of tolerance induction and were able to prevent tolerance of the lower-affinity T cells by removing H-2K(k)-MBP(79-87) complexes from antigen-presenting cells without proliferating. This form of immune regulation could limit responses of self-reactive T cells that escape other tolerance mechanisms.

Immune tolerance to myelin proteins

Multiple sclerosis (MS) is a demyelinating disorder of the central nervous system. It is believed to be an autoimmune disease arising from a breakdown of immune tolerance in T cells specific for myelin antigens. The heterogeneity in clinical signs and pathology observed in MS patients suggests a complex pathogenesis in which the specificity of the pathogenic T cells and the tolerance mechanisms that are compromised vary among individual patients. In this review, we summarize some of the features of the diverse immune pathology observed in MS and the animal models used to study this disease. We then describe the current state of knowledge regarding the expression of the major myelin protein antigens believed to be targeted in MS and the mechanisms of immune tolerance that operate on T cells that recognize these antigens.

Identification and characterisation of a cDNA encoding a 17-kDa isoform of rat myelin basic protein

The myelin basic proteins (MBPs) are the major proteins of the myelin membrane. Multiple MBP mRNAs and protein isoforms are generated by alternative RNA splicing. Here we describe the isolation and characterisation of a cDNA clone encoding a 17-kDa MBP isoform from the rat (Rattus norvegicus). The isoform is a 158-amino acid protein consisting of exons 1, 3, 4, 6 and 7 of the MBP gene. RT-PCR analysis of brain mRNA showed that transcripts encoding the 17-kDa isoform were expressed at higher levels early in post-natal development, up to 7 days post-partum.

The myelin basic protein gene is expressed in differentiated blood cell lineages and in hemopoietic progenitors

Myelin basic proteins (MBP) are major constituents of the myelin sheath of oligodendrocytes and Schwann cells in the central nervous system and the peripheral nervous system, respectively. We previously showed that MBP-related transcripts are present in the bone marrow and the immune system. These mRNAs are transcribed from a region called 0', consisting of three exons, located upstream of the classical MBP exons; these three exons belong to the long MBP gene otherwise called "Golli-MBP." The most abundant of these mRNAs, now called HMBP (hemopoietic MBP), encompasses the sequence encoded by the region 0' plus exon 1 and part of intron 1 of the classic MBP gene. Antisera to recombinant HMBP proteins are immunoreactive with proteins of about 26-28 kDa in brain, thymus, and spleen. This report demonstrates that HMBP proteins are present in the vast majority (>95%) of thymic T cells, which express the corresponding transcripts, as do mature T cells from lymph nodes and spleen. HMBP mRNAs and proteins are also manifest in the majority of spleen B lymphocytes and in B cell lines. In addition to lymphoid cells, HMBP proteins are in all types of myeloid lineage cells, i.e., macrophages, dendritic cells, and granulocytes, as well as in megakaryocytes and erythroblasts. Finally, HMBP proteins are present in CD34+ bone marrow cells, and, furthermore, in highly proliferative cultures, these CD34+ cells express HMBP RNAs and proteins. Thus, MBP gene products are present both in the nervous system and in the entire hemopoietic system.

Expression of Golli proteins in adult human brain and multiple sclerosis lesions

It has been suggested that Golli proteins, structurally related to myelin basic proteins (MBPs), have a role in autoimmune processes. We studied the expression of these proteins in multiple sclerosis (MS) and determined that the number of Golli-immunoreactive (ir) cells was significantly higher around lesions of chronic MS than in control white matter. Golli proteins were expressed in the adult oligodendrocyte precursor cells (OPCs), activated microglia/macrophages, and some demyelinated axons around MS lesions. Their expression in adult OPCs indicates remyelination attempts, whereas the expression in the subpopulation of microglia/macrophages suggests roles in the immune processes of MS. In addition, Golli proteins may be markers of axonal transection, which is characteristic for MS.

Developmental changes and localization of mouse brain serine proteinase mRNA and protein in mouse brain

Serine proteases are known to be involved in neural development and various functions in the central nervous system. Mouse brain serine proteinase (mBSP) is expressed almost exclusively in the mouse brain and it has been characterized at the molecular and biochemical levels. In this study, we analyzed the developmental changes and localization of mBSP mRNA and protein in the mouse brain, using reverse transcription-polymerase chain reaction, Western blotting, and immunohistochemistry. Expression of mBSP was strong in the white matter and the nerve tracts after postnatal day 30, especially in the cerebellum and the medulla oblongata. These results suggest that mBSP contributes to development and sustaining the functions in the mouse brain.

Identification of Golli and myelin basic proteins in human brain during early development

The myelin basic protein gene (Mbp) encodes for the major myelin structural proteins and it is included in the Golli-Mbp gene complex. Previously, we observed MBP-like proteins in the human central nervous system (CNS) at developmental stages preceding myelination. In an effort to distinguish between Golli (HOG5 and HOG7) and MBP mRNAs and to determine their spatiotemporal distribution, we performed in situ hybridization using two human Golli specific probes: one corresponding to exon 5a absent from all MBP transcripts, and the other corresponding to exon 5c specific for HOG5. HOG7 transcript was observed first, in 5 gestational week-old embryos, whereas both Golli transcripts were detected at 6-7 weeks gestation in the proliferative zones of the entire CNS. Golli proteins immunoreactivity was observed in microglia and early neurons of the developing telencephalon. During midgestation (17-22 weeks gestation), at the onset of myelination, MBP and Golli mRNAs were observed in the telencephalic subventricular zone and occasionally in the future cerebral cortex. Developmental expression of the human Golli-Mbp indicates that the two Golli proteins have different onset of expression, distribution and possibly function. These results support the hypothesis that at least one of them, HOG7, may be involved in the regulation of early neurogenesis, while both may have additional, still undefined function at the onset of myelination.

The specificity of the myelin basic protein gene promoter studied in transgenic mice

The myelin basic proteins (MBPs) are a family of polypeptides that are predominantly expressed in the nervous system where they play a major role in myelination. We have generated four lines of transgenic mice carrying a transgene in which 1.34 kb of the 5'-flanking sequence of the mouse MBP gene was fused upstream of the coding region of the Escherichia coli lac Z gene in order to investigate developmental and tissue-specific expression of the MBP gene. Expression of both the lacZ transgene and the endogenous MBP gene followed a common developmental pattern in mouse brain. Transgene expression was detected in primary oligodendrocytes, but not in type 2 astrocytes. In addition, the lacZ gene product was expressed in epithelial cells of certain nonneural tissues, namely kidney, epididymis, ureter, and seminal vesicles. The ectopic expression of the transgene was associated with the development of DNase I hypersensitive sites at the site of insertion which was found to be within the intron 1 region of the endogenous MBP gene. The results reported here strongly suggest that the 1.34-kb 5'-flanking region of the MBP gene contains cis-regulatory elements that confer developmental regulation of the MBP gene, although this region appears to lack elements that restrict its expression to the nervous system.

Expression of Golli mRNA during development in primary immune lymphoid organs of the rat

The gene-of-the-oligodendrocyte lineage (Golli)-MBP transcription unit contains three Golli-specific exons together with eight exons of the "classical" myelin basic protein (MBP) gene, yielding alternatively spliced proteins which share amino acid sequence with MBP. Unlike MBP, a late antigen expressed only in the nervous system, Golli gene products are expressed pre- and post-natally at many sites. In this study, we determined the sequence of Golli in rat by RT-PCR and 5' RACE and showed that Golli sequences are expressed in primary lymphoid organs as early as e16.5, which could explain the anergic rat T cell response we previously observed in Golli-induced meningitis.

"Classic" myelin basic proteins are expressed in lymphoid tissue macrophages

"Classic" myelin basic proteins (MBPs) are demonstrated in lymph nodes of SJL mice by western blot and RT-PCR. Interestingly, expression of these "classic" MBPs was increased during the late relapsing phase of adoptive experimental autoimmune encephalomyelitis (EAE). When splenocytes from SJL mice were separated into macrophage versus B lymphocyte-enriched populations, intact MBP isoforms were demonstrated in the macrophage-enriched population while undetectable in the B lymphocyte-enriched population. RT-PCR demonstrated "classic" MBP transcripts in splenic macrophages, as well as in a macrophage cell line (RAW). The expression of "classic" MBPs in lymphoid tissue macrophages raises the possibility that MBP-specific T cells may be exposed to autoantigen outside the central nervous system (CNS).

Mice resistant to experimental autoimmune encephalomyelitis have increased thymic expression of myelin basic protein and increased MBP specific T cell tolerance

The relationship between expression of the autoantigens in thymi and susceptibility to autoimmune disease was determined in the experimental autoimmune encephalomyelitis (EAE) model. In two different sets of MHC congenic strains of mice characterized by differential susceptibility to EAE, levels of expression of MBP were shown to be higher in the more resistant strain. These data raised the possibility that more central tolerance to MBP may occur in more resistant strains. Differential tolerance was then evidenced by a decrease in T cell responses to MBP 83-102 in the more resistant strains. Together, these data indicate that the list of non-MHC genes involved in susceptibility to autoimmune disease should include genes which regulate expression of autoantigens in thymi.

Biology of oligodendrocyte and myelin in the mammalian central nervous system

Oligodendrocytes, the myelin-forming cells of the central nervous system (CNS), and astrocytes constitute macroglia. This review deals with the recent progress related to the origin and differentiation of the oligodendrocytes, their relationships to other neural cells, and functional neuroglial interactions under physiological conditions and in demyelinating diseases. One of the problems in studies of the CNS is to find components, i.e., markers, for the identification of the different cells, in intact tissues or cultures. In recent years, specific biochemical, immunological, and molecular markers have been identified. Many components specific to differentiating oligodendrocytes and to myelin are now available to aid their study. Transgenic mice and spontaneous mutants have led to a better understanding of the targets of specific dys- or demyelinating diseases. The best examples are the studies concerning the effects of the mutations affecting the most abundant protein in the central nervous myelin, the proteolipid protein, which lead to dysmyelinating diseases in animals and human (jimpy mutation and Pelizaeus-Merzbacher disease or spastic paraplegia, respectively). Oligodendrocytes, as astrocytes, are able to respond to changes in the cellular and extracellular environment, possibly in relation to a glial network. There is also a remarkable plasticity of the oligodendrocyte lineage, even in the adult with a certain potentiality for myelin repair after experimental demyelination or human diseases.

Age-dependent T cell tolerance and autoimmunity to myelin basic protein

Experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis, is induced by activating a subset of myelin basic protein (MBP)-specific T cells that have escaped tolerance induction. Here, we define the tolerance mechanisms that eliminate the majority of MBP-specific T cells from the periphery. We show that MBP-specific T cells undergo central tolerance mediated by bone marrow-derived antigen-presenting cells presenting exogenously derived MBP epitopes. The efficiency of tolerance is age dependent, reflecting the developmentally regulated expression of MBP. Dependence of tolerance on the amount of MBP expressed in vivo results in an age window of susceptibility to EAE in mice that peaks during puberty. These results suggest that factors regulating expression of self-antigens in vivo can influence susceptibility to autoimmunity.

An unexpected version of horror autotoxicus: anaphylactic shock to a self-peptide

EAE can refer either to experimental autoimmune encephalomyelitis or experimental allergic encephalomyelitis. Although EAE is classically a prototypic T helper 1 (TH1) cell-mediated autoimmune disease, it can also be induced by TH2 cells. Characteristically, the most severe manifestation of allergy, anaphylaxis, is associated with exposure to a foreign antigen that is often derived from medication, insect venom or food. We report here that, after self-tolerance to myelin is destroyed, anaphylaxis may be triggered by a self-antigen, in this case a myelin peptide. "Horror autotoxicus", which was initially described by Ehrlich, may not only include autoimmunity to self, it may also encompass immediate hypersensitivity to self, which leads to shock and rapid death.

The fine specificity of human T cell lines towards myelin basic protein peptides in southern Italian multiple sclerosis patients

We studied the relationship between the HLA specificities associated with multiple sclerosis (MS) susceptibility in southern Italy and the reactivity of the human myelin basic protein (hMBP) immunogenic peptides 84-98 and 143-168, using short-term T-cell lines established from 9 MS patients and from 8 healthy individuals. In our population, DR15 was significantly associated with MS (34.9% in MS versus 13.7% in healthy controls, P < 0.05). This result is in agreement with the association found in northern Europe, but not with data obtained in a population from the island of Sardinia (Italy). In MS patients the frequency of reactive T-cell lines (TCL), tested for fine specificity against the immunodominant hMBP peptides 84-98 and 143-168, was increased for the hMBP 143-168 peptide (P < 0.05) but not for the 84-98 peptide. Although this reactivity was higher in DR15+ MS patients than in DR 15- MS patients, it seemed not to be associated with DR15 specificity in the MS population. Furthermore, there were no significant differences in frequency of reactive TCL to hMBP peptide 84-98 in DR15-positive or DR15-negative MS patients. Consequently, it appears that peptide 84-98, considered as a relevant autoantigen, is not implicated in the pathogenesis of MS in our population from southern Italy.

Expression of myelin basic protein (MBP) epitopes in human non-neural cells revealed by two anti-MBP IgM monoclonal antibodies

Two monoclonal antibodies (1H6.2 and 45.30) were raised against MBP purified from human brain under experimental conditions that allowed MBP to retain binding to surrounding myelin lipids (human lipid-bound MBP (hLB-MBP)). 1H6.2 and 45.30 MoAbs were selected on the basis of their different binding properties to: hLB-MBP, human lipid-free-MBP (hLF-MBP) and bovine lipid-free-MBP (bLF-MBP). Although the isotype of both MoAbs was IgM, their specificity, as tested in ELISA assays against chemical haptens and unrelated protein antigens, was restricted to MBP. 1H6.2 and 45.30 MoAbs stained MBP from human brain white matter tissue extracts, as well as bLF-MBP, in Western blot assays. Both MoAbs stained oligodendrocytes and myelin in immunohistochemical analysis of white matter from human brain. Tissue sections from human peripheral nerves were labelled by 1H6.2 only, however, demonstrating that the MoAbs recognize two different epitopes. Epitopes recognized by 1H6.2 and 45.30 MoAbs were also expressed by a wide array of human non-neural cells of either normal or pathological origin, as evidenced by cytofluorimetric assays. In particular, MBP epitopes (MEs) were expressed by lymphoid cells as well as by cells which play a pivotal role in immune homeostasis and in the immune response, such as thymic epithelial cells and professional antigen-presenting cells. Both MoAbs were efficiently internalized by cells from a human B cell line, suggesting trafficking of MEs along the endocytic pathways. These findings support hypotheses regarding the role of MEs expressed by non-neural cells in establishing self-tolerance and/or in triggering the immune response against MBP antigen.

The fate of adoptively transferred quiescent encephalitogenic T cells in normal and antigen-tolerized mice

Adoptive transfer of quiescent encephalitogenic T cells to normal syngeneic recipients was without clinical effect. RT-PCR was used to assess localization of an adoptively transferred quiescent encephalitogenic T cell clone in normal and antigen-unresponsive mice prior to or after challenge with neuroantigen/CFA. The T cell clone was not detectable in lymphoid tissues prior to challenge with neuroantigen; however, following challenge, the clone was found in the spleen, lymph nodes and spinal cord of both normal and antigen-tolerized mice. The latter animals remained clinically normal. Non-activated encephalitogenic T cells transferred to wild-type recipients pretreated i.p. with neuroantigen/IFA were rendered unresponsive. Transfer of the same T cells to alpha/beta T cell-deficient mice pretreated with neuroantigen/IFA resulted in spontaneous disease indicating that an intact alpha/beta T cell system was required for development of the unresponsive state.

Cutting Edge: Myelin Basic Protein-Specific Cytotoxic T Cell Tolerance Is Maintained In Vivo by a Single Dominant Epitope in H-2k Mice

Multiple sclerosis (MS) is believed to be an autoimmune disease mediated by T cells specific for CNS Ags. MS lesions contain both CD4+ and CD8+ T lymphocytes. The contribution of CD4+ T cells to CNS autoimmune disease has been extensively studied in an animal model of MS, experimental autoimmune encephalomyelitis. However, little is known about the role of autoreactive CD8+ cytotoxic T cells in MS or experimental autoimmune encephalomyelitis. We demonstrate here that myelin basic protein (MBP) is processed in vivo by the MHC class I pathway leading to a MBP79–87/Kk complex. The recognition of this complex by MBP-specific cytotoxic T cells leads to a high degree of tolerance in vivo. This study is the first to show that the pool of self-reactive lymphocytes specific for MBP contain MHC class I-restricted T cells whose response is regulated in vivo by the induction of tolerance.

Golli-Induced Paralysis: A Study in Anergy and Disease

The Golli-MBP transcription unit contains three Golli-specific exons as well as the seven exons of the classical myelin basic protein (MBP) gene and encodes alternatively spliced proteins that share amino acid sequence with MBP. Unlike MBP, which is a late Ag expressed only in the nervous system, Golli exon-containing gene products are expressed both pre- and postnatally at many sites, including lymphoid tissue, as well as in the central nervous system. To investigate whether Golli-MBP peptides unique to Golli would result in neurological disease, we immunized rats and observed a novel neurological disease characterized by mild paralysis and the presence of groups of lymphocytes in the subarachnoid space but not in the parenchyma of the brain. Disease was induced by Th1-type T cells that displayed an unusual activation phenotype. Primary stimulation in vitro induced T cell proliferation with increased surface CD45RC that did not become down-regulated as it did in other Ag-stimulated cultures. Secondary stimulation of this CD45RChigh population with Ag, however, did not induce proliferation or IL-2 production, although an IFN-γ-producing population resulted. Proliferation could be induced by secondary stimulation with IL-2 or PMA-ionomycin, suggesting an anergic T cell population. Cells could adoptively transfer disease after secondary stimulation with IL-2, but not with Ag alone. These responses are suggestive of a chronically stimulated, anergic population that can be transiently activated to cause disease, fall back into an anergic state, and reactivated to cause disease again. Such a scenario may be important in chronic human disease.

Expression of autoimmune disease-related antigens by cells of the immune system

The process of thymic selection is critical for the generation of the mature T-cell repertoire, yet the nature of the self-peptides that serve this function is not known. Several studies suggest that tissue-specific auto-antigens are expressed in the thymus. We initiated this study to examine the expression of a panel of auto-antigens related to several autoimmune diseases in the thymus, peripheral lymphoid organs, and various cell lines. We looked for the expression of these antigens by reverse transcriptase-polymerase chain reaction, fluorescence-activated cell sorter (FACS) analysis, immunoblotting, and immunoprecipitation. We found that in the thymus there is evidence for the expression of a wide variety of disease-related self-antigens including myelin antigens, insulin, cardiac myosin, and retinal S antigen. By FACS analysis, several monoclonal anti-myelin basic protein antibodies were found to bind to immune cells. In Western blotting, we could find in the thymus and other lymphoid organs the expression of myelin basic protein, proteolipid protein, and cyclic nucleotide phosphodiesterase; in contrast, the staining for myelin oligodendrocyte glycoprotein, microtubule-associated Tau protein, and insulin were negative in these organs. The results of these studies confirm that there is evidence for the expression of a variety of auto-antigens in the immune system, both at the mRNA and protein levels, potentially enabling them to participate in the process of thymic education.

Myelin protein expression in lymphoid tissues: implications for peripheral tolerance

During chronic relapsing experimental autoimmune encephalomyelitis (EAE), T lymphocytes specific for myelin protein epitopes are stimulated in vivo. When epitopes are unique from the disease-initiating myelin protein epitope, this phenomenon has been termed "epitope spreading". These T-lymphocyte responses have been detected primarily in lymph node and spleen during the relapsing phase of disease. If myelin proteins are sequestered behind the blood brain barrier, a fundamental question arises: where does the in vivo stimulation of T lymphocytes occur during relapsing EAE? While it has been thought that epitope spreading may occur within the central nervous system (CNS), here we present data supporting a novel hypothesis. Epitope spreading during EAE may not occur within the CNS, but rather within lymphoid tissues. Both myelin basic protein (MBP) and proteolipid protein (PLP) are expressed at the RNA and protein level in lymph node, thymus and spleen of SJL mice with relapsing EAE. This myelin protein expression occurs within T lymphocytes, B lymphocytes and macrophages. Further, T-lymphocyte lines from SJL mice specific for the immunodominant and subdominant epitopes of MBP and PLP can recognize endogenous protein within cells derived from lymphoid tissues. Thus, immunologically relevant myelin proteins are endogenously produced and presented within lymphoid tissues. The hypothesis that epitope spreading occurs within lymphoid tissues would explain how myelin protein-specific T lymphocytes become activated outside the CNS to allow their passage through the blood brain barrier to form new CNS lesions during relapses.

Intrathymic expression of genes involved in organ specific autoimmune disease

Insulin, thyroglobulin and myelin basic protein (MBP) are implicated as autoantigens in the autoimmune diseases, insulin-dependent diabetes mellitus (IDDM), autoimmune thyroid-disease and multiple sclerosis. Self tolerance to these antigens, until recently only thought to be present extrathymically, is generally considered to be maintained by 'peripheral' mechanisms, such as clonal anergy or clonal ignorance. The techniques of reverse transcription and polymerase chain reaction (RT-PCR) were used to investigate the intrathymic expression of these genes. Expression was examined in mRNA isolated from complete adult rat thymus, various mouse thymic cell-types isolated from fetal thymic-organ cultures and from neonatal-mouse thymocyte subsets. mRNA for insulin, thyroglobulin and MBP were detected in unfractionated adult rat and embryonic mouse thymus. Rat thymus expressed both insulin I and II, while mouse thymus only expressed insulin II. Thyroglobulin and MBP, but not insulin mRNA were detected in mouse MHC class II+ thymic epthelial cells and class II+ dendritic cells and in certain thymocyte subsets. The presence of insulin, thyroglobubin and MBP mRNA in the thymus has important implications for the development of the T-cell repertoire, particularly for the mechanisms of tolerance that prevent autoreactivity to these antigens in healthy individuals.

Myelin basic protein in cerebrospinal fluid and other body fluids

Myelin basic protein (MBP) or a fragment thereof may enter cerebrospinal fluid (CSF) and other body fluids in an etiologically nonspecific fashion to provide information about the status of central nervous system (CNS) myelin damage. MBP immunochemically detected is referred to as MBP-like material (MBPLM). The clinical utility of the assay for MBPLM in CSF is to document the presence, continuation, or resolution of CNS myelin injury. The analysis of CSF for MBPLM is subject to many variables, among which are the antisera and the form of the assay utilized. The dominant epitope of CSF MBPLM is in the decapeptide of 80-89 from the intact MBP molecule of 170 residues. Normally, CSF has no detected MBPLM. Following an acute relapse of MS, MBPLM rises quickly in the range of ng/ml and rapidly declines and disappears. The presence of MBPLM in CSF in chronic and progressive phases of the disease is unusual, but it may sometimes be detected in low levels, depending on the assay used for detection. The level of CSF MBPLM is related to both the mass of CNS myelin damage and how recently it occurred. The level of CSF MBPLM rarely is elevated in optic neuritis. The level of CSF MBPLM is unrelated to CSF protein level, level of IgG, presence of oligoclonal bands or pleocytosis. CSF MBPLM has the potential of serving as a marker of therapeutic effectiveness in MS and does have predictive value for response to glucocorticoids given for worsening of disease. The detection of MBPLM in body fluids other than CSF would be of great value because of the resulting improved feasibility for objectively monitoring the natural history of MS and response to therapy. Studies on blood have yet to produce a valid assay of MBPLM. Urinary MBPLM, though different in its features from that in CSF, may provide a correlate, not with acute demyelination in MS as is the case for CSF, but with progression of disease.

Golli-MBP proteins mark the earliest stages of fiber extension and terminal arboration in the mouse peripheral nervous system

The Golli-myelin basic protein (MBP) transcription unit gives rise to two sets of products. One set (i.e., the MBPs) is expressed exclusively in myelin forming cells and the other set (i.e., the golli isoforms) is expressed in both oligodendrocytes and neurons in the CNS. The two major golli proteins, generated from RNAs transcribed from the most upstream promoter of the gene, contain MBP peptide sequences in their C-terminal halves and are, therefore, structurally and immunologically related to the MBPs. We have examined the distribution and localization of golli proteins in the mouse peripheral nervous system (PNS) using immunocytochemistry with a golli-specific antibody. Golli immunoreactivity was first observed in sensory and motor fibers of the mouse at E11 during fiber tract extension, but prior to the maturation of terminal connections. Once neuromuscular junctions had formed, golli immunoreactivity appeared in motor endplates and persisted to the latest age examined, P60. Golli immunoreactivity was also observed in the cell bodies and processes of the dorsal root ganglia throughout development. Strong staining in the PNS of the dysmyelinating mutant shiverer suggested that the major golli protein in peripheral fibers was the BG21 isoform. Interestingly, golli immunoreactivity was also found in adrenal chromaffin cells, which share a common neural crest derivation with other postganglionic neurons that express golli protein. These results suggest that in addition to its role in early forming neuronal systems of the CNS, golli protein also plays a role in the early development and maintenance of neurons in the PNS.

The shiverer mutation affects the persistence of Theiler's virus in the central nervous system

Theiler's virus persists in the white matter of the spinal cord of genetically susceptible mice and causes primary demyelination. The virus persists in macrophages/microglial cells, but also in oligodendrocytes, the myelin-forming cells. Susceptibility/resistance to this chronic infection has been mapped to several loci including one tentatively located in the telomeric region of chromosome 18, close to the myelin basic protein locus (Mbp locus). To determine if the MBP gene influences viral persistence, we inoculated C3H mice bearing the shiverer mutation, a 20-kb deletion in the gene. Whereas control C3H mice were of intermediate susceptibility, C3H mice heterozygous for the mutation were very susceptible, and those homozygous for the mutation were completely resistant. This resistance was not immune mediated. Furthermore, C3H/101H mice homozygous for a point mutation in the gene coding for the proteolipid protein of myelin, the rumpshaker mutation, were resistant. These results strongly support the view that oligodendrocytes are a necessary viral target for the establishment of a persistent infection by Theiler's virus.

Two proteins bind to a novel motif in the promoter of the myelin basic protein gene from mouse

The box 1 and 2 motif of the myelin basic protein (MBP) promoter is a potential regulatory sequence of the MBP transcription unit. A DNA fragment that contained the sequence of the box 1 and 2 motif from mouse was synthesized, and its protein binding properties were examined by gel-shift assays. The box 1 and 2 probe and nuclear extracts from mouse brain generated a pattern of six major DNA-protein complexes (a, b, c, d, e, and f). The box 1 and 2 probe and nuclear extracts from oligodendrocyte-like glioma cells 1C10 generated a pattern of DNA-protein complexes that exhibited only complexes a, b, e, and f. Complex b generated by extracts from 1C10 cells, however, was very intense compared to any of the other complexes. It was determined that dephosphorylation of the proteins in nuclear extracts from 1C10 cells with acid phosphatase significantly altered their DNA binding properties. Two proteins of minimum M, approximately 32 and approximately 38 kDa (MBP32 and MBP38) that bind to the box 1 and 2 motif were identified in these nuclear extracts by using a UV crosslinking method. MBP32 and MBP38 are found in cell types and tissues known to express the golli transcription unit of the golli-MBP gene complex and may be involved in the modulation of the MBP unit in those cells.

Epitope spreading occurs in active but not passive EAE induced by myelin basic protein

Using experimental allergic encephalomyelitis, EAE, as a model for the study of autoimmune demyelinating disease in the CNS, previous studies have indicated that spread may occur with respect to the specificity of T cell responses during disease. This phenomenon, known as epitope spreading, is central to therapeutic strategies in multiple sclerosis (MS). However, in EAE, the clinical course, neuropathology and immunopathogenesis vary depending upon host factors and the method of disease induction. Since passive EAE in SJL/J mice resembles MS clinically and neuropathologically, this model was chosen to study the immune phenomenon of epitope spreading. T cells specific for whole 18.5 kDa MBP were used to initiate disease since MBP or one of its naturally occurring cleavage fragments may initiate a more physiological immune response than one generated to an artificially designed synthetic peptide. While a progressive increase in T cell responsiveness specific for the immunodominant MBP 87-106 region was observed during disease, there was no evidence of either intermolecular epitope spreading to the immunodominant region of proteolipid protein (PLP) 139-151 or of intramolecular epitope spreading to the exon 2 encoded region of MBP, which is spliced out of 18.5 kDa MBP. In addition there was no shift in immunodominance toward the subdominant MBP 16-35 region during disease. In contrast during active EAE induced by MBP, epitope spreading to the immunodominant epitope of PLP, 139-151, was observed. These data demonstrate that immune responses generated during passive versus active EAE may differ, and suggest that significant epitope spreading does not occur in chronic relapsing demyelinating disease initiated with T cells specific for whole MBP in the absence of exogenous antigen, complete Freund's adjuvant and pertussis. Implications of these findings with regard to epitope spreading in MS are discussed.

Strain-related differences in the ability of T lymphocytes to recognize proteins encoded by the golli-myelin basic protein gene

Protein products of the golli-MBP gene complex, expressed in the nervous and lymphoid systems, contain sequences in common with sequences in 'classic' MBP, expressed exclusively in the nervous system. In this report, it was determined whether T cell lines (TCLs) specific for encephalitogenic epitopes of 'classic' MBP were able to recognize sequences within golli-MBP. TCLs derived from SJL mice specific for the immunodominant 83-102 sequence and the subdominant 19-27 sequence of 'classic' MBP recognized golli-MBP J37 and BG21, respectively. In contrast, TCLs derived from PL and B10.PL mice specific for the immunodominant 1-9 sequence of 'classic' MBP did not recognize this sequence within either J37 or BG21. These strain-related differences in the ability of golli-MBP proteins to stimulate 'classic' MBP-specific TCLs are discussed with respect to a possible influence on whether the course of EAE is relapsing (SJL) or monophasic (PL and B10.PL).

Membrane adhesion and other functions for the myelin basic proteins

The myelin basic proteins are a set of peripheral membrane polypeptides which play an essential role in myelination. Their most well-documented property is the unique ability to 'seal' the cytoplasmic aspects of the myelin membrane, but this is probably not the only function for these highly charged molecules. Despite extensive homology, the individual myelin basic proteins (MBPs) exhibit different expression patterns and biochemical properties, and so it is now believed that the various isoforms are not functionally equivalent in myelinating cells. We now think that while the major MBPs are intracellular adhesion molecules, some of the quantitatively less abundant isoforms that are expressed very early in development may have regulatory effects on the myelination program.

Differentially expressed genes after peripheral nerve injury

In an attempt to identify genes associated with Wallerian degeneration and peripheral nerve regeneration we have performed differential hybridization screening of a cDNA library from crushed rat sciatic nerve (7 days postlesion) using radioactively labeled cDNA prepared from poly(A)+ RNA of normal vs. crushed nerve. Screening of 5,000 randomly selected colonies yielded 24 distinct clones that were regulated following nerve injury. Fifteen of the differentially expressed sequences could be classified as induced, whereas 9 sequences appeared to be repressed at 1 week postcrush. Sequencing and computer-assisted sequence comparison revealed 3 classes of regulated cDNA clones representing 1) novel gene sequences (8 clones) including 3 transcripts containing a repetitive "brain identifier" (ID) element; 2) identified genes (7 clones) with previously undetected expression in the peripheral nervous system (PNS), such as apolipoprotein D, peripheral myelin protein 22kD (PMP22), SPARC (secreted protein, acidic and rich in cysteine), sulfated glycoprotein SGP-1, apoferritin, decorin, and X16/SRp20; and 3) identified genes (9 clones) with known expression in the PNS including, e.g., the myelin protein P0, gamma-actin, vimentin, alpha-tubulin, chargerin II, and cytochrome c-oxidase subunit I. Northern blot and polymerase chain reaction analyses with RNA from crushed and transected nerve demonstrated that sequences with related function, like the group of myelin genes, cytoskeleton genes, genes involved in RNA processing and translation, in lipid transport or energy metabolism showed closely related temporal patterns of expression during nerve degeneration and regeneration. Finally, we compared the differentially expressed genes identified at 7 days after crush injury (this investigation) with the regulated sequences isolated previously by De Leon et al. (J Neurosci Res 29:437-488, 1991) from a 3 day postcrush sciatic nerve cDNA library.

Thymic expression of the golli-myelin basic protein gene in the SJL/J mouse

The T cell antigen-specific repertoire is thought to be shaped by thymic expression of self molecules. Since a myelin basic protein (MBP)-like gene (golli-MBP) has been reported to be expressed by cells of the immune system, the present study was undertaken to determine whether the golli-MBP gene was expressed in the mouse thymus and, if so, to characterize transcripts of this gene in this organ. Using exon-specific primers for MBP and golli-MBP, cDNA from thymus and other tissues was amplified, and the amplified products analyzed by Southern blotting with exon-specific oligonucleotide probes. The amplified products were subcloned, and the inserts characterized by DNA sequencing. The thymic transcripts were found to contain golli-MBP exons 1, 2, 3, 5A, 5B, 5C, 6, 7, 8, and 11.

Encephalitogenic, myelin basic protein-specific T cells from naive rat thymus: preferential use of the T cell receptor gene V beta 8.2 and expression of the CD4-CD8- phenotype

Using a primary limiting dilution approach to generate T cell lines, we compared myelin basic protein (MBP)-specific T cell clones from naive unprimed Lewis rat thymuses with the corresponding T cell repertoire of primed rats. We found that in the native thymus repertoire MBP-specific, encephalitogenic T cell clones preferentially use T cell receptor V beta 8.2 genes, along with CDR3 sequences typical for the primed Lewis anti-MBP response. In contrast to T cells from primed immune organs, which all display the CD4+CD8- phenotype, the majority of naive thymus-derived T cell clones expressed reduced levels of the CD4 co-receptor. Some clones were completely CD4-CD8-, while others included CD4-CD8- subpopulations along with CD4+CD8- T cells. In the one mixed population examined in detail, the CD4-CD8- and CD4+CD8-T cell subpopulations used a T cell receptor with identical beta chain sequence. The data suggest that in the Lewis rat the biased T cell receptor gene usage by encephalitogenic T cells is a property of the natural thymic T cell repertoire, possibly as a consequence of positive selection. The unusually low expression of CD4 in the major histocompatibility complex class II-restricted autoreactive T cells could be related to their escape from negative selection within the thymus.

Myelin basic protein mediates extracellular signals that regulate microtubule stability in oligodendrocyte membrane sheets

Treatment of cultured oligodendrocytes with a monoclonal antibody to galactocerebroside (GalC) triggers a cascade of events including the redistribution of membrane surface GalC over internal domains of MBP and loss of microtubular structures within the sheets (Dyer and Benjamins: J Neurosci 8:4307-4318, 1988; Dyer and Benjamins: J Neurosci Res 24:212-221, 1989). In this report, wild type and myelin basic protein (MBP)-deficient shiverer oligodendrocytes were used to study the possible relationships between these events, and specifically to determine if MBP mediates signals which destabilize microtubular assemblies in cultured oligodendrocytes. We now show that MBP and GalC, which are both initially Triton X-100 soluble, become Triton X-100 insoluble following anti-GalC binding and anti-GalC:GalC complex redistribution, suggesting that the surface anti-GalC: GalC complexes become associated with cytoplasmic MBP. Mediation of the signaling event by MBP is further demonstrated by 1) a decreased phosphorylation of MBP in wild type oligodendrocytes after antibody binding, and 2) the absence of responses, such as GalC redistribution and microtubule loss, in MBP-deficient shiverer oligodendrocytes treated with anti-GalC. Continuous activation of the GalC/MBP pathway for 7 days in wild type oligodendrocytes results in enlarged cell bodies and production of numerous microprocesses, a morphology that is similar to MBP-deficient shiverer oligodendrocytes. A second signaling pathway which produces an opposite effect, i.e., the stabilization and apparent up-regulation of microtubular structures in cultured oligodendrocyte membrane sheets, remains functional in shiverer oligodendrocytes. Thus, MBP appears to be important for mediating extracellular signals that cause a loss of microtubular structures in oligodendrocyte membrane sheets and abnormal morphology.

Neurological mouse mutants and the genes of myelin

The prospect to create mouse mutants of virtually any cloned gene has renewed interest in the genetic analysis of mammalian brain development. A diverse group of spontaneous and engineered mouse mutants, characterized by a defect of myelin formation, has been intensively studied from the morphological to the molecular level. In this system, genetics has been successfully applied to analyze a corresponding set of membrane proteins which help to elaborate a defined structural entity, compact myelin. Shiverer, jimpy, Trembler, and protein zero (P0)-deficient mice demonstrate the overall function of myelination and have become models for human neurological diseases. They also illustrate some of the problems encountered in defining protein functions from complex mutant phenotypes.

The structural complexities of the myelin basic protein gene from mouse are also present in shark

The Golli-mbp gene complex contains two overlapping transcription units with two distinct promoters, of which the downstream (myelin basic protein [mbp]) promoter is more frequently used. A previous comparison of the downstream promoter sequences from shark and mouse allowed the identification of two DNA sequences called the boxes I and II and the wobble zone. The boxes I and II sequence is a composite cis-acting motif that is thought to be involved in the regulation of the downstream promoter. It contains sequences similar to T-antigen, MyoD/E2A, and glucocorticoid receptor-binding sites. The wobble zone codes for an exon (5a in the nomenclature of Campagnoni et al., 1993) that is included in messenger RNAs transcribed from the upstream promoter. The polypeptides encoded by this exon from shark and mouse are 86 and 84 amino acids long, respectively. These polypeptides are overall 59% identical and include a region (residues 41-75 in shark and 39-73 in mouse) that is 89% identical between the two species. A primary sequence analysis showed that each of these polypeptides contains an N-glycosylation site, phosphorylation sites for Ca2+/calmodulin-dependent protein kinase, protein kinase C and casein kinase II, and partial ATP- and GTP-binding sites. The shark polypeptide also contains a phosphorylation site for proline-directed protein kinase. These observations are consistent with the notion that the intricate structure and regulation of the Golli-mbp gene complex arose during vertebrate evolution within a common ancestor to sharks and mammals.