Antibodies to myelin components are routinely detected in multiple sclerosis patients. However, their presence in some control subjects has made it difficult to determine their contribution to disease pathogenesis. Immunization of C57BL͞6 mice with either rat or human myelin oligodendrocyte glycoprotein (MOG) leads to experimental autoimmune encephalomyelitis (EAE) and comparable titers of anti-MOG antibodies as detected by ELISA. However, only immunization with human (but not rat) MOG results in a B cell-dependent EAE. In this study, we demonstrate that these pathogenic and nonpathogenic anti-MOG antibodies have a consistent array of differences in their recognition of antigenic determinants and biological effects. Specifically, substituting proline at position 42 with serine in human MOG (as in rat MOG) eliminates the B cell requirement for EAE. All MOG proteins analyzed induced high titers of anti-MOG (tested by ELISA), but only antisera from mice immunized with unmodified human MOG were encephalitogenic in primed B cell-deficient mice. Nonpathogenic IgGs bound recombinant mouse MOG and deglycosylated MOG in myelin (tested by Western blot), but only pathogenic IgGs bound glycosylated MOG. Only purified IgG to human MOG bound to live rodent oligodendrocytes in culture and, after cross-linking, induced repartitioning of MOG into lipid rafts, followed by dramatic changes in cell morphology. The data provide a strong link between in vivo and in vitro observations regarding demyelinating disease, further indicate a biochemical mechanism for anti-MOGinduced demyelination, and suggest in vitro tools for determining autoimmune antibody pathogenicity in multiple sclerosis patients. multiple sclerosis ͉ experimental autoimmune encephalomyelitis ͉ lipid rafts ͉ B cell-deficient mice ͉ encephalitogenicity M ultiple sclerosis (MS) is a chronic demyelinating disease of the central nervous system (CNS) in which both T cells and antibodies against myelin antigens are routinely detected (1, 2). B cell responses in MS pathogenesis are implicated by the presence of Ig deposits and myelin debris in demyelinating lesions (3-8), and the observation that plasma exchange dramatically reduces clinical disease in a subset of patients (9). Of particular interest to the present study, antibodies to myelin oligodendrocyte glycoprotein (MOG) are detected in the sera and plaques of MS patients (10), and thus are possible predictors of disease progression (11). However, because some control subjects can also harbor anti-myelin antibodies (1, 2, 12), their contribution to MS pathogenesis has been controversial and difficult to identify in individual patients. Further complicating the issue, MS may be several diseases of differing etiologies (5), whereby anti-myelin antibodies may be pathogenic in some forms of MS but merely a reflection of tissue damage in others. Thus, an understanding of whether anti-myelin antibodies are in fact pathogenic, and if so, by what mechanisms they operate, could provide important information for novel diagnosti...

Myelin is a dynamic, functionally active membrane necessary for rapid action potential conduction, axon survival, and cytoarchitecture. The number of debilitating neurological disorders that occur when myelin is disrupted emphasizes its importance. Using highresolution 2D gel electrophoresis, mass spectrometry, and immunoblotting, we have developed an extensive proteomic map of proteins present in myelin, identifying 98 proteins corresponding to at least 130 of the Ϸ200 spots on the map. This proteomic map has been applied to analyses of the localization and function of selected proteins, providing a powerful tool to investigate the diverse functions of myelin.M yelin is a dynamic, functionally active membrane (1), the loss or damage of which results in serious neurological disorders including leukodystrophies, central and peripheral neuropathies, and inflammatory demyelinating diseases such as multiple sclerosis (2-4). Rapid and efficient action potential conduction in the nervous system depends on myelin, which traditionally has been viewed as a passive contributor to conduction by increasing internodal membrane resistance and decreasing membrane capacitance (5). However, recent work has revealed additional active roles for myelin in nervous system development and function. For example, myelin regulates axon diameter and the formation of axon microtubular networks, and it is a key player in ion channel clustering at nodes of Ranvier (6-11). In return, the axon regulates myelin gene expression (12) and oligodendrocyte survival (13). The functional coupling of myelin and axons is further illustrated by the transfer of phospholipids (14) and N-acetylaspartate (15) from the axon to the myelin sheath.A major impediment to understanding the active biological functions of myelin is the relative lack of myelin proteins that have been described and characterized. Thus, we have undertaken an extensive proteomic analysis of central nervous system myelin, developed a 2D PAGE map of myelin proteins, identified 98 of these proteins, and illustrated the power and utility of this approach through specific applications of comparative proteomics. For example, a comparison of CNS and peripheral nervous system (PNS) myelin proteins has revealed a previously undescribed component of Schwann cell microvilli, a proteomic matching of myelin from normal and genetically modified mice lacking key myelin lipids has demonstrated a dramatic reduction of two newly recognized myelin protein kinases, and an application of the map to a neuroimmunological analysis of demyelinating disease has identified a signaling mechanism (16).

Myelin oligodendrocyte glycoprotein (MOG) is, quantitatively, a relatively minor component of the myelin membrane. Nevertheless, peritoneal administration of MOG evokes potent cellular and humoral immunoreactivity, resulting in an experimental allergic encephalitis with immunopathology similar to multiple sclerosis. Moreover, antibodies against MOG cause myelin destruction in situ. Therefore, it appears that MOG-related demyelination is dependent on anti-MOG antibody, but the mechanism(s) by which it occurs is unclear. Of potential significance are observations that some proteins are selectively partitioned into specialized plasma membrane microdomains rich in glycosphingolipids and cholesterol ("lipid rafts"). In particular, during ligand or antibody cross-linking, various plasma membrane receptors undergo enhanced partitioning into rafts as an obligatory first step toward participation in early signal transduction events. In contrast to mature myelin, in oligodendrocytes (OLs) in culture MOG is not raft associated [Triton X-100 (TX-100) soluble, 4 degrees C]. However, in this study we show that antibody cross-linking (anti-MOG plus secondary antibody) of MOG on the surface of OLs results in the repartitioning of approximately 95% of MOG into the TX-100-insoluble fraction. This repartitioning of MOG is rapid (

Antibody-induced demyelination is an important component of pathology in multiple sclerosis. In particular, antibodies to myelin oligodendrocyte glycoprotein (MOG) are elevated in multiple sclerosis patients, and they have been implicated as mediators of demyelination. We have shown previously that antibody crosslinking of MOG in oligodendrocytes results in the repartitioning of MOG into glycosphingolipid-cholesterol membrane microdomains ("lipid rafts"), followed by changes in the phosphorylation of specific proteins, including dephosphorylation of ␤-tubulin and the ␤ subunit of the trimeric G protein and culminating in rapid and dramatic morphological alterations. In order to further elucidate the mechanism of anti-MOG-mediated demyelination, we have carried out a proteomic analysis to identify the set of proteins for which the phosphorylation states or expression levels are altered upon anti-MOG treatment. We demonstrate that treatment of oligodendrocytes with anti-MOG alone leads to an increase in calcium influx and activation of the MAPK/Akt pathways that is independent of MOG repartitioning. However, further cross-linking of anti-MOG⅐MOG complexes with a secondary anti-IgG results in the lipid raft-dependent phosphorylation of specific proteins related to cellular stress response and cytoskeletal stability. Oligodendrocyte survival is not compromised by these treatments. We discuss the possible significance of the anti-MOG-induced signaling cascade in relation to the initial steps of MOG-mediated demyelination.The investigation of the transfer of information between myelin and axons is at the forefront of myelin biology and demyelinating disease (1-3). Loss or damage of myelin, such as occurs in the human demyelinating disease multiple sclerosis, results in axonal degeneration with severe, generally irreversible, functional consequences (4). Multiple sclerosis-related demyelination is in part induced by antibodies directed against surface antigens of myelin and oligodendrocytes (OLs), 1 the myelin-producing cells of the central nervous system (5). In particular, antibodies to myelin oligodendrocyte glycoprotein (MOG), a highly encephalitogenic glycoprotein concentrated in the outer lamella of the myelin sheath and thus exposed to the environment (6), have been implicated as mediators of demyelination (7-10).Upon ligand or antibody cross-linking, a variety of plasma membrane receptors undergo enhanced partitioning into glycosphingolipid-cholesterol membrane microdomains ("lipid rafts") as an obligatory first step toward participation in early signal transduction events (11-13). We have previously shown that antibody cross-linking of MOG on the surface of OLs results in the rapid repartitioning of a significant fraction of MOG into lipid rafts, followed by dephosphorylation of ␤-tubulin and the ␤ subunit of the trimeric G protein (G␤), and a rapid retraction of OL processes and myelin-like membranes (14). In order to elucidate this mechanism and better consider its relationship to antibody-mediated demyelina...