Multiple sclerosis: serum-induced demyelination in vitro. A light and electron microscope study

Statistical physics approach to quantifying differences in myelinated nerve fibers

We present a new method to quantify differences in myelinated nerve fibers. These differences range from morphologic characteristics of individual fibers to differences in macroscopic properties of collections of fibers. Our method uses statistical physics tools to improve on traditional measures, such as fiber size and packing density. As a case study, we analyze cross–sectional electron micrographs from the fornix of young and old rhesus monkeys using a semi-automatic detection algorithm to identify and characterize myelinated axons. We then apply a feature selection approach to identify the features that best distinguish between the young and old age groups, achieving a maximum accuracy of 94% when assigning samples to their age groups. This analysis shows that the best discrimination is obtained using the combination of two features: the fraction of occupied axon area and the effective local density. The latter is a modified calculation of axon density, which reflects how closely axons are packed. Our feature analysis approach can be applied to characterize differences that result from biological processes such as aging, damage from trauma or disease or developmental differences, as well as differences between anatomical regions such as the fornix and the cingulum bundle or corpus callosum.

Neuromyelitis optica: a demyelinating disease characterized by acute destruction and regeneration of perivascular astrocytes

BACKGROUND

A serum antibody directed against astrocytes is present in a high proportion of patients with neuromyelitis optica (NMO). The pathogenicity of the antibody is uncertain because no consistent astrocyte lesion is known to occur in NMO.

OBJECTIVE

To determine whether there is an astrocyte lesion in NMO and if this differs from astrocyte changes in multiple sclerosis (MS).

METHODS

Astrocyte pathology in early (still-myelinated) lesions and subacute NMO and MS lesions was examined immunohistochemically and in sections stained for astrocytes using routine histological techniques.

RESULTS

Demyelination in early NMO lesions is accompanied by oligodendrocyte apoptosis in a pattern identical to that seen in MS and this is preceded by an abrupt destruction of perivascular astrocytes. Reparative astrogliosis is effected by a population of unipolar, new astrocytes. Evidence of a different type of astrocyte lesion was found in MS.

DISCUSSION

The findings add to experimental evidence that the antibody is pathogenic. They also raise the possibility that demyelination in MS may be a bystander effect of an astrocyte lesion, i.e. that MS is not a disease primarily of myelin and oligodendrocytes.

Immune responses against the myelin/oligodendrocyte glycoprotein in experimental autoimmune demyelination

Myelin/oligodendrocyte glycoprotein (MOG) is a surface-exposed antigen of myelin and an important target for autoimmune responses which mediate inflammatory demyelination in the central nervous system. Experimentally, MOG induces strong pathogenic T cell responses in many strains of laboratory animals. Immunological studies in humans also identify MOG as a surprisingly prevalent antigenic molecule among the myelin proteins. In addition, the encephalitogenic properties of MOG are linked to the induction of antibody responses which have been demonstrated to directly promote central nervous system demyelination, a hallmark neuropathological feature in disorders such as human multiple sclerosis. Factors responsible for autoimmunity to MOG likely include genetic influences as well as other mechanisms, which are the subject of intense investigation. This article reviews experimental data currently available on specificity and pathogenic roles of T cell and antibody responses against MOG, which have implications relevant to multiple sclerosis and related disorders.

The role of anti-myelin (auto)-antibodies in the phagocytosis of myelin by macrophages

Plasma cells secreting antibodies directed to myelin components are present in CNS of MS patients and although the pathogenic role of such antibodies has yet to be established it is apparent from animal studies that anti-myelin antibodies are involved in myelin damage. In this study, we have investigated the effect of disease-promoting anti-myelin mAb on the phagocytosis of myelin by macrophages. Monoclonal antibodies directed to myelin basic protein (MBP)--clones 1, 12, 17, 22, 26, proteolipid protein (PLP), galactocerebroside (GalC) and myelin oligodendrocyte glycoprotein (MOG)--clones Y1, Y4, Y6, Y7, Y9, Y10, Y11 and Z12 were incubated with purified murine myelin labeled with DiI. The degree of phagocytosis of antibody-treated myelin by murine macrophages in vitro was determined using a quantitative flow cytometric assay. In comparison to untreated myelin pretreatment with myelin-specific mAb modified the degree of phagocytosis. The degree of opsonization of myelin was dependent on the isotype of antibody and the epitope recognized in addition to the ability of the mAb to fix complement. The greatest degree of opsonization of myelin was observed with the monoclonal antibody MOG Z12 that has previously been shown to enhance EAE and augment demyelination. These findings suggest a major role for anti-myelin antibodies, in particular antibodies directed to MOG, for the phagocytosis of myelin by macrophages in vitro. This may have relevance to the pathogenesis of myelin damage in vivo and provide a helpful tool for the classification of heterogeneous diseases such as MS.

Demyelination in primate autoimmune encephalomyelitis and acute multiple sclerosis lesions: a case for antigen-specific antibody mediation

Neuropathological and ultrastructural features of central nervous system demyelination were compared in marmoset experimental autoimmune encephalomyelitis (EAE) induced with myelin/oligodendrocyte glycoprotein (MOG), and in 3 cases of multiple sclerosis (MS) displaying recent lesions. At the edges of EAE and MS lesions, a zone of myelin vacuolation was common, whereas in the lesion proper, myelin sheaths were consistently transformed into vesiculated membranous networks. These networks became dissociated from axons by cell processes from macrophages. Oligodendrocytes were remarkably spared and evidence of myelin repair was present but not prominent. Axonal pathology was more common in the MS material than in marmoset EAE. Immunocytochemistry, using gold-labeled encephalitogenic peptides of MOG and silver enhancement to detect MOG autoantibodies, revealed the presence of MOG-specific autoantibodies over vesiculated myelin networks. Gold-labeled antibody to IgG also gave a positive reaction. Gold-labeled peptide of myelin basic protein did not react with MOG/EAE tissue, but the same conjugate gave positive staining in MS (and in marmoset EAE induced by whole white matter), perhaps indicating broader spectrum immunoreactivity or sensitization to myelin antigens. Thus, vesicular disruption of myelin was a constant feature in these evolving, highly active lesions in primate EAE and MS and appeared causally related to the deposition of antigen-specific autoantibodies.

Identification of autoantibodies associated with myelin damage in multiple sclerosis

The molecular mechanisms underlying myelin sheath destruction in multiple sclerosis lesions remain unresolved. With immunogold-labeled peptides of myelin antigens and high-resolution microscopy, techniques that can detect antigen-specific antibodies in situ, we have identified autoantibodies specific for the central nervous system myelin antigen myelin/oligodendrocyte glycoprotein. These autoantibodies were specifically bound to disintegrating myelin around axons in lesions of acute multiple sclerosis and the marmoset model of allergic encephalomyelitis. These findings represent direct evidence that autoantibodies against a specific myelin protein mediate target membrane damage in central nervous system demyelinating disease.

The Norton Lecture: a review of the oligodendrocyte in the multiple sclerosis lesion

The mechanisms involved in the elimination of oligodendrocytes and myelin from the demyelinated plaque of multiple sclerosis (MS) are inextricably intertwined and yet most investigations tend to consider them separately. This short review revisits the problem of oligodendrocyte pathology in MS and attempts to put the topic into perspective by examining the numerous immunologically-active molecules associated with the oligodendrocyte, some, but not all, cross-reactive with myelin. The consensus of opinion is that myelin is the primary target in MS but that oligodendrocytes are eventually lost from the lesion. Reappraisal of recent and past works brings into focus a possible key role for soluble mediators, in particular antibody and the pro-inflammatory cytokine, TNF alpha, in oligodendrocyte loss and myelin in MS. Despite extensive neuropathologic investigation by a number of laboratories, no evidence has yet been found to support the concept that apoptosis might account for oligodendrocyte depletion in MS, even though molecules belonging to the apoptotic cascade can be expressed by oligodendrocytes in and around lesions. Indeed, abundant evidence has been presented to show that oligodendrocytes initially respond to the demyelinating insult in MS by proliferating and elaborating new myelin but, no doubt due to the relentless progression of inflammatory events, the cells are eventually lost, probably via a cytolytic pathway. Strategies to block the progression of CNS inflammation in EAE and MS appear to promote the survival of oligodendrocytes and to enhance remyelination. Such strategies appear to hold much promise for the MS patient.

Time course of biochemical and immunohistological alterations during experimental allergic encephalomyelitis

A comprehensive biochemical, immunological and histological study was undertaken during different stages of experimental allergic encephalomyelitis (EAE). Wistar rats with EAE induced by sensitization with bovine myelin showed a maximum decrease of body weight 14-16 days post-inoculation (dpi), coincident with the appearance of the paralysis symptom (acute period). Quantitation of some brain components indicated a temporal dissociation among the alterations observed. The higher diminution of myelin basic protein (MBP) occurred at 6 dpi and then increased to reach 21 dpi, a normal value. Also, the activity of 2',3'-cyclic nucleotide 3'-phosphohydrolase was reduced by 40% with respect to control animals only at 6 dpi. The total lipid content was normal; however, among the individual lipids, sulfatides were principally degraded during the acute stage but the amount of cerebrosides was decreased during the recovery period (29-40 dpi). Free cholesterol was similar in both groups of animals, whereas cholesterol esters were detected in EAE animals from 14 to 40 dpi. Central nervous system meningeal and parenchymal infiltration with mononuclear cells was recognized principally at 14 dpi, but some of cells were still present at 40 dpi. Deposits of immunoglobulins in the infiltrated regions as well as in spinal cord motor neurons were observed among 14-29 dpi. Total circulating antibodies to MBP began to increase at 14 dpi, reaching a plateau at 21 dpi and then maintaining this value until 40 dpi. However, the population of anti-MBP antibodies that also recognizes the neuronal protein synapsin was only present at 14 dpi. The present results suggest that the neurological symptoms can be related to some early changes in the myelin membrane followed by alterations involving neuronal structures. The existence of immunological factors against some epitopes in MBP that also recognize a synaptosomal protein might account, at least in part, for the axonal damage and disruption of the normal interneuronal activity in EAE and lead together with the alterations in some specific myelin constituents and the concomitant CNS inflammatory process to the observed hindlimb paralysis.

Paranodal structural abnormalities in rat CNS myelin developing in vivo in the presence of implanted O1 hybridoma cells

O1 hybridoma cells, which produce a monoclonal IgM antigalactocerebroside, were implanted into the spinal cords of immature and mature rats and the cords examined 5-24 days later. Study of the younger group, in which myelin was developing at the time of implantation, revealed examples of abnormal myelin sheaths in which the repeat period was markedly increased. The paranodal regions of these abnormal sheaths were superficially normal in configuration; i.e. myelin lamellae terminated one by one as 'terminal loops' that indented the axolemma and formed normal axoglial junctions displaying periodic 'transverse bands'. Neighbouring terminal loops are normally joined by tight junctions that block passage of tracers from the paranodal periaxonal space into the compact myelin, as seen after implantation of a control hybridoma. In the abnormal sheaths that developed after O1 implantation, in contrast, terminal loops were usually widely separated from each other. As a result, multiple pathways from the paranodal periaxonal space into the myelin sheath remained patent, forming potential routes for shunting nodal action currents. This subtle abnormality could thus compromise conduction, even though the sheaths might appear to be normally myelinated at the histological level. Equivalent abnormalities in human neurological diseases, including multiple sclerosis and paraproteinemic neuropathies, could underlie functional loss in the absence of frank demyelination.

Inhibition of CNS myelin development in vivo by implantation of anti-GalC hybridoma cells

Implantation of hybridoma cells that secrete a monoclonal antigalactocerebroside into the dorsal columns of < or = 9-day-old rat spinal cord results in failure of development of dorsal column myelin in the vicinity of the implant. Clusters of apparently undamaged amyelinated axons remain among the hybridoma cells. Ventral myelin is unaffected. These in vivo results support antibody-mediated inhibition of myelin formation as a potential mechanism underlying failure of remyelination in multiple sclerosis.

Phagocytosis of myelin by astrocytes in explants of adult rabbit cerebral white matter maintained on Gelfoam matrix

The role of astrocytes in the process of demyelination has been controversial. A culture system in which explants of adult cerebral rabbit white matter were maintained on a Gelfoam matrix was used for evaluating the phagocytosis of myelin by astrocytes without an influx of phagocytic cells derived from actively circulating blood-borne cells. Adult neurons were not viable for more than a few days in these explant cultures, thus resulting in empty myelin sheaths following loss of their axons. After 7 days in vitro, astrocytes, recognized by positivity for glial fibrillary acidic protein by electron microscopic immunocytochemistry, contained numerous membrane-bound vesicles filled with myelin in various stages of degradation. Although the majority of macrophage-like cells were negative for glial fibrillary acidic protein, a minority were positive, in spite of the lack of bundles of intermediate filaments, and were interpreted as astrocytic. Astrocytes were also often positive for glutamine synthetase. This study presents evidence suggesting that astrocytes may actively participate in the phagocytosis and degradation of myelin, a function generally attributed to reactive macrophages.

EAE cerebrospinal fluid augments in vitro phagocytosis and metabolism of CNS myelin by macrophages

Previous studies from this laboratory have shown that CNS myelin is phagocytized and metabolized by cultured rat macrophages to a much larger extent when myelin is pretreated with serum containing antibodies to myelin constituents than when it is left untreated or pretreated with non-specific serum. In this study the effect of cerebrospinal fluid (CSF) from rabbits with experimental allergic encephalomyelitis (EAE) in promoting myelin phagocytosis was examined. Fourteen rabbits were immunized with purified myelin in Freund's complete adjuvant, seven of which developed clinical EAE symptoms. Serum and CSF were collected from EAE and control rabbits, and the CSF was centrifuged to remove cells. Sera and CSF from these rabbits and from Freund's adjuvant-immunized controls and untreated controls were measured for IgG content by radial diffusion assay, their myelin antibody characteristics were analyzed by immunoblots, and the ability of these serum and CSF samples to promote myelin phagocytosis when used for myelin opsonization was examined. The ability of a CSF sample to enhance radioactive myelin uptake and phagocytosis by cultured macrophages as measured by the appearance of radioactive cholesterol ester was linearly proportional to its total IgG titer, and correlated approximately both with clinical symptoms of the animal and the presence of antibody against the myelin constituents myelin basic protein, proteolipid protein, and galactocerebroside. The cholesterol esterification activities of EAE sera correlated to a lesser extent with IgG levels and clinical symptoms.(ABSTRACT TRUNCATED AT 250 WORDS)

[Myelination, demyelination and re-myelination in the central nervous system]

The myelin sheaths that surround axons in the CNS are made and maintained by oligodendrocytes. These glial cells can form variable numbers of myelin segments (internodules): from 1 to 200 so that when one oligodendrocyte is destroyed with preservation of the axon, many internodules can be lost, constituting a demyelinating process. As a consequence of the destruction of myelin and sheath cells a rapid and abundant cell response takes place. The response is made up by resident (microglia) and haematogenous phagocytes which phagocytose myelin and cellular debris leaving the axons demyelinated. Demyelinated axons may either stay demyelinated and clumped together or they may be separated by astrocytic processes, yet they can be remyelinated. The occurrence of remyelination depends upon the intensity and time of exposition to the demyelinating agent. Remyelination in the CNS with complete restoration of conduction may be made by oligodendrocytes or Schwann cells which invade the CNS when astrocytes are destroyed.

Multiple sclerosis: effects of activated T-lymphocyte-derived products on organ cultures of nervous tissue

Supernatants from multiple sclerosis (MS) T-lymphocytes cause damage to both myelin and glial cells in cerebellar cultures assessed visually and by radiolabel release. Control T-lymphocytes, even after phytohaemagglutinin (PHA) stimulation, yielded supernatants which induced only slight damage, and at later times patients with other neurological diseases (OND) gave variable results. These differences suggest that MS T-lymphocytes are pre-activated in vivo to produce demyelinating factors while control T-lymphocytes are not pre-activated to the same extent. The visual evidence of activation of cerebellar macrophage-like cells was a common finding after MS T-lymphocyte supernatant treatment but there was no correlation with the severity of demyelination. There was a positive correlation between the percentage IL-2 receptor-bearing lymphocytes and the degree of supernatant-induced in vitro demyelination.

Inhibition of glial proliferation in vitro by serum from patients with multiple sclerosis

Primary cell cultures from fetal rat CNS have been employed to evaluate the effects caused by the addition of serum from patients affected by multiple sclerosis (MS). MS-serum supplemented media caused a decrease in [3H]-thymidine incorporation into the cultures, thus indicating an inhibitory effect on proliferating glial cells. Sera from patients in remission stage of the disease showed an inhibitory effect not significatively lower than those from patients in acute stage. These results suggest that glial cells may be a target of circulating factors present in MS.

Release of leukotriene B4 from sublethally injured oligodendrocytes by terminal complement complexes

In the present study, the interaction of the terminal complement complexes with oligodendrocytes was investigated for observation of its effect on membrane lipid hydrolysis. [14C]Arachidonic acid was incorporated into the membrane lipids of cultured oligodendrocytes before sensitization with anti-galactocerebroside antiserum. Cells were then exposed to excess C6-deficient rabbit serum reconstituted with limiting doses of C6 to form various numbers of C5b-9 complexes. Qualitative analysis of the supernatants by HPLC revealed the presence of compounds that coeluted with arachidonic acid and its oxygenated derivatives, prostaglandin E2, leukotrienes E4 and B4, and 15-hydroxyeicosatetraenoic acid. The kinetics of leukotriene B4 release by excess C5b-8 was quantitated by radioimmunoassay. Leukotriene B4 release approached a maximum around 30 min, and C6 dose-response studies performed at 1 h showed that maximal levels of leukotriene B4 were detected over a range of sublytic C5b-9 attack. Maximal release of leukotriene B4 was also achieved by C5b-8 without further enhancement by addition of lytic doses of C9. Results indicate that sublytic attack of oligodendrocytes by complement induces release of lipid-derived inflammatory mediators.

Antigen-specific T cells can mediate demyelination in organotypic central nervous system cultures

To investigate a role for T lymphocytes in primary demyelination of central nervous system (CNS) tissue, antigen-specific T cell lines sensitized to myelin-associated and myelin-unrelated antigens were developed from SJL mice and tested on myelinated organotypic cultures of syngeneic spinal cord. Demyelination was assessed morphologically by electron microscopy. Antigen responsiveness and specificity, and the phenotypes of the cell lines, were determined by thymidine uptake (3H-TdR) assays and flow cytometry (FC), respectively. Although all T cell lines caused pathologic changes in myelin, the CNS-antigen-specific line induced the most pronounced effects. 3H-TdR uptake assays and FC showed that after three cycles of incubation in the presence of interleukin-2 (IL-2) or antigen, the T cell lines had increased specificity and responsiveness to the priming antigen and were enriched for the L3T4 (helper/inducer) phenotype. This represents the first direct demonstration of T-cell-mediated demyelination, supports a role for the helper/inducer subset in CNS lesion development, and may prove relevant to the human demyelinating disease multiple sclerosis.

Opsonization with antimyelin antibody increases the uptake and intracellular metabolism of myelin in inflammatory macrophages

In most demyelinating diseases, macrophages are believed to be active agents of myelin destruction. In experimental encephalomyelitis, these cells appear to strip off and ingest the myelin lamellae, and myelin debris has been observed within the cell body. We show here in vitro conditions in which rat peritoneal macrophages phagocytose and metabolize CNS myelin lipids. Purified rat myelin, prelabeled in vivo with [14C]acetate, was incubated with preimmune serum or rabbit antiserum to rat CNS myelin and added to macrophage monolayers. Myelin opsonized with antimyelin antibodies was more readily phagocytosed and metabolized by cultured macrophages than untreated myelin or that preincubated with preimmune serum. In the presence of macrophages, levels of myelin polar lipids and cholesterol decreased, whereas radioactive cholesterol ester and triglyceride accumulated. Up to five times as much radioactive cholesterol ester and about twice as much triglyceride accumulated in macrophage cultures containing antibody-treated myelin as in cultures fed preimmune serum-treated myelin or in those incubated with untreated myelin. Both the fatty acid and the cholesterol from cholesterol ester contained radioactive label; therefore, both were derived at least partly from the radioactive myelin lipid. Antiserum to myelin purified from peripheral nerve was almost as effective as that to CNS myelin in stimulating cholesterol metabolism, whereas antiserum to galactocerebroside was about 70% as active. Antiserum to basic protein had less effect, whereas antiserum to the myelin-associated glycoprotein and proteolipid protein was inactive. Of the polar lipids, ethanolamine phosphatide was most degraded in both the antiserum- and preimmune serum-treated myelin, with the diacyl form and plasmalogen form degraded about equally. These experiments indicate that myelin-specific antibodies in inflammatory CNS lesions may participate in and stimulate macrophage-mediated demyelination.

Transformation of cells of astrocyte lineage into macrophage-like cells in organotypic cultures of mouse spinal cord tissue

Phagocytic cells on the surface of the explants and their relationships to the surface were examined morphologically and immunocytochemically in organotypic cultures of mouse spinal cord tissue. Phagocytic cells were rounded, had smooth cytoplasmic surfaces and were occasionally closely apposed to underlying cells by junctional complexes. These cells contained dense bodies, vacuoles, smooth and coated vesicles, a few microtubules and bundles of intermediate filaments similar to astroglial filaments. The superficial layer of the explant which usually consisted of astroglial cell bodies and their processes, sometimes contained immature neuroepithelial cells with numerous free ribosomes, centrioles, Golgi apparatus, microtubules and infrequently, intermediate filaments. Overall, the cells resembled poorly differentiated astrocytes. Numerous dense bodies and coated vesicles were observed in some of these immature cells as well as in astrocytes in the surface layer of the explant. Cytoplasmic bridges between immature cells within the explant and phagocytic cells on the surface were observed. Immunocytochemistry revealed the presence of glial fibrillary acidic protein within these surface phagocytic cells. It thus appears that immature neuroepithelial cells of astrocytic lineage are capable of transforming into macrophage-like cells in organotypic culture.

Fine structure of astrocytic processes during serum-induced demyelination in vitro

Astrocytic changes were examined ultrastructurally during serum-induced demyelination in organotypic cultures of mouse spinal cord tissue. The myelin sheaths of most myelinated fibers showed myelin breakdown. Sheet-like astrocytic processes completely and closely surrounded the demyelinating fibers and frequently engulfed myelin fragments. These processes were virtually devoid of glial filaments or microtubules and contained flocculogranular material, round and elongated cisterns and glycogen granules. Penetration of the myelin sheath by astrocytic processes was only rarely found. The cell body of the astrocyte was never insinuated between the myelin sheath and the axon. No endocytosis of myelin droplets via coated pits on the surface of astrocytes was observed. In comparison with phagocytic mononuclear cells in vivo, astrocytes in vitro dispose of myelin debris less actively. Astrocytes in serum-induced demyelination probably play a nonspecific but fundamental role during degeneration in segregating damaged nerve fibers from surrounding neuronal elements.

Preliminary analysis of cell and serum-induced demyelination in vitro using a syngeneic system

Previous studies on immune-mediated demyelination in vitro have usually tested sera and lymphoid cells in heterologous systems. The present study involved the examination of CNS cultures of SJL/J mouse spinal cord exposed to sera and lymphoid cells isolated from animals of the same strain previously injected with syngeneic spinal cord homogenate (SSCH) to induce acute experimental autoimmune encephalomyelitis (EAE). Examination of treated versus control cultures by light and electron microscopy at varying time points after exposure showed that spleen cells from animals with EAE produced significant demyelination and oligodendroglial cell destruction. Lymph node cells and sera from the same animals showed the same type of demyelination without marked oligodendroglial cell damage. The degree of myelin damage induced by spleen cells and sera did not correlate with the clinical status of the animal but a slight positive correlation was noted with lymph node cells. Cells and sera from control animals did not induce significant demyelination. These results suggest that in this syngeneic mouse system, there was a differential effect among cells from spleens and lymph nodes, and serum. This syngeneic system might allow for more meaningful pathologic and genetic analyses of immune-mediated demyelination.

The organization of astrocytes in organotypic mouse spinal cord culture: an electron microscope study

The organization of astrocytes in myelinated culture of mouse spinal cord tissue was analysed ultrastructurally and compared with the pattern in vivo. Astrocyte cell bodies and their processes, connected by punctate adhesions and gap junctions, formed a continuous layer around the entire explant. Throughout the parenchyma, thin astrocytic processes penetrated the neuropil, separated neurons, and invested some synaptic complexes. Others formed flattened sheets and contacted directly with the basal surface of ependymal cells. In the absence of mesenchymal elements, astrocytes in vitro occasionally possessed fragments of basal lamina on the surface of the explant and around minute intercellular spaces. Except for an incomplete basal lamina, these findings indicate that astrocytes in vitro are organized in a manner essentially identical to the situation in vivo.

Canine distemper and experimental allergic encephalomyelitis in the dog: comparative patterns of demyelination

The pattern of virus-induced and allergic demyelinating encephalomyelitis in the dog were compared. The predominant pattern of myelin loss in canine distemper (CD) infection was focal, periventricular and was initially noninflammatory. In contrast, sensitization to myelin produced a uniform pattern of central nervous system (CNS) myelinolysis which was disseminated, inflammatory and perivascular. Ultrastructurally, virus-infected neuroglia participated in the demyelination in CD, whereas infiltrating haematogenous mononuclear cells predominated in the lesions of experimental allergic encephalomyelitis (EAE). Areas of predilection within the CNS differed, being influenced by viral spread in CD and by vascular factors in EAE. In CD, the paramyxovirus appears to play a central role in the process of demyelination. In contrast to EAE, however, these studies do not support the view that autoreactivity to myelin contributes to the pathogenesis of CD demyelinating encephalomyelitis.

Serum demyelinating factors in multiple sclerosis

Sera from 21 patients with multiple sclerosis were applied to myelinated spinal cord cultures and evaluated for demyelinating activity. Samples were collected at various times when patients were on or off therapy with myelin basic protein or prednisone or both, and at various stages of disease. Five of 31 serum samples from 17 patients exhibited demyelinating activity when tested in a 40% concentration in tissue culture nutrient medium. Four of the 10 serum samples taken from patients with active or remitting multiple sclerosis (2 samples from the same patient) were demyelinative; 1 of 21 sera collected during stationary periods of disease was positive. There was no correlation between serum demyelinating activity and the presence or absence of treatment. Sera positive for demyelinating activity failed to inhibit myelin formation in initially unmyelinated cerebellar cultures.

In vivo demyelination by antimyelin antibodies

Central nervous system (CNS) myelin-specific antiserum was capable of initiating primary demyelination within 24 h following injection into the dorsal column of guinea pig spinal cord. Control serum injected in the same manner did not produce demyelination. The demyelinating lesions occurred as focal linear plaques of completely denuded intact axons surrounded by partially demyelinated and myelinated normal axons. Antiserum-mediated demyelination was followed by mononuclear cell infiltration 7-10 days later. Ultrastructural examination revealed vesiculation of myelin followed by cleavage of myelin lamellae at the intraperiod line. Remyelination began between 7 and 10 days following injection and correlated well with clinical evidence of recovery. The results of this study point to the importance of circulating antimyelin antibodies in the pathogenesis of demyelinating encephalitis. The model represents an in vivo approach to the study of the pathogenesis of immune-mediated myelinolysis in demyelinating disorders like multiple sclerosis (MS), subacute sclerosing panencephalitis (SSPE), and canine distemper encephalitis (CDE).

Demyelination produced by experimental allergic neuritis serum and anti-galactocerebroside antiserum in CNS cultures. An ultrastructural study

Cultures of mouse cerebellum were exposed to sera from rabbits with experimental allergic neuritis induced by whole peripheral nerve immunization (WN-EAN) and to rabbit anti-galactocerebroside (GC) antisera, and were studied by electron microscopy. Both antisera produced almost identical demyelinative patterns. These consisted of large intramyelinic splittings, "smudged" changes of myelin, degeneration of oligodendrocytes, and phagocytosis of myelin by astrocytes, changes similar to those described after application of whole spinal cord-induced experimental allergic encephalomyelitis (WM-EAE) sera. In addition, patterns which have been considered more characteristic of in vivo demyelinative lesions have been found, susch as vesicular disruption of myelin lamellae and peeling off and phagocytosis of myelin by phagocytic mononuclear cells with electron dense cytoplasm. The morphologic similarities between demyelinative patterns in central nervous system (CNS) cultures induced by anti-GC antiserum and WN-EAN serum and WM-EAE serum, and the fact that elevated antibody titers to GC are found in sera from rabbits with WN-EAN and WM-EAE (Saida, et al., 1977), support the concept that anti-GC antibody is the major factor in the production of CNS demyelination in vitro by sera from rabbits with WN-EAN and WN-EAE.

Characterization of antioligodendrocyte serum

An antioligodendrocyte serum (AOS) has been raised in rabbits against preparations of isolated bovine oligodendrocytes. The antibody was assayed by two techniques. By complement fixation with isolated oligodendrocytes, the titer of the antibody was 1:64 to 1:128. By indirect immunofluorescence testing of oligodendrocyte suspensions and frozen brain sections, the titer of the AOS was 1:256 to 1:512. When unabsorbed AOS was used, immunofluorescent staining proved it specific for bovine oligodendrocytes in suspension and in sections, and for human oligodendrocytes in sections. In cell suspensions, the staining was membrane related and in sections, cytoplasmic. The oligodendrocyte staining could be totally removed by absorption of AOS against oligodendrocyte suspensions, whereas absorption against bovine myelin, bovine myelin basic protein, and bovine neurons did not affect the staining reaction. AOS also stsined Schwann cells, a property possible related to antigens shared with oligodendrocytes. It is concluded that AOS is specific for oligodendrocytes and can now be applied to fundamental and disease-rel

Multiple sclerosis: demyelination and myelination inhibition of organotypic tissue cultures of the spinal cord by sera of patients with multiple sclerosis and other neurological diseases

Sera from 44 patients with Multiple Sclerosis, of three patients with neurological syndromes compatible with Multiple Sclerosis, of 34 patients suffering from other neurological diseases and of 25 pregnant healthy young women were tested for their demyelinating activity in myelinated tissue cultures. In order to leave the investigators unprejudiced, all sera were coded and intermixed with controls of rabbit EAE serum which had a potent demyelinating capacity. Demyelination was graded (from 0--4), heat lability at 56 degrees C (complement dependency?) was also tested with each serum. Only demyelination of a degree of 2 and more, which was abolished by heating to 56 degrees C, was counted as positive. Six of the 44 sera from MS patients (13.6%), 19 of 37 sera from neurological patients and none of the healthy young women demyelinated. Thus, serum demyelination of tissue cultures seems to be a nonspecific indicator of chronic disease of the nervous system and is of considerable general neurological interest, but does not indicate a demyelinating disease. Myelination inhibition was not observed with any of the human sera tested for it.

Abnormal myelin maturation in vitro: the role of cerebrosides

Myelinating neonatal rat cerebellar explants were maintained for up to 130 days in vitro. Myelin fractions were extracted from explants of different ages and purified by density gradient centrifugation. Three fractions obtained were termed "light myelin", "heavy myelin" and "membrane fraction" and were deficient in glycolipids compared to myelin fractions prepared from 15-day-old rat cerebellum. The culture myelin has an apparently normal ultrastructure but may not be as stable as myelin with a normal glycolipid composition.

Tissue culture studies of demyelinating disease: a critical review

Tissue culture studies of human and experimental demyelinating diseases have demonstrated that sera from patients with multiple sclerosis reversibly demyelinate central nervous system cultures. Similar changes are evoked by sera from animals with experimental allergic encephalomyelitis induced by inoculation with whole central nervous system tissue but not by encephalitogenic myelin basic protein. Sera and buffy coat or lymph node cells from humans with idiopathic polyneuritis and animals with experimental allergic neuritis demyelinate cultures of peripheral nervous system tissue. While these studies have contributed to speculations about pathogenetic mechanisms of demyelinating diseases, including the role of both circulating antibodies and delayed hypersensitivity factors, a number of important questions remain unanswered. Among these are the identity of the antigens that evoke antimyelin antibodies and the precise relationship of serum or cellular antimyelin factors to the pathogenesis or clinical course of the demyelinating diseases. Further studies with this technique may provide more complete information about the role of immunological events in induction of disease.

Synthetic galactocerebrosides evoke myelination-inhibiting antibodies

Synthetic galactodihydrocerebrosides with widely different fatty acid components can evoke myelination-inhibiting antibodies in rabbits. Whether these are the only such haptens involved in experimental immunizations of other species or in spontaneous human diseases is not yet known.

About demyelinating properties of humoral antibodies in experimental allergic encephalomyelitis. In vivo and in vitro studies

In order to elucidate the role of humoral antibodies in the pathogenesis of myelin lesions in experimental allergic encephalomyelitis (EAE) a combined in vivo and in vitro study was done using rabbits immunized with the purified A1 basic protein. Rabbits injected with whole white matter were used for comparison. Demyelinating activity appeared in the rabbit sera 5 days after injection, as tested in myelinated organotypic tissue cultures. In spite of this no lesions of the myelin preceded the appearance of inflammatory cells in the living animals. In the spinal cord changes in vascular permeability, as revealed by leakage of Evans blue-albumin complex, appeared at the same time as the cells. In contrast to in vitro, the mere presence of circulating antibodies in vivo does not appear to be enough to cause structural changes of the myelin. Possible reasons for this discrepancy are discussed; it is emphasized that the inflammatory changes develope first in areas where the so-called blood-brain barrier to diffusion of proteins is lacking.

On the development of CNS lesions in natural canine distemper encephalomyelitis

Acute lesions within spinal cord white matter have been studied by light and electron microscopy in 3 dogs suffering from the acute form of canine distemper encephalomyelitis (CDE). Prominent features of these lesions were viral inclusions, giant cell formation, cellular degeneration, myelin breakdown and phagocytic activity by cells believed to be derived from local glia. The viral inclusions occurred in giant cells, many astrocytes, macrophages and occasional oligodendroglia. Only suggestions of active viral replication from cell membranes were present. On the basis of the above features, these CDE lesions were classed as being acute. Perivascular inflammation and parenchymal invasion by haematogenous cells were lacking. However, older, gliotic, demyelinated lesions were always associated with inflammation. The pattern of demyelination in acute CDE lesions differed from those seen in other conditions, in particular the autoimmune demyelinating diseases. In acute CDE lesions, individual fibres became separated from others by rings of cells, the processes of which systematically stripped the myelin from the outer layers of the sheath inwards until a naked segment of axon remained. Some of the macrophages were recognisable as astroglia. Elsewhere, unequivocal astrocytes containing myelin debris were common. The results suggest that inflammation in acute CDE lesions is not a primary event, and that viral invasion causes breakdown of tissue which is accompanied pari passu by myelin destruction. The latter might be related to the non-specific release of host factors (viz. hydrolytic enzymes) or humoral factors during the cellular degeneration. Local cells appeared to participate in the process of myelin phagocytosis. Overt inflammation and damage by haematogenous cells were features only of chronic lesions and have been described previously in studies on chronic CDE lesions. The results are interpreted in terms of their relevance to the study of human subacute sclerosing panencephalitis, of which CDE is considered the animal analogue, and multiple sclerosis, the paradigm of the human demyelinating diseases.

The penetration of fluorescein-conjugated and electrondense tracer proteins into Xenopus tadpole optic nerves following perineural injection

The permeability of Xenopus tadpole optic nerves to macromolecules was studied in order to evaluate the usefulness of this system for studying mechanisms of serum-induced CNS demyelination in vivo. Single injections of either horseradish peroxidase (HRP), ferritin or fluorescein-conjugated human IgG were injected around the right optic nerve and tadpoles were then sacrificed between 15 min and 48 h. Each of the tracers had penetrated the nerve parenchyma by 30 min. Entry of HRP and ferritin occurred mainly via extracellular clefts between adjacent astrocytic endfeet in the glia limitans region. A similar mode of passage was suggested for IgG. Once within the nerve, the tracers became rapidly associated with myelinated axons. HRP was also seen in the periaxonal space but did not directly penetrate the myelin sheath. By 24 h, extracellular localization of tracer was virtually absent with nearly all of the tracer now being concentrated in vesicles within astrocytic processes and perikarya. The distribution of the tracers was not confined to the optic nerve on the injected side; some was seen in adjacent cranial peripheral nerves and surrounding extraocular musculature. Also, tracers eventually penetrated the pial sheath of the contralateral optic nerve. The results of this study indicate that tadpole optic nerves are permeable to a wide range of macromolecules. Furthermore, the distribution of these tracers to nearby cranial peripheral nerves may provide an important opportunity for testing the differential effect of various substances on central and peripheral myelin sheaths.

The significance of perivascular infiltrations in multiple sclerosis

143 autopsy cases of multiple sclerosis (19 acute and 124 chronic cases) were analysed histologically for the extent of active demyelination and the degree of infiltration within and outside the demyelinating lesions and in the leptomeninges. The results were compared with the duration of the illness. Infiltrations were found in 60% of all cases but more often (74%) in those with active demyelination. Inflammatory lesions outside demyelinating foci were observed in 27% of the total, and in 80% of them active demyelination was present. Inflammatory lesions in the meninges were present in 41% of the total and in 80% of these were accompanied by active demyelination. The duration of illness correlated with decreasing severity of active demyelination and of perivascular infiltration. Patients treated with cortico-steroids and/or immunosuppressive substances showed no or only moderate inflammatory lesions. The duration of illness in both these groups was significantly longer than the average of untreated patients. The significance of these pathological findings for the CSF cytology in multiple sclerosis is discussed.

Vesicular disruption of myelin in autoimmune demyelination

A pattern of autoimmune demyelination in EAE and EAN has been described which was encountered consistently and was sometimes more common than the better known phenomenon of active stripping of myelin by macrophages. This pattern involved the rapid dissolution of myelin into a vesicular network which was later degraded by macrophages. It occurred early in the disease, was not accentuated perivascularly, and was usually associated with the presence of macrophases. The underlying mechanisms are not known but several alternatives have been discussed, viz., activity of locally released antibody, cytotoxic factors, or hydrolytic enzymes.