Epistemic_Statements  

CORD-19:16a812de72963ceda960a168236e8dbe91832d45 JSONTXT 11 Projects

Annnotations TAB TSV DIC JSON TextAE

Id Subject Object Predicate Lexical cue
T1 328-484 Epistemic_statement denotes Previous physiological studies demonstrated that demyelination in the CNS can result in conduction slowing and conduction block (McDonald and Sears, 1969) .
T2 624-713 Epistemic_statement denotes However, clinical and basic science observations have begun to challenge this hypothesis.
T3 1464-1563 Epistemic_statement denotes At least early in the disease, corticosteroid treatment accelerates recovery from clinical deficit.
T4 1564-1782 Epistemic_statement denotes Frequently, some dysfunction may persist after relapse, and an accumulation of such persistant clinical deficit ultimately results in a progressive impairment termed secondary progressive MS (Noseworthy et al., 2000) .
T5 1783-2040 Epistemic_statement denotes Although clinically characterized by pathological and functional hallmarks such as focally demyelinated lesions and gadolinium enhancement, as detected by magnetic resonance imaging (MRI), the cellular and molecular locus of MS is distinctly heterogeneous .
T6 2041-2224 Epistemic_statement denotes Although all lesions contain an inflammatory infiltration of T-cells and macrophages, further analysis suggests that four distinct patterns of pathology are present in active lesions.
T7 2533-2725 Epistemic_statement denotes This is consistent with previous reports show- 390 Remyelination as Neuroprotection ing abortive attempts at remyelination in MS lesions (Prineas and Connell, 1979; Prineas et al., 1989) (Fig.
T8 2731-2869 Epistemic_statement denotes The second pattern is unique in that actively degenerating myelin is associated with pronounced immunoglobulin and complement reactivity .
T9 3078-3225 Epistemic_statement denotes Finally, the third pattern is uniquely associated with greater loss of myelin-associated glycoprotein immunoreactivity than other myelin proteins .
T10 3226-3362 Epistemic_statement denotes This pattern is consistent with the concept of "dying-back oligodendrogliopathy," in which the primary injury is to the oligodendrocyte.
T11 3651-3815 Epistemic_statement denotes All lesions of any given patient are of the same phenotype, suggesting a single pathogenic mechanism within a patient but multiple mechanisms across the population.
T12 4449-4601 Epistemic_statement denotes The functional correlate of any of the patterns described previously is generally considered to be loss of axon conduction resulting from demyelination.
T13 4602-4775 Epistemic_statement denotes During the relapsing-remitting phase of MS, the regression of symptoms is likely due to resolution of inflammation and remyelination, resulting in a return of axon function.
T14 4776-4947 Epistemic_statement denotes However, as the disease progresses and as each round of repair accumulates demyelination that is not resolved, axonal function deteriorates (Noseworthy et al., 2000) (Fig.
T15 5140-5338 Epistemic_statement denotes Because axons are the absolute locus of neuronal function and transmission, it is likely that understanding and reversing axon failure and loss will be required for any rational therapeutic program.
T16 5339-5508 Epistemic_statement denotes Magnetic resonance imaging (MRI) studies in patients with MS have demonstrated only a weak correlation between lesion load and clinical deficits (Stevens et al., 1986) .
T17 5509-5737 Epistemic_statement denotes Moreover, pathological studies have demonstrated that some lesions observed by MRI are indeed demyelinated and frequently involve areas of CNS that should have resulted in neurological deficits, but do not (Bruck et al., 1997) .
T18 5738-5964 Epistemic_statement denotes Likewise, autopsy analysis has demonstrated that demyelination, sufficient to make the pathological diagnosis of MS, can be observed in individuals who during life remained normal in neurological function (Mews et al., 1998) .
T19 5965-6108 Epistemic_statement denotes These observations have suggested that demyelination may be required but not sufficient for the development of permanent neurological deficits.
T20 6109-6324 Epistemic_statement denotes Further challenge to the demyelination hypothesis is provided by studies that use magnetic resonance spectroscopy to sensitively and quantitatively measure axon-specific metabolites such as N-acetyl aspartate (NAA).
T21 6602-6885 Epistemic_statement denotes This finding suggests that a reduction in NAA may reflect both acute, but potentially reversible, axonal dysfunction associated with temporary demyelination, as well as chronic, irreversible loss of axons as a result of degeneration beyond the scope of any given demyelinated lesion.
T22 6886-7206 Epistemic_statement denotes The mechanisms by which demyelination induces axon dysfunction and axon degeneration remain unclear (Trapp et al., 1998) , but a number of recent studies suggest that multiple factors may be involved, ranging from increased accessibility of inflammatory mediators and immune effector cells, to a loss of trophic support.
T23 7676-7965 Epistemic_statement denotes Finally, changes in NAA associated with MS may reflect defects or dysregulation of axonal energy-storage mechanisms, as NAA-derived metabolic products such as acetyl coenzyme A may function to meet the high energy demands of axonal electrochemical conduction (Mehta and Namboodiri, 1995) .
T24 7966-7991 Epistemic_statement denotes This idea is particularly
T25 7992-8084 Epistemic_statement denotes Remyelination as Neuroprotection B A Figure 3 Evidence of "dying-back" oligodendrogliopathy.
T26 9307-9633 Epistemic_statement denotes However, in animals of susceptible MHC haplotypes (H-2 s,q,r,v,f,p ), the virus is cleared from neurons in the brain but persists in glial cells (Brahic et al., 1981; Rodriguez et al., 1983) and macrophages (Dal Canto and Lipton, 1982; Levy et al., 1992; Rossi et al., 1997) of the spinal cord white matter and brainstem (Fig.
T27 9639-9854 Epistemic_statement denotes This viral persistence is associated with chronic demyelination and stereotypical neurological impairment and paralysis due to the loss of axons (Drescher et al., 1997; Lipton 1975; Rodriguez and Miller, 1994) (Fig.
T28 10169-10356 Epistemic_statement denotes Resistance is a dominant trait that maps to H-2D, and genetic deletion or mutation of the D locus results in viral persistance and chronic demyelinating disease (Rodriguez et al., 1986) .
T29 10528-10898 Epistemic_statement denotes This resistance is associated with a robust antiviral cytotoxic Tcell response that develops in the gray matter of infected C57BL6 mice (Pena Rossi et al., 1991) , and immunological depletion of CD8 + T-cells or the genetic deletion of CD8 + T cells observed in β2-microglobulin knock-out mice results in viral persistence within otherwise resistant genetic backgrounds.
T30 11374-11670 Epistemic_statement denotes We have also previously demonstrated that cytotoxic T-cells appear to play a critical role in the injury of neurons and axons in both the acute (Howe and Rodriguez, unpublished observations) and chronic phases of Theiler's virus infection (Rivera-Quinones et al., 1998; Ure and Rodriguez, 2000; .
T31 12109-12291 Epistemic_statement denotes CNS proteinreactive T-cells are required for induction of EAE, and adoptive transfer of T-cells from immunized animals into naïve animals can elicit autoimmune-mediated inflammation.
T32 12495-12694 Epistemic_statement denotes While some evidence suggests that CD8 + and γδ-T cells may play a regulatory role in EAE (Segal, 2003) , CD4 + T-cells are considered to be the primary mediators of autoimmune-mediated demyelination.
T33 12801-13139 Epistemic_statement denotes Remyelination as Neuroprotection Axon damage is also associated with EAE (Ahmed et al., 2002; Kornek et al., 2000 Kornek et al., , 2001 Linker et al., 2002; Madrid and Wisniewski, 1977; Mancardi et al., 2001; Mead et al., 2002; Petzold et al., 2003; Pluchino et al., 2003; Raine and Cross, 1989; Raine et al., 1984; Storch et al., 2002) .
T34 13332-13595 Epistemic_statement denotes However, the mechanisms responsible for this axon damage are unclear, and, in contrast to the Theiler's virus model of MS, no study to date has identified a specific effector cell or process that is indispensable for axon injury but dispensable for demyelination.
T35 13906-14160 Epistemic_statement denotes Although a significant amount of evidence supports the role of the immune system in mediating and repairing the myelin damage induced by these two toxins, very little evidence is available regarding the extent of axon damage associated with these models.
T36 14187-14417 Epistemic_statement denotes (1997) showed that lysolecithin-induced demyelination sensitizes axons to conduction blockade induced by nitric oxide donors, suggesting that naked axons are more susceptible to soluble effector molecules released by immune cells.
T37 14684-14735 Epistemic_statement denotes Finally, a subtantial reduction in axon caliber was
T38 14736-14922 Epistemic_statement denotes Remyelination as Neuroprotection associated with chronic demyelination induced by cuprizone treatment, with axon diameter being reduced to 60% of normal after 16 weeks of demyelination .
T39 14923-15010 Epistemic_statement denotes Thus, every major animal model of demyelinating disease is associated with axon damage.
T40 15011-15317 Epistemic_statement denotes Because the methods used to induce demyelination in these models are extremely disparate, and because the cellular effectors of demyelination are variable across each of these models, it seems that axon failure, rather than mechanism of demyelination, is the critical feature of MS and animal models of MS.
T41 15551-15677 Epistemic_statement denotes Experiments carried out by our group suggest that at least one important cellular effector of axon damage is the CD8 + T-cell.
T42 16883-17047 Epistemic_statement denotes Our findings indicate that physiological function was likely preserved secondary to the upregulation and redistribution of sodium channels along demyelinated axons.
T43 18331-18491 Epistemic_statement denotes that MHC class I-restricted CD8 + T-cells are likely to be critical mediators of axon damage associated with demyelination in susceptible strains of mice ( Fig.
T44 18498-18646 Epistemic_statement denotes Further evidence in support of this CD8 + T-cell hypothesis is provided by our recent studies assessing axon transport in chronically infected mice.
T45 18845-19139 Epistemic_statement denotes However, we found that retrograde axonal transport was preserved in demyelinated mice with deletion of MHC class I (Ure and Rodriguez, 2002) , suggesting that the lack of CD8 + cytotoxic T-cells protected axonal integrity while not affecting demyelinated lesion load (Ure and Rodriguez, 2002) .
T46 19780-20039 Epistemic_statement denotes Finally, ongoing experiments in our laboratory indicate that VP2 peptide depletion of the MHC class I cytotoxic T-cell response to Theiler's virus infection preserves spinal axons, as measured by neurofilament staining, axon counting, and retrograde labeling.
T47 20242-20394 Epistemic_statement denotes The hypothesis that CD8 + T-cells are critical in the pathogenesis of Theiler's virus infection is relevant specifically to mice of the H-2 b haplotype.
T48 20728-20885 Epistemic_statement denotes The hypothesis probably does not explain the mechanism of demyelination and neurological deficit in susceptible strains such as SJL/J mice (H-2 s haplotype).
T49 20886-21337 Epistemic_statement denotes For example, disruption of MHC class I function by deletion of β 2 -microglobulin in SJL/J mice results in more demyelination and increased neurological deficit (Begolka et al., 2001) , and in the SJL/J strain it has been suggested that MHC class II-restricted T-cell response (Miller et al., 1987) , and epitope-spreading to myelin antigens may be the mechanism of demyelination and neurological deficit (Croxford et al., 2002; Miller et al., 1997) .
T50 21338-21595 Epistemic_statement denotes However, CD8 + MHC class I-restricted cytotoxic T-cells have definitely been implicated in human MS, and it is likely that demyelination and neurological dysfunction in humans are a combination of both CD8 + -and CD4 + -mediated mechanisms (Neumann, 2003) .
T51 21596-21782 Epistemic_statement denotes Recent pathological studies have shown that CD8 + T-cells may be the most common subset of T-cells in the MS brain and appear to be clonally expanded in MS lesions (Babbe et al., 2000) .
T52 21783-22121 Epistemic_statement denotes Recent experiments in collaboration with Hans Lassmann have demonstrated intense expression of MHC class I in oligodendrocytes, neurons, axons, and astrocytes in the MS lesion (Hoftberger et al., 2003) , and autopsy studies have demonstrated that CD8 + T-cells are statistically associated with axonal injury in MS (Bitsch et al., 2000) .
T53 22122-22428 Epistemic_statement denotes In addition, CD8 + T-cells have been shown to injure neurons and transect axons in vitro (Medana et al., 2000 (Medana et al., , 2001 , and imaging studies have indicated that axonal loss in MS is a direct correlate for disability (Narayanan et al., 1997; Truyen et al., 1996; van Waesberghe et al., 1999) .
T54 22429-22549 Epistemic_statement denotes These studies suggest that CD8 + T-cells may be the primary effectors for axonal injury and neurological deficits in MS.
T55 22550-22642 Epistemic_statement denotes Cytotoxic T-cell-induced cytotoxicity is mediated predominantly by two independent pathways.
T56 23075-23345 Epistemic_statement denotes At least one means of such physical contact is the generation of an "immune synapse," formed when the T-cell receptor complex of a cytotoxic T-cell encounters and binds to an MHC class I molecule presenting an appropriate peptide epitope on the surface of a target cell.
T57 23480-23630 Epistemic_statement denotes However, it has been shown in vivo that during pathological processes, the expression of MHC class I on the surface of neurons is rapidly upregulated.
T58 23952-24141 Epistemic_statement denotes In addition, soluble factors such as interferon-α/β (IFN-α/β), released as a result of infection, appear to be involved in the induction of MHC class I on CNS cells (Njenga et al., 1997b) .
T59 24302-24483 Epistemic_statement denotes This suggests that pathological processes such as demyelination that lead to conduction block may cause axons to become particularly vulnerable to cytotoxic T-cell-mediated killing.
T60 24898-24985 Epistemic_statement denotes Granzymes appear to be packaged within the cytolytic granule in complex with serglycin.
T61 25390-25658 Epistemic_statement denotes Some confusion currently exists regarding the role of perforin in the steps subsequent to cytolytic granule exocytosis, but the current model suggests that granzymes, either free or in complex with serglycin, bind to the surface of the target cell and are endocytosed.
T62 25659-25780 Epistemic_statement denotes This event appears to occur in the absence of perforin (Froelich et al., 1996; Pinkoski et al., 1998; Shi et al., 1997) .
T63 25781-26048 Epistemic_statement denotes Once endocytosed, however, perforin may function to facilitate the transfer of granzymes from target cell endosomes to the cytosol via endosomolysis, apparently without plasma membrane pore formation (Browne et al., 1999; Froelich et al., 1996; Metkar et al., 2002) .
T64 26269-26498 Epistemic_statement denotes Our laboratory has demonstrated, using Theiler's virus infection of C57BL/6 H-2 b mice, that perforin may be a critical component in the induction of neurological deficits once demyelination is established (Murray et al., 1998) .
T65 26629-26853 Epistemic_statement denotes Despite significant demyelination throughout the spinal cord, however, perforin-deficient C57BL/6 H-2 b mice failed to develop the significant functional deficits associated with demyelination in susceptible strains of mice.
T66 26854-27193 Epistemic_statement denotes Perforin-deficient mice did not acquire hind-limb paralysis, did not show a decrease in spontaneous activity, and did not develop signficant changes in hind-limb stride, suggesting that neurological deficits associated with demyelination are dependent on perforin, and, by extension, on functional cytotoxic T-cells (Murray et al., 1998) .
T67 27599-27988 Epistemic_statement denotes In these experiments, we found that wild-type B10.Q mice developed significant demyelination, a dramatic decrease in the frequency of large axons in the spinal cord, and significant neurological dysfunction, as measured by rotarod performance, but that large axon frequency and neurological function were relatively preserved in perforin-deficient B10.Q mice, despite marked demyelination.
T68 28582-28693 Epistemic_statement denotes Despite such widespread demyelination, however, these animals do not exhibit significant functional impairment.
T69 28694-28841 Epistemic_statement denotes This finding suggests that perforin-mediated killing by CD8 + T-cells is required for axon loss and functional deficits, but not for demyelination.
T70 28890-29004 Epistemic_statement denotes Thus, a death-inducing complex, called the death-inducing signaling complex (DISC), is formed at the Fas receptor.
T71 29365-29706 Epistemic_statement denotes Although cultured CD4 + and CD8 + T-cells can engage both the perforin and the Fas/FasL pathways, in vivo experiments suggest that MHC class I-dependent killing is dominated by the perforin pathway, whereas MHC class II-dependent elimination is almost entirely mediated by Fas/FasL interactions (Graubert et al., 1997; Schulz et al., 1995) .
T72 29707-29918 Epistemic_statement denotes Thus, a comparison between the relative role of perforin and Fas/FasL in demyelination and neurological deficit associated with Theiler's virus infection is a reasonable approach to address the CD8 + hypothesis.
T73 29919-30115 Epistemic_statement denotes Indeed, in support of the CD8 + hypothesis, and in contrast to the findings for perforin, the Fas/FasL system appears to play a minimal role in determining resistance to Theiler's virus infection.
T74 30519-30769 Epistemic_statement denotes In contrast, other investigators have suggested that in certain situations, MHC class I-restricted killing of neurons by virus-specific CD8 + T-lymphocytes is mediated through the Fas/FasL pathway, but not the perforin pathway (Medana et al., 2000) .
T75 30862-31112 Epistemic_statement denotes Although one report indicates that Fas is irrelevant to oligodendrocyte loss in MS lesions (Bonetti and Raine, 1997) , another provides evidence, at least in vitro, that Fas-mediated signaling contributes to a nonapoptotic injury of oligodendrocytes.
T76 31113-31411 Epistemic_statement denotes Of particular interest, FasL has been shown to protect neurons against perforin-mediated cytotoxicity (Medana et al., 2001) , raising the possibility that both these mechanisms of neuronal killing may interact with one another in as yet uncharacterized, and potentially extremely complicated, ways.
T77 32020-32252 Epistemic_statement denotes During viral infections, IFNγ is produced by natural killer (NK) cells, CD4 + , and CD8 + T-cells; however, the proportion of lymphocyte subsets responding to virus infection influences the contributions to IFNγ-mediated protection.
T78 32443-32692 Epistemic_statement denotes We demonstrated that IFNγ production by both CD4 + and CD8 + T-cell subsets is critical for resistance to Theiler's virus-induced demyelination and neurological disease, and that CD4 + T-cells make a greater contribution to IFNγ-mediated protection.
T79 34315-34540 Epistemic_statement denotes IFNγ deletion did not affect the humoral response directed against the virus; however, there was less expression of CD4, CD8, MHC class I, and MHC class II in the CNS of IFNγ −/− H-2 q mice as compared to IFNγ +/+ H-2 q mice.
T80 34771-34998 Epistemic_statement denotes These findings suggest that IFNγ plays a critical role in protecting spinal cord neurons from persistent infection and death, and that the cells responsible for production of this protective IFNγ appear to be cytotoxic T-cells.
T81 34999-35243 Epistemic_statement denotes Thus, a model in which CD8 + T-cells attack and kill axons and neurons via perforin must also include CD8 + and CD4 + T-cells that release potentially neuroprotective cytokines that accelerate viral clearance while sparing irreplacable neurons.
T82 36241-36402 Epistemic_statement denotes Therefore, we suggest that IL-6, normally considered to be an immune modulator during inflammation, signals to protect motor neurons from death, potentially in a
T83 36403-36595 Epistemic_statement denotes Remyelination as Neuroprotection manner analogous to ciliary neurotrophic factor (CNTF), a neurotrophic factor that also uses the gp130 signal transduction module Ransohoff et al., 2002) (Fig.
T84 36602-36949 Epistemic_statement denotes The relevance of IL-6-mediated neuroprotection to MS remains to be delineated, but the concentrations of IL-6 receptor components are altered in the cerebrospinal fluid and serum of patients with MS (Padberg et al., 1999) , suggesting that IL-6 signaling may be important to protect neurons during a demyelinating insult (Ransohoff et al., 2002) .
T85 37400-37611 Epistemic_statement denotes However, the exact mechanism(s) via which these factors function in MS, and the role each may play in protection of axons and neurons from damage or death associated with demyelination, remains to be discovered.
T86 38243-38503 Epistemic_statement denotes The role of each of these factors in limiting neurological dysfunction in MS is unknown, but is likely to be important, both for understanding the pathophysiology of the disease and for designing appropriate therapeutic interventions (Ransohoff et al., 2002) .
T87 38504-38679 Epistemic_statement denotes Moreover, the complexity of interactions possible between these factors and between elements of the immune system is certainly a critical consideration (Bonini et al., 2003) .
T88 38680-38784 Epistemic_statement denotes Obviously, the most efficacious therapy will be one that displays exquisite sensitivity and specificity.
T89 39216-39354 Epistemic_statement denotes Involvement of pathogenic autoantibodies in a particular dis-ease has been defined by several lines of experimental and clinical evidence.
T90 39355-39475 Epistemic_statement denotes For example, antibodies to a defined target should be present in the majority of patients that present with the disease.
T91 39620-39816 Epistemic_statement denotes Moreover, immunization with the target antigen, passive transfer of antibodies against the antigen, or transfer of antibodies from patients with the disease to naïve animals should induce disease.
T92 40037-40079 Epistemic_statement denotes Autoantibodies may also play a role in MS.
T93 40350-40522 Epistemic_statement denotes In addition, antibodies to MOG have been detected in association with disintegrating myelin in both human MS patients and in a marmoset model of EAE (Genain et al., 1999) .
T94 40710-40929 Epistemic_statement denotes Finally, we have shown that plasma exchange is effective in approximately 40% of cases with fulminant MS exacerbations, suggesting the presence of pathogenic autoantibodies in these patients (Weinshenker et al., 1999) .
T95 41087-41295 Epistemic_statement denotes A direct demonstration that autoreactive antibodies can enhance endogenous myelin repair came from our studies using Theiler's virus to induce chronic demyelinating disease in mice (Rodriguez et al., 1987a) .
T96 42252-42415 Epistemic_statement denotes Spontaneous remyelination is common in many mouse strains, but is limited in the SJL strain; often less than 10% of the total demyelinated lesion area is repaired.
T97 42416-42595 Epistemic_statement denotes The low background of spontaneous repair in these animals makes them an excellent model for the study of strategies to promote endogenous remyelination (Rodriguez et al., 1987b) .
T98 43345-43517 Epistemic_statement denotes This enhancement of remyelination was associated with proliferation or preservation of mature oligodendrocytes (Ludwin and Bakker, 1988; Prayoonwiwat and Rodriguez, 1993) .
T99 43848-44109 Epistemic_statement denotes Both of these monoclonal antibodies are polyreactive IgMs that bind to antigens on the surface of oligodendrocytes, suggesting that the activity of these monoclonal antibodies may involve direct stimulation of the myelin-producing cells (Asakura et al., 1996) .
T100 44110-44362 Epistemic_statement denotes Four additional oligodendrocyte-specific mouse IgMs (O4, O1, A2B5, and HNK1) were also shown to promote CNS remyelination (Asakura et al., 1998) , suggesting that this phenomenon was a general principle rather than an isolated immunological aberration.
T101 44363-44565 Epistemic_statement denotes Remyelination as Neuroprotection Using oligodendrocyte binding as a screening assay, we identified candidate human monoclonal antibodies that might also promote remyelination (Warrington et al., 2000) .
T102 45452-45781 Epistemic_statement denotes Generation of this recombinant monoclonal human IgM marked an important step forward in the production of a potential therapeutic agent aimed at ameliorating demyelination in patients with MS, as this antibody is available in essentially unlimited quantities and will not induce crossspecies reactivity if administered to humans.
T103 45887-45972 Epistemic_statement denotes Similar criteria can be applied to autoreactive antibodies involved in tissue repair.
T104 46075-46275 Epistemic_statement denotes All of the antibodies that promote remyelination bind to antigens on the surface of oligodendrocytes, suggesting that these antibodies function through direct stimulation of the myelinproducing cells.
T105 46521-46683 Epistemic_statement denotes Despite this antigenic promiscuity, however, remyelination-promoting antibodies bind only to a limited number of antigens on the surface of live oligodendrocytes.
T106 46880-46963 Epistemic_statement denotes Remyelination-promoting antibodies appear to be naturally occurring autoantibodies.
T107 47187-47395 Epistemic_statement denotes Such antibodies may represent a primordial form of the immune system that evolved to perform largely physiological functions rather than classical immune functions (Bouvet and Dighiero, 1998; Stewart, 1992) .
T108 47396-47555 Epistemic_statement denotes One of these nonimmunological functions may be to promote tissue repair, serving effectively as trophic factors for specific cell types (Bieber et al., 2001) .
T109 47556-47754 Epistemic_statement denotes The concept of an endogenous antibody-mediated repair system is consistent with our initial observation of enhanced remyelination after SCH or myelin antigen immunization (Rodriguez et al., 1987a) .
T110 47755-47898 Epistemic_statement denotes Immunization may mimic immune system exposure to CNS antigens that occurs after injury, resulting in an increased titer of anti-CNS antibodies.
T111 47899-48145 Epistemic_statement denotes Human IgMs from patients with macroglobulinemia were found to bind at high frequency to myelin antigens, suggesting that anti-CNS antibodies are common in the serum of individuals with no history of neurological damage (Warrington et al., 2000) .
T112 48146-48314 Epistemic_statement denotes Therefore, increasing the serum concentration of specific anti-CNS monoclonal antibodies may be a novel therapeutic treatment for human neurological injury and disease.
T113 48315-48518 Epistemic_statement denotes Because all of the remyelination-promoting monoclonal antibodies that we have identified so far bind to oligodendrocytes or myelin, it seems reasonable to suggest a direct effect on the recognized cells.
T114 48519-48661 Epistemic_statement denotes Other laboratories have demonstrated that oligodendrocyte-specific antibodies can induce biochemical and morphological changes in glial cells.
T115 48662-49033 Epistemic_statement denotes For example, Dyer and colleagues showed that antibodies directed against oligodendrocyte surface epitopes, including antibodies to galactocerebroside, sulfatide, and myelin/oligodendrocyte-specific protein, can induce changes in the organization of oligodendrocyte plasma membrane and can alter cytoskeletal structure (Dyer and Benjamins, 1988; Dyer and Matthieu, 1994) .
T116 49034-49339 Epistemic_statement denotes These changes in cellular structure were preceded by antibodyinduced calcium influx (Dyer, 1993; Dyer and Benjamins, 1990; , suggesting that the gating of calcium may play an important role in the regulation of oligodendrocyte structure and function, and may play a role in antibody-induced remyelination.
T117 49340-49579 Epistemic_statement denotes In support of this hypothesis, we recently reported similar changes in intracellular calcium concentration in oligodendrocytes after treatment with remyelinationpromoting monoclonal antibodies (Howe et al., 2004; Paz Soldan et al., 2003) .
T118 51478-51833 Epistemic_statement denotes Moreover, although the number of cells exhibiting an immediate response to treatment with the O4 monoclonal IgM was not affected by blocking several classes of plasma membrane Ca 2+ channels, pharmacologically blocking the activity of phospholipase C (PLC) significantly decreased the percentage of astrocytes that exhibited elevated intracellular Ca 2+ .
T119 52098-52446 Epistemic_statement denotes These data support the conclusion that the delayed response in oligodendrocytes is dependent on Ca 2+ entry through AMPA receptor Ca 2+ channels, whereas the immediate response in astrocytes is dependent on Ca 2+ release from endoplasmic reticulum stores, likely through PLC-mediated generation of IP 3 and gating of IP 3sensitive calcium channels.
T120 53061-53358 Epistemic_statement denotes The CDR3 is critical in the formation of the antigen-binding domain, and the difference in remyelination potential engendered by the sequence difference between 94.03 and CH12 suggests that antigen specificity, rather than some other component of antibody structure, is required for remyelination.
T121 53814-54011 Epistemic_statement denotes To establish a relationship between the ability of an antibody to elicit a Ca 2+ response and its ability to promote remyelination, we studied several remyelinationpromoting and control antibodies.
T122 54758-54993 Epistemic_statement denotes It is important to note that after treatment with antibody, calcium levels return to baseline, suggesting that the calcium influx is not toxic but is rather an element in a specific signal transduction cascade elicited by the antibody.
T123 55112-55352 Epistemic_statement denotes Thus, there appears to be a high degree of correlation between the ability of monoclonal IgM antibodies to promote remyelination and the stimulation of calcium influx, suggesting a potential signaling connection between these two phenomena.
T124 55353-55623 Epistemic_statement denotes Further evidence in support of a causal link between calcium signaling and remyelination is provided by experiments showing that rHIgM22 elicits a transient elevation in intracellular calcium in CG4 cells, a model of premyelinating oligodendrocytes (Howe et al., 2004) .
T125 56024-56154 Epistemic_statement denotes Biochemically, rHIgM22 appears to block cell death by preventing c-jun N-terminal kinase (JNK) signaling and caspase-3 activation.
T126 57089-57409 Epistemic_statement denotes Treatment with β-methylcyclodextrin, a cholesterol-chelating compound that effectively destroys lipid raft structure, prevented rHIgM22-induced survival signaling, suggesting that perhaps redistribution or aggregation of lipid raft domains is necessary for antibody-mediated signal transduction (Howe et al., 2004) (Fig.
T127 57416-57704 Epistemic_statement denotes This hypothesis is further supported by evidence that monovalent forms of sHIgM22 are unable to elicit remyelination or calcium signaling , suggesting that multivalency, and therefore oligomerization of cognate antigen, is necessary for the function of remyelination-promoting antibodies.
T128 57705-58033 Epistemic_statement denotes In fact, on the basis of the evidence at hand regarding antibodyinduced signaling, we hypothesize that remyelination-promoting antibodies function as soluble initiators of the type of clustering and consequent signaling described for integrins and proteoglycans involved in cell-cell adhesion and contactmediated signaling (Fig.
T129 58040-58216 Epistemic_statement denotes Integrins and cell surface proteoglycans are associated with plasma membrane lipid raft microdomains and with the oligomeric scaffolding protein caveolin (Baron et al., 2003) .
T130 59968-60200 Epistemic_statement denotes In parallel, lipid raft clustering of integrins and proteoglycans engages the MAPK JNK, leading to phosphorylation of the transcription factor c-jun, and association of c-jun with c-fos to form the AP-1 transcription factor complex.
T131 60201-60291 Epistemic_statement denotes This complex is a critical regulator of genes involved in cell proliferation (Lin, 2003) .
T132 61158-61386 Epistemic_statement denotes This partial activation brings the growth Stacking of the individual images shows the relative "patchiness" of the rHIgM22 staining pattern, suggesting that rHIgM22 antigen is localized to a specific plasma membrane microdomain.
T133 61510-61771 Epistemic_statement denotes Cholesterol chelation with methyl-β-cyclodextrin (β-MCD) completely abrogates the protective effect of rHIgM22, suggesting that signaling from lipid rafts is critical for the ability of rHIgM22 to rescue oligodendrocytes from oxidative stress-induced apoptosis.
T134 63580-63838 Epistemic_statement denotes This potentiation is accomplished by a clustering-dependent increase in the association of syndecan-4 with both PIP 2 and PKCα, resulting in the formation of a multimeric ternary complex of these three molecules (Bass and Humphries, 2002; Lim et al., 2003) .
T135 64456-64645 Epistemic_statement denotes As a result of this molecular linkage, NG2 is indirectly associated with the AMPA receptor within lipid rafts of oligodendrocyte progenitors (Hering et al., 2003; Stegmuller et al., 2003) .
T136 64646-64953 Epistemic_statement denotes Immature oligodendrocyte AMPA channels are involved in regulation of proliferation and differentiation (Yuan et al., 1998) , and the association of AMPA channels with NG2 suggests that adhesion-mediated clustering of NG2 may modify glial calcium signaling and thereby control maturation of oligodendrocytes.
T137 64954-65248 Epistemic_statement denotes It is interesting to note that AMPA channel function is substantially modified by lectin binding, and concanavalin A binding leads to desensitization of the AMPA channel and a consequent increase in calcium permeability in the absence of changes in glutamate binding (Thalhammer et al., 2002) .
T138 65448-65646 Epistemic_statement denotes Because NG2 does bear sialic acid residues, it is reasonable to speculate that the effect of deglycosylation or lectin binding is mediated by an alteration in NG2 association with the AMPA receptor.
T139 65812-66259 Epistemic_statement denotes The pentameric structure of the IgM antibodies we have identified as remyelination-promoting antibodies immediately suggests that clustering and multimerization of cell surface antigens is an important element in the signal transduction elicited downstream from antibody binding (Asakura et al., 1996 (Asakura et al., , 1998 Bieber et al., 2001; Miller et al., 1994; Rodriguez and Lennon 1990; Sommer and Schachner 1981; Warrington et al., 2000) .
T140 66260-66436 Epistemic_statement denotes Therefore, we propose that our remyelination-promoting antibodies function as soluble initiators of the type of clustering described previously for integrins and proteoglycans.
T141 66741-67113 Epistemic_statement denotes Moreover, several of these antibodies have been shown to alter oligodendrocyte morphology, initiate calcium signals, and induce differentiation (Dyer 1993; Dyer and Benjamins, 1989; , and the general lack of similar effects induced by IgG antibodies reactive with similar epitopes suggests that multimerization is an important element in the transduction of these effects.
T142 67114-67380 Epistemic_statement denotes It is also important to note, however, that cellular context is a critical factor in the signaling initiated by remyelination-promoting antibodies, as many of these antibodies recognize rather broad classes of molecules but only initiate signals in a limited manner.
T143 67381-67655 Epistemic_statement denotes Thus we hypothesize that remyelination-promoting antibodies recognize oligodendrocyte surface molecules that are presented within specific contexts, and that this recognition event leads to the clustering of signal transducers within plasma membrane lipid raft microdomains.
T144 67656-67744 Epistemic_statement denotes Myelin reactive autoantibodies may also enhance repair through more indirect mechanisms.
T145 67745-67926 Epistemic_statement denotes Antibodies binding to damaged oligodendrocytes and myelin may stimulate repair by enhancing the opsonization and clearance of myelin debris by macrophages (DeJong and Smith, 1997) .
T146 67927-68094 Epistemic_statement denotes Large numbers of macrophages are often observed in demyelinated lesions, and phagocytosis of myelin debris may be an important prerequisite to efficient remyelination.
T147 68095-68330 Epistemic_statement denotes However, our most recent data indicate definitively that the Fc portion of the antibodies is not required for remyelination induced by sHIgM22 , and this critical piece of information has focused our attention on the direct hypothesis.
T148 68577-68769 Epistemic_statement denotes An identical preimmunization strategy was used, and therefore the antibody response is likely to be the same as in our earlier studies using the Theiler's virusmediated model of demyelination.
T149 69156-69339 Epistemic_statement denotes It was hypothesized that anti-SCH antibodies promoted axon regeneration by blocking in vivo myelin-associated inhibitors of axon outgrowth (Ellezam et al., 2003; Huang et al., 1999) .
T150 69340-69512 Epistemic_statement denotes However, the SCH antisera did not contain elevated titers of antibodies to known myelin inhibitors (Nogo, myelin associated glycoprotein, chondroitin sulfate proteoglycan).
T151 69513-69698 Epistemic_statement denotes Therefore, myelin reactive antibodies might be useful not only to promote myelin repair after demyelinating disease but also for the treatment of axonal damage after spinal cord injury.
T152 69699-69808 Epistemic_statement denotes Such antibodies may be administered exogenously or generated in vivo via appropriate immunization strategies.
T153 70225-70450 Epistemic_statement denotes An understanding of these mechanisms should open up significant new areas for the development of antibody-based therapeutics and perhaps small molecule-based therapeutics and vaccines for induction of the reparative response.
T154 70451-70591 Epistemic_statement denotes Remyelination is an important therapeutic goal for the treatment of neurological disease and is likely to protect axons from further injury.
T155 70761-70887 Epistemic_statement denotes The loss of oligodendrocytes and myelin normally associated with demyelinating diseases such as MS is, of course, devastating.
T156 70888-71134 Epistemic_statement denotes However, rational therapeutic approaches that may be within reach, including treatment with remyelinationpromoting antibodies or transplantation of oligodendrocyte progenitors, will likely repair and reverse myelin-related damage and dysfunction.
T157 71135-71323 Epistemic_statement denotes In contrast, the loss of neurons, axons, and synaptic connections that may result after repeated bouts of demyelination is likely to be a far more complex and intractable problem to solve.
T158 71324-71543 Epistemic_statement denotes Axons and synapses are the final physical manifestation of the neural connectivity and plasticity that develops over the lifetime of an individual; replacing these structures once lost may simply prove to be impossible.
T159 71544-71923 Epistemic_statement denotes Therefore, it is critical that strategies be developed for protecting and maintaining axons during demyelinating episodes associated with MS. Obviously, the ultimate goal is to prevent MS altogether, but in the short term, a reasonable goal is to rapidly promote remyelination and thereby protect neurons and axons from damage and death inflicted by exposure to immune mediators.
T160 71924-72139 Epistemic_statement denotes We propose that treatment with remyelination-promoting growth factor-like human IgM natural autoantibodies may be an efficacious method for quickly repairing demyelinated lesions and maintaining axonal connectivity.
T161 72140-72275 Epistemic_statement denotes Likewise, another important goal of our group is to better understand the immune effector cells involved in damaging axons and neurons.
T162 72276-72507 Epistemic_statement denotes There is substantial evidence that CD8 + T-cells are a key mediator of axon killing in patients with MS, and we will continue to study the role of these cells in a number of animal models of MS, including the Theiler's virus model.
T163 72624-72689 Epistemic_statement denotes The data to support this hypothesis can be summarized as follows.
T164 72690-72842 Epistemic_statement denotes First, susceptibility vs. resistance to viral persistance and demyelination maps to the D region molecule of the class I gene (Rodriguez et al., 1986) .
T165 73254-73417 Epistemic_statement denotes Fourth, cytotoxic T-cell-mediated killing can be demonstrated for T-cells isolated directly from the infected CNS without in vitro stimulation (Lin et al., 1995) .
T166 74218-74407 Epistemic_statement denotes Preservation of physiological function was likely due to preservation of axons, and, in fact, we showed that axons upregulated and redistributed sodium channels along demyelinated segments.
T167 74594-74716 Epistemic_statement denotes However, axonal transport was preserved in demyelinated mice with deletion of β2-microglobulin (Ure and Rodriguez, 2002) .
T168 74897-75260 Epistemic_statement denotes These results suggest that axonal injury mediates neurological impairment during the chronic phase of Theiler's virus infection that is separable from virus-induced demyelination, and also suggest that CD8 + cytotoxic T-lymphocytes directed against a specific viral peptide presented by MHC class I on axons and neurons may play an important role in this process.
T169 75261-75431 Epistemic_statement denotes We favor the hypothesis that demyelination is necessary but not sufficient for development of permanent deficits in primary demyelinating disorders of humans and animals.
T170 75578-75746 Epistemic_statement denotes This secondary injury to the axon may be the result of either (1) T-cell cytotoxicity or (2) failure of neurotrophic support from death of myelinating oligodendrocytes.
T171 75747-76073 Epistemic_statement denotes It is not known how long an axon can remain demyelinated in the CNS before death or remyelination takes place; however, strategies to prevent cytotoxic T-cell-mediated injury to axons and strategies to maintain axons may ultimately prove to be the most efficacious means of preventing long-term disability after demyelination.
T172 76074-76319 Epistemic_statement denotes Rapid remyelination of these preserved axons, induced perhaps by treatment with growth factor-like human monoclonal IgM antibodies directed against myelin antigens, may protect them from further injury and thereby preserve neurological function.