Shark CNS myelin contains four polypeptides related to the PNS protein Po of higher classes

The relationship between the proteins of shark central nervous system (CNS) myelin and those of myelin from higher classes has been investigated using antibodies raised against a 31,500 molecular weight polypeptide from shark myelin. The antibodies cross-reacted with 3 shark CNS polypeptides apart from the original antigen, with 2 major polypeptides from shark peripheral nervous system myelin, with the Po protein from chicken and sheep peripheral nervous system myelin, but with none of the components of bovine CNS myelin. It appears that the oligodendroglial cells of the shark synthesize a protein closely related to the Po protein produced by Schwann cells of vertebrate classes above and including chondrichthytes.     

The species distribution of nervous system antigens that react with anti-myelin-associated glycoprotein antibodies

The reactivity of monoclonal and polyclonal antibodies directed against human central nervous system (CNS) myelin-associated glycoprotein (MAG) was investigated in a number of animal species. The antibodies included mouse monoclonal antibodies obtained by immunization with human MAG; HNK-1, a mouse monoclonal antibody raised against a human lymphoblastoma and used to identify a subset of lymphocytes with natural killer function; human IgM paraproteins associated with neuropathy; and polyclonal antibodies obtained from rabbits immunized with rat or human MAG. Following polyacrylamide gel electrophoresis of CNS and peripheral nervous system (PNS) tissue from human, bovine, cat, rabbit, guinea pig, rat, mouse, frog, gold fish and chicken, proteins were electrophoretically transferred onto nitrocellulose. The immune-staining of electroblots showed distinct interspecies variation in the reactivity of the antibodies with MAG. In addition, the species distribution of several low molecular weight glycoproteins present in PNS tissue that cross-react with anti-MAG antibodies was determined. These low molecular weight antigens are not present in CNS homogenates or in purified human CNS myelin. It was also shown that IgM from a patient with peripheral neuropathy and paraproteinemia associated with anti-MAG antibodies recognized these low molecular weight antigens. The results suggest that IgM paraproteins, HNK-1 and some mouse monoclonal antibodies react with carbohydrate determinants shared by MAG and several lower molecular weight glycoproteins present only in human, bovine, cat and chicken PNS. Rabbit polyclonal anti-rat MAG antisera and mouse monoclonal antibodies reacting with peptide epitopes of MAG are much more specific for detecting MAG than antibodies reacting with carbohydrate epitopes of human MAG. The results are discussed in relation to human demyelinating peripheral neuropathy associated with IgM paraproteinemia.     

Differential regulation of myelin phagocytosis by macrophages/microglia, involvement of target myelin, Fc receptors and activation by intravenous immunoglobulins.

Macrophages/microglia are the key effector cells in myelin removal. Differences exist in the amount and time course of myelin uptake in the central (CNS) and peripheral nervous system (PNS), the basis of this difference, however, is not yet clarified. In the present experiments we studied the phagocytosis rate of CNS or PNS myelin by macrophages and microglia in vitro. Additionally, the effects of intravenous immunoglobulins (IVIg) on this process were investigated. In the PNS experiments, sciatic nerves were cocultured with peritoneal macrophages. Optic nerve fragments were used to characterize the myelin-removing properties of microglia. Cocultures with peritoneal macrophages aimed at investigating the differences in phagocytosis between resident microglia and added macrophages. The myelin phagocytosis in sciatic nerve fragments was higher than in optic nerves, indicating differences in the myelin uptake rate between peripheral macrophages and microglia. IVIg increased the phagocytosis of PNS myelin by macrophages, but not by microglia in optic nerves. The addition of peritoneal macrophages to optic nerve fragments did not lead to an increase in the phagocytosis of CNS myelin either. The IVIg induced phagocytosis of PNS myelin by peripheral macrophages was associated with an increased expression of macrophage Fc receptors measured by FACS. Blocking of Fc receptors by anti-Fc receptor antibody reduced the IVIg induced PNS myelin phagocytosis to basic levels, indicating that the induced but not the basic myelin uptake by macrophages is Fc receptor dependent. In contrast to peripheral macrophages, IVIg did not increase Fc receptor density on microglia. These data indicate that phagocytosis of PNS and CNS myelin by macrophages or microglia is differentially regulated. Local factors within the CNS or PNS may affect this process by modulating the surface receptor profile and activation state of the phagocytic cell or the structure of the myelin sheath.     

Induction of anti-myelin antibodies in EAE and their possible role in demyelination.

Experimental allergic encephalomyelitis is characterized by invasion of lymphocytes and macrophages into the central nervous system resulting in inflammation, edema, and demyelination. Sera from Lewis rats from 7-95 days after immunization with purified guinea pig CNS myelin were examined with respect to their ability to opsonize myelin. This was correlated with the appearance of antibody components and the relative amounts of antibody to myelin basic protein (MBP) and proteolipid protein (PLP). Sera from rats 10-95 days after immunization preincubated with purified myelin induced phagocytosis of myelin by cultured macrophages with the resulting production of cholesterol ester. This opsonization activity as measured by the percentage of cholesterol esterified reached a peak at 26-27 days after immunization but remained significantly elevated up to 95 days post-immunization compared to the activity of serum from the Freund's adjuvant-injected controls. Immunoblots of the sera revealed a gradual increase in antibody activity against myelin components. ELISA assays for MBP and PLP antibody showed a similar pattern. Antibody to galactocerebroside (GC) was not detected by immunostains nor by the ELISA assay. Areas of demyelination were observed histologically by luxol-fast blue stained spinal cords up to 60 days post-immunization. These results indicate that antibodies to myelin protein when given access to myelin through or within the blood brain barrier could initiate or enhance the phagocytic response by peripheral or resident macrophages.     

Detection of antibodies to central nervous system antigens by solid phase radioimmunoassay

A solid phase radioimmunoassay is described which employs 125I-protein-A to detect the presence of antibodies against a panel of cellular and soluble central nervous system (CNS) specific antigens coated onto polyvinylchloride Microtiter plates. Serum antibodies from rabbits immunized against myelin, myelin basic protein (MBP), glial acidic fibrillary protein (GFAP), astroglioma cells, and cerebellar cells were easily detected, and high specificity for each antiserum and antigen was also demonstrable. The assay is applicable to cerebrospinal fluid (CSF) from patients with neurological diseases to detect antibodies against CNS-specific antigens. The assay should be useful for examining cell lines derived from CNS tissue for the presence of brain proteins.     

Characterization of CD8-positive macrophages infiltrating the central nervous system of rats with chronic autoimmune encephalomyelitis

CD8+ macrophages appear in the central nervous system (CNS) under various pathological conditions such as trauma and ischemia. Furthermore, macrophages expressing CD8 were found in CNS lesions of chronic, but not acute, experimental autoimmune encephalomyelitis (EAE). To further characterize cells with this phenotype, we examined CD8+ macrophages/monocytes in the CNS and peripheral organs during the course of acute and chronic EAE that had been induced by immunization of rats with myelin basic protein and myelin oligodendrocyte glycoprotein, respectively. Counting CD8+ macrophages in CNS lesions revealed that their numbers increased reaching about 60% of total infiltrating macrophages in chronic EAE, while CD8+ macrophages remained less than 5% throughout the course of acute EAE. Unexpectedly, however, higher abundance of CD8+ monocytes/macrophages in the peripheral blood was found in both acute and chronic EAE. Real-time polymerase chain reaction analysis revealed no significant difference in the levels of chemokines and chemokine receptors of blood CD8+ monocytes between acute and chronic EAE. mRNA expression of perforin, a cytotoxic substance, was up-regulated in CD8+ monocytes compared with that of CD8- monocytes in both acute and chronic EAE. These findings suggest that activated CD8+ macrophages may play a cytotoxic role in chronic EAE lesions and that cells other than CD8+ monocytes/macrophages determined the difference in CNS pathology between acute and chronic EAE. Analysis of CD8+ monocytes/macrophages may provide useful information to permit further dissect the pathomechanisms of multiple sclerosis and to develop effective immunotherapies against autoimmune diseases in the CNS.     

Identification of antibodies in anti-CNS and anti-PNS myelin sera by immunoblot, characterization by immunohistochemistry, and their effect in tissue culture

Immunoblot analysis of antiserum to rat central nervous system (CNS) myelin revealed antibodies to myelin basic protein (MBP), proteolipid protein (PLP), and numerous high molecular weight proteins. In addition, anti-CNS myelin serum exclusively immunostained 4 basic proteins of rat peripheral nervous system (PNS) myelin. Similarly, anti-PNS myelin sera immunostained many high molecular weight proteins in both CNS and PNS myelin in addition to P0 and 4 basic proteins. Purified MBP and PLP were immunostained by anti-CNS myelin sera and MBP and P0 by anti-PNS myelin sera, indicating that antigenic sites are preserved during protein purification. Immunohistochemical localization with antisera was confined to the myelin sheath except that antisera to CNS myelin also stained oligodendrocytes during the active period of myelination. While anti-CNS myelin sera specifically demyelinated centrally myelinated fibers in culture, none of the anti-PNS myelin sera used here demyelinated organotypic spinal cord-dorsal root ganglion cultures.     

T cell immunity and interferon-gamma secretion during experimental allergic encephalomyelitis in Lewis rats.

An immunospot assay that detects single secretory cells was used to enumerate interferon-gamma secreting cells (IFN-gamma-sc) in mononuclear cell suspensions from the central nervous system (CNS) and peripheral lymphoid organs after actively induced experimental allergic encephalomyelitis (EAE) in Lewis rats. In the CNS compartment there was a significant increase in the number of IFN-gamma-sc preceding the onset of the clinical signs of EAE. Both in rats with EAE and rats immunized with Freund's complete adjuvant (FCA) the number of IFN-gamma-sc increased in peripheral lymphoid organs, as compared to non-immunized controls. In view of the potent immunoregulatory effects of IFN-gamma, its intra-CNS secretion may play a crucial role for clinicopathological events in EAE. To study the numbers of primed T cells that in response to myelin antigens produced IFN-gamma, mononuclear cell suspensions from peripheral lymphoid organs were precultured to allow for antigen uptake, presentation and T cell triggering, followed by enumeration of IFN-gamma-sc. T cells responding to a peptide of myelin basic protein (MBP) that previously have been shown encephalitogenic in Lewis rats, appeared initially and were quantitatively dominant over the course of EAE. Later, T cell reactivities to multiple regions of MBP appeared, showing that the concept of immunodominance in EAE is non-absolute and time dependent. Splenocyte cultures from EAE rats exposed to the different antigens showed a reduced number of IFN-gamma-sc compared to cultures not exposed to antigen, suggesting an antigen-induced suppression of T cell effector molecules.     

Effects of autoimmunity on recovery of function in adult rats following spinal cord injury

The central nervous system (CNS) is considered to be an immune-privileged site. For a long time, autoimmunity-induced inflammation has been viewed as an important mediator of secondary damage in the CNS following injury. However, other studies also suggest that autoimmunity is protective and beneficial. To investigate whether protective autoimmunity is present following spinal cord injury (SCI), we employed neonatally thymectomized (Tx) rats which contain few T lymphocytes in their peripheral blood, and passively immunized them with T lymphocytes activated by myelin basic protein (MBP) or spinal cord homogenate (SCH). Here we report that, among Tx, sham-Tx (sTx) and normal rats that received a contusive SCI, no significant histological and behavioral differences were found, suggesting that the endogenous T lymphocytes had no significant influence on the pathogenesis of secondary SCI. In rats passively immunized with MBP- or SCH-activated T cells (MBP-T or SCH-T, respectively), similar numbers of CD4⁺ T cells were found to infiltrate into the injured spinal cords. However, only the MBP-T immunization showed neuroprotection, evidenced by the reduction of post-traumatic neuronal losses and improvement of functional recovery. These results collectively suggest that not all T lymphocytes against CNS antigens are neuroprotective and that a subpopulation of them, such as those of MBP-T cells, could be beneficial for SCI repair.     

Microglia and macrophage activation and the regulation of complement-receptor-3 (CR3/MAC-1)-mediated myelin phagocytosis in injury and disease

Microglia and macrophages play critical roles in the response of the central and peripheral nervous systems (CNS and PNS, respectively) to injury and disease, one of which is the removal of degenerated myelin by phagocytosis. Myelin removal is efficient during Wallerian degeneration, which follows injury to PNS axons, and in CNS autoimmune demyelinating diseases (e.g., multiple sclerosis) but is inefficient after injury to CNS axons. We suggest that inefficient myelin removal results from deficient microglia activation, reflected by the failure to up-regulate Galectin-3/MAC-2 expression, which marks a state of activation correlated with efficient myelin phagocytosis. Surprisingly, whether or not executing myelin phagocytosis, CNS microglia express the alphaM/beta2 integrin complement receptor-3 (CR3/MAC-1), which has the potential of mediating efficient myelin phagocytosis. We hypothesize that CR3/MAC-1 might be present in distinct inactive and active states that determine, respectively, efficient and inefficient CR3/MAC-1-mediated myelin phagocytosis. We present evidence that CR3/MAC-1-mediated myelin phagocytosis is regulated in microglia and macrophages. First, CR3/MAC-1- mediated myelin phagocytosis has complement-dependent and -independent components. Second, an active complement system augments CR3/MAC-1-mediated myelin phagocytosis. Third, anti-alphaM monoclonal antibodies (MAbs) inhibit and anti-beta2 MAbs augment CR3/MAC-1-mediated myelin phagocytosis in the presence and absence of an active complement system. Fourth, an active complement system modulates MAb-induced regulation of CR3/MAC-1-mediated myelin phagocytosis. Overall, MAb-induced phagocytosis regulation might range three- to sevenfold from inefficient to efficient. We suggest that one of the mechanisms underlying MAb-induced phagocytosis regulation is the induction/stabilization of inactive and active conformational changes. Monoclonal antibody-induced phagocytosis regulation must reveal a mechanism by which native extracellular molecules bind to and regulate CR3/MAC-1-mediated myelin phagocytosis in microglia and macrophages.     

Microheterogeneity of anti-myelin-associated glycoprotein antibodies

Antibodies to the myelin-associated glycoprotein (MAG) are implicated in the pathogenesis of an acquired demyelinating polyneuropathy. We studied IgM affinity to MAG in 18 patients with anti-MAG antibodies. Binding of sera was tested for anti-MAG immunoreactivity in central nervous system (CNS) by ELISA and in CNS and peripheral nervous system (PNS) by Western blot analysis. Furthermore, immunohistochemical characterization of IgM binding on sural nerve tissue was investigated using the indirect peroxidase method. Western blot analysis revealed that all sera detected MAG in central myelin, but only eight in peripheral myelin. Anti-MAG-IgM-ELISA-titers correlated significantly (p<0.0001) with PNS-Western blot results. By indirect immunoperoxidase immunohistochemistry, 12 sera stained myelin sheaths, while 6 sera showed no staining. These results demonstrate considerable variations in antibody binding strength to MAG between PNS myelin and CNS myelin. The relevance of these differences for the pathogenesis of the neuropathy and clinical impairment remains to be demonstrated.     

Proteolipid DM-20 predominates over PLP in peripheral nervous system.

The major central nervous system (CNS) myelin proteolipid (PLP) is also expressed in the peripheral nervous system (PNS). This paper gives evidence that DM-20, an isoform of PLP, also occurs in rat sciatic nerves, where, in contrast to what is seen in CNS myelin, it predominates over PLP. This conclusion was reached on the basis of results obtained by immunoblot analysis of a crude proteolipid extract from adult peripheral nerve with two site-specific anti-proteolipid (PLP and DM-20) antibodies. This finding was further corroborated by characterization of the products obtained by Polymerase Chain Reaction (PCR) amplification of cDNAs synthesized from total RNA of 14-day-old sciatic nerves. The significance of the occurrence of these proteolipids in PNS remains obscure.     

Myelin basic protein in lipid-bound form induces experimental allergic encephalomyelitis and demyelination in Lewis rat.

Myelin basic protein (MBP) was isolated from guinea-pig spinal cord in a form retaining the binding to all the myelin lipids. This new, lipid-bound and native-like preparation was used to immunize Lewis rats in complete Freund's adjuvant (CFA) in order to produce experimental allergic encephalomyelitis (EAE). The clinical features were compared with those of Lewis rats immunized with lipid-free MBP (LF-MBP), myelin, LF-MBP + octyl-POE (the non-ionic detergent used for the purification of LB-MBP) and octyl-POE alone. The clinical observation indicate that LB-MBP exerts an encephalitogenic activity on Lewis rats which is more intense than LF-MBP and includes demyelinating lesions in the central nervous system (CNS). The data suggest that LB-MBP is a new encephalitogenic antigen, which may induce more intensive immunization in rats and may be relevant in humans for autoimmune demyelinating diseases of the CNS.     

Peripheral nerve demyelination induced by intraneural injection of experimental allergic encephalomyelitis serum.

Intraneural injection of sera from rabbits with experimental allergic encephalomyelitis, induced by sensitization with bovine brain white matter in complete Freund's adjuvant, produced focal primary demyelinative lesions in rat sciatic nerves. Demyelinating activity was removed by prior incubation of antisera with central (CNS) and peripheral nervous system (PNS) myelin but not with liver or kidney, and was heat-labile and complement-dependent. Recipient animals developed a sensorimotor disturbance of their toes and ankles on the side injected with antiserum. Twenty minutes after antiserum injection, Schwann cells showed focal cytoplasmic outpouching and their external mesaxons opened. Between 1 and 8 hours after injection vacuolation, splitting and vesiculation of myelin became increasingly prominent at Schmidt-Lanterman clefts and paranodal regions, with concomitant degenerative changes in Schwann cell cytoplasm. Polymorphonuclear cell infiltration and endoneurial edema were apparent at this time. Substantial demyelination occurred before the appearance of phagocytic cells. Between 8 hours and 3 days many nerve fibers were surrounded and attacked by invading macrophages. Axons became demyelinated progressively over several internodes by macrophage phagocytosis. Early signs of remyelination were observed by 5 days. These findings suggest that antibodies directed against antigens common to both CNS and PNS myelin can produce in vivo peripheral nerve demyelination.     

IgM and IgG responses during chronic relapsing experimental allergic encephalomyelitis (r-EAE)

During chronic relapsing experimental allergic encephalomyelitis (r-EAE) in guinea pigs, serum IgM and IgG concentrations increased markedly early in disease. Serum IgM and IgG increased similarly in control animals immunized with Freund's incomplete adjuvant (FIA) and Mycobacterium tuberculosis (MT). In the chronic phase of r-EAE but not in control animals, elevated IgM was also found in central nervous system (CNS) extracts, suggesting intrathecal IgM synthesis. IgG antibodies against myelin and myelin basic protein (MBP) were regularly detected in r-EAE sera from day 21 post inoculation (p.i.), reaching maximum levels in the early chronic phase. IgG antibodies against galactocerebroside (GC) and galactose appeared in some r-EAE sera. Oligoclonal IgG bands were demonstrated in all r-EAE guinea pig sera 21-26 days p.i. The bands in serum decreased in number and strength in the chronic phase. They could be traced to antibodies against MT in 4 of 10 animals, but not to antibodies against myelin, MBP, GC or galactose. Oligoclonal IgG bands were also regularly visualized in r-EAE CNS 124 days p.i., suggesting persistent intrathecal IgG synthesis. They varied in number and migration between different regions of individual CNS. Oligoclonal CNS IgG was related to antibodies against MT in only one of 7 animals, and in no case to antibodies against myelin.     

Myelination in cerebellar slice cultures: Development of a system amenable to biochemical analysis

Myelin deposition and maintenance are critical to proper function of the mammalian nervous system. Previous investigations of myelination in the central nervous system (CNS) were hampered by the lack of an in vitro system that can faithfully reproduce in vivo events yet is amenable to biochemical investigation. We have developed a procedure, based on organotypic cultures, which permits efficient preparation of large numbers of cerebellar slice cultures that can be easily manipulated. Cultures have been examined to document myelination biochemically (by incorporation of [³⁵S] sulfate into sulfolipids), immunohistochemically (by labeling the myelin components myelin basic protein and galactocerebroside), and morphologically (by both light and electron microscopy). We tested the effects of biologically active peptides and antibodies on myelination in the thin slices. The results indicate that the cultures provide an in vitro system that can be used to examine specific cellular events that occur during CNS myelination. © 1993 Wiley-Liss, Inc.     

Antibodies to P2 and P1 myelin antigens in experimental allergic neuritis and allergic encephalomyelitis

We confirmed earlier observations that experimental allergic neuritis (EAN) in Lewis rats induced by injection of bovine peripheral nerve myelin in complete Freund's adjuvant is not accompanied by development of experimental allergic encephalomyelitis. However, sera of these animals contained elevated titers of antibodies against central nervous system myelin basic protein (BP), likely induced by peripheral nerve P1 protein. Anti-BP antibodies were not seen in sera of rats with EAN induced by peripheral nerve P2 protein. Lack of encephalogenicity of bovine myelin in Lewis rats does not reflect simply lack of immune responses induced against BP.     

The use of protease inhibitors in experimental allergic neuritis.

In experimental allergic neuritis (EAN) break-down of myelin is attributed to macrophages, which among other factors contain and secrete proteases. In vitro studies have shown that cathepsin D, an acidic aspartyl endopeptidase, and plasmin can degrade myelin proteins. In order to elucidate a potential therapeutic effect of protease inhibitors we treated Lewis rats, immunized with bovine peripheral nervous system myelin, with epsilon-amino-caproic acid (EACA) or pepstatin. EACA or pepstatin was administered twice daily by intraperitoneal injection beginning on day 6 postimmunization or from the onset of disease (on day 12) through day 24. Compared to saline-treated controls, animals treated with either of the inhibitors showed delayed development of clinical signs and electrophysiological abnormalities. Maximal severity and the further course of disease, however, were not different in control and treated groups. Immunohistological evaluation of sciatic nerve specimens on day 24 postimmunization showed equal numbers of cells positive for ED1 (macrophages) and cathepsin D in all animal groups. There was also no difference in the spontaneous proteolytic activity of the sciatic nerve homogenates at pH 2.8, 5.0, and 7.4. Incubation of the homogenates with pepstatin, however, significantly reduced proteolytic activity at pH 2.8 and 5.0, while EACA had no effect at any pH tested. These results imply that treatment to limit the infiltration of cathepsin D-positive cells or to reduce the induction or activity of cathepsin D may provide a therapeutic avenue for treating inflammatory demyelination of the peripheral nervous system.     

Focal experimental autoimmune encephalomyelitis in the lewis rat induced by immunization with myelin oligodendrocyte glycoprotein and intraspinal injection of vascular endothelial growth factor

Various models of experimental autoimmune encephalomyelitis (EAE) have led to insights into the pathogenesis and novel therapies for multiple sclerosis. One generalized EAE model uses immunizing the Lewis Rat with myelin oligodendrocyte glycoprotein (MOG) and complete Freund's adjuvant that induces systemic disease and inflammatory lesions at random central nervous system (CNS) locations. These lesions result from a combination of sensitized T cells and pathogenic antibodies gaining access to the CNS to cause an immune assault on myelin‐expressing oligodendrocytes. We report a focal and temporal variant of the EAE model that results in immune‐mediated demyelination at a predictable time and location. Lewis rats were immunized with the extracellular domain (1‐125) of recombinant rat MOG in incomplete Freund's adjuvant (IFA) to induce a clinically silent humoral response. Vascular endothelial growth factor (VEGF) was then microinjected into the spinal cord to induce a transient, focal breakdown of the blood brain barrier (BBB). Clinical signs were apparent within 72 hours and began to resolve by day 21. The histopathology at the site of injection consisted of a focal region containing OX‐42⁺ cells, phagocytic cells with debris, extensive demyelination, and some lymphocyte infiltration. Neither intraspinal injection of PBS into immunized animals nor VEGF into animals treated with IFA alone resulted in clinical lesions. Thus, a transient, focal opening of the BBB with VEGF in animals with subclinical MOG immunization leads to a discrete inflammatory demyelinating lesion. This model may be useful for the study of transplanted myelin‐forming cells in a discrete inflammatory demyelinating lesion. © 2010 Wiley‐Liss, Inc.     

Autoimmunity against myelin oligodendrocyte glycoprotein is dispensable for the initiation although essential for the progression of chronic encephalomyelitis in common marmosets

To elucidate the pathogenetic significance of myelin/oligodendrocyte glycoprotein (MOG)-specific autoreactivity in a genetically and immunologically heterogeneous nonhuman primate model of multiple sclerosis, we analyzed experimental autoimmune encephalomyelitis (EAE) in the outbred common marmoset (Callithrix jacchus). One sibling each of 5 bone marrow chimeric marmoset twins was immunized with myelin derived from wild-type (WT) C57BL/6 mice (WT myelin); the other sibling was immunized with myelin from MOG-deficient C57BL/6 mice (MOG -/- myelin). One twin pair developed acute EAE simultaneously; the 4 remaining twin siblings immunized with WT myelin developed chronic progressive EAE, whereas siblings of these 4 monkeys remained free of clinical disease signs. Many EAE-related abnormalities were identified in the CNS of both groups by magnetic resonance imaging and histologic analysis, but mean percentages of spinal cord demyelination were lower in monkeys immunized with MOG -/- myelin (8.2%) than in WT myelin-immunized animals (40.5%). There was a strong correlation between the development of overt clinical EAE and seropositivity for anti-MOG antibodies, but blood and lymph node T-cell proliferative responses showed no relationship to disease. These results indicate that the initiation of CNS inflammation and demyelination can take place in the absence of detectable autoimmunity against MOG, but the clinical progression and histopathologic severity depends on the presence of antibodies against MOG in this multiple sclerosis model.