Myelin lipophilin-induced demyelinating disease of the central nervous system

Myelin basic protein in experimental allergic encephalomyelitis is not affected at the posttranslational level: implications for demyelinating disease

The microheterogeneity of myelin basic protein, expressed as the ratio between the least cationic (C-8) charge isomer and the most cationic (C-1), was examined in experimental allergic encephalomyelitis (EAE) cases. These included acute EAE of 2 months' duration induced with bovine proteolipid protein in complete Freund's adjuvant (CFA), chronic EAE induced with mouse spinal cord homogenate in varying doses from 0.5 to 2.0 mg in CFA, and chronic relapsing EAE of 12 months' duration induced with synthetic peptide 139-151 of the proteolipid protein sequence. The C-8/C-1 ratio was within the normal range for all groups of animals. However, the C-8/C-1 ratio was six- to sevenfold increased in a spontaneously demyelinating transgenic model, ND4, which contains 70 copies of the cDNA for DM20 (Mastronardi et al.: 1996). Since an increase in the C-8/C-1 ratio was also observed in victims of multiple sclerosis but not other neurological diseases, the ND4 model may address primary changes prior to demyelination, while the EAE model addresses the autoimmune aspects of the disease.

Minireview: autoimmune responses to myelin proteolipid protein

The authors present a brief historical sketch of the development of our understanding of immune responses to myelin proteolipid protein (PLP) and the acceptance of PLP as a potent antigen in the induction of experimental allergic encephalomyelitis (EAE). The distinct characteristics of the PLP molecule that may contribute to complex immune responses to this protein are reviewed and these responses are compared with those to MBP, both in the pathology of EAE and at the level of the T cell. Recent evidence demonstrating differences between T cell responses to PLP and MBP is reviewed. Finally, the potential contribution of immune responses to PLP in human diseases, particularly multiple sclerosis (MS), that have been identified to date are then summarized.

Peptide determinants of myelin proteolipid protein (PLP) in autoimmune demyelinating disease: a review

This article reviews recent advances in understanding the role of myelin proteolipid protein (PLP) in autoimmune demyelination. It is drawn largely from work published within the last ten years and discusses the immunology of PLP in the historical context of what has been learned from extensive studies on the immune response to myelin basic protein (MBP). Despite the fact that PLP is the major protein constituent of mammalian myelin, its role in autoimmune demyelination has not been widely recognized. The lack of understanding about the immunology of PLP is a direct result of the biochemical characteristics of the protein. PLP is a highly hydrophobic membrane protein with limited aqueous solubility. The hydrophobicity of PLP has thwarted immunologic studies of the intact protein. Recent work has circumvented the technical obstacles of studying the intact protein by using soluble synthetic PLP peptides. This approach has rapidly resulted in a more definitive understanding of the immune response to PLP. Presently, the data indicate that: i) PLP is a major central nervous system (CNS) specific encephalitogen; ii) CD4+ T cell reactivity to discrete PLP peptide determinants can mediate the development of acute, chronic relapsing, and chronic progressive experimental autoimmune encephalomyelitis (EAE); and iii) T cell reactivity to multiple PLP determinants occurs in patients with multiple sclerosis (MS), the major human CNS demyelinating disease.

The structure and function of central nervous system myelin

Multiple sclerosis (MS) is characterized by the active degradation of central nervous system myelin, a multilamellar membrane system that insulates nerve axons. MS arises from complex interactions between genetic, immunological, infective, and biochemical mechanisms. Although the circumstances of MS etiology remain hypothetical, one persistent theme involves immune system recognition of myelin-specific antigens derived from myelin basic protein, the most abundant extrinsic myelin membrane protein, and/or another equally suitable myelin protein or lipid. Knowledge of the biochemical and physical-chemical properties of myelin proteins, and lipids, particularly their composition, organization, structure, and accessibility with respect to the compacted myelin multilayers, thus becomes central to understanding how and why these antigens become selected during the development of MS. This article focuses on the current understanding of the molecular basis of MS as it may relate to the protein and lipid components of myelin, which dictate myelin morphology on the basis of protein-lipid and lipid-lipid interactions, and the relationship, if any, between the protein/lipid components and the destruction of myelin in pathological situations.

Autoreactive T and B cells responding to myelin proteolipid protein in multiple sclerosis and controls

The pathogenesis of multiple sclerosis (MS) could involve an autoimmune response to proteolipid protein (PLP). Immunization of experimental animals with this major myelin protein can lead to experimental allergic encephalomyelitis. To identify a possible role of PLP as target antigen in MS, we evaluated T cell immunity to PLP in blood and cerebrospinal fluid (CSF) from patients with MS and controls by counting cells which in response to PLP in short-term cultures secreted interferon-gamma. The PLP-specific B cell response was analyzed by counting cells secreting anti-PLP antibodies. PLP-reactive T cells were detected in blood of most MS patients (mean value 1 per 20,408 mononuclear cells), and at 41-fold higher numbers in CSF (mean 1 per 500 CSF cells). Anti-PLP IgG antibody-secreting cells were detected in blood from most MS patients (mean 1 per 30,303 cells), but such cells were 49-fold more frequent in CSF (mean 1 per 625 cells). PLP-reactive T and B cells were also detected in blood and CSF from control patients, but at much lower numbers. A strong and persistent autoimmune response to PLP as well as to other myelin proteins, enriched in CSF, is proposed to be pathogenetically important in MS.

Central nervous system myelin: structure, function, and pathology

Multiple sclerosis (MS) and a number of related distinctive diseases are characterized by the active degradation of central nervous system (CNS) myelin, an axonal sheath comprised essentially of proteins and lipids. These demyelinating diseases appear to arise from complex interactions of genetic, immunological, infective, and biochemical mechanisms. While circumstances of MS etiology remain hypothetical, one persistent theme involves recognition by the immune system of myelin-specific antigens derived from myelin basic protein (MBP), the most abundant extrinsic myelin membrane protein, and/or another equally susceptible myelin protein or lipid component. Knowledge of the biochemical and physical-chemical properties of myelin proteins and lipids, particularly their composition, organization, structure, and accessibility with respect to the compacted myelin multilayers, thus becomes central to the understanding of how and why these antigens become selected during the development of MS. This review focuses on current understanding of the molecular basis underlying demyelinating disease as it may relate to the impact of the various protein and lipid components on myelin morphology; the precise molecular architecture of this membrane as dictated by protein-lipid and lipid-lipid interactions; and the relationship, if any, between the protein/lipid components and the destruction of myelin in pathological situations.

Chronic experimental autoimmune encephalomyelitis in the guinea pig. Presence of anti-M2 antibodies in central nervous system tissue and the possible role of M2 autoantigen in the induction of the disease

Experimental autoimmune encephalomyelitis (EAE) can be transferred adoptively with T cells sensitized to the basic protein of myelin (BP). However, in the guinea pig, the chronic form of EAE has not been found to be inducible with BP alone, nor has it been adoptively transferred. An antibody response to the central nervous system (CNS) myelin autoantigens was looked for in serum and target CNS tissue in S13 guinea pigs with isologous CNS tissue-induced chronic EAE. Antibody activity was estimated by an immunoenzymatic technique and by autoradiography, using immunoprecipitated and electrophoresed relevant radiolabelled antigens. In serum, IgG antibody response to BP and M2 reached its maximum level 30 to 40 d after immunization and then declined progressively until it became undetectable. On the other hand, while anti-BP antibodies were seldom detected in CNS tissue acid extract, anti-M2 IgG antibodies were always present in CNS tissue of chronic EAE animals, and the amount of these antibodies were related to the severity of symptoms and lesions. No antibody response to proteolipid or to galactocerebroside was detected in serum or CNS tissue. BP-immunized controls showed no chronic EAE and no response to M2 in their serum or CNS tissue. Inasmuch as M2 has been shown to be a glycoprotein of CNS myelin, and anti-M2 antibodies to have a demyelinating property, the latter would be responsible for CNS tissue demyelination in chronic EAE. A shared role of BP and M2 in the induction of chronic EAE in the guinea pig is suggested.

Chronic-relapsing experimental allergic encephalomyelitis in strain-13 guinea pigs: cell-mediated immunity and IgG isoelectric focusing in myelin basic protein-liposome-treated and untreated animals

Juvenile strain-13 guinea pigs challenged with whole central nervous system (CNS) tissue in complete Freund's adjuvant (CFA) developed chronic-relapsing (CR) experimental allergic encephalomyelitis (EAE). The animals that recovered from the first clinical episode were divided into three groups. One group was left untreated, one group was treated with three intracardiac injections of 100 micrograms glutaraldehyde-fixed myelin basic protein (MBP)-liposomes (MBP-L-GA) given once a week, and one group was treated with cytochrome c-liposomes (CYC-L-GA). The animals treated with MBP-liposomes were very well protected against further relapses. In vitro proliferative responses of peripheral blood lymphocytes (PBL) were performed repeatedly on most animals. The lymphocytes exhibited excellent proliferative responses to MBP, proteolipid apoprotein (PLP) and whole myelin, as well as to purified protein derivative (PPD) and concanavalin-A (ConA). High proliferative responses were recorded over the entire period of observation which lasted 12-22 months, each time the animals were tested in remission or in full relapse. However, a sharp decrease in proliferative responses was observed in most animals when the assay was performed 24-48 h before to 24 h after entering a relapse. The results demonstrate the presence of long-term and sustained cell-mediated responses to two distinct neuroantigens, and show fluctuations of both neuroantigen-specific and nonspecific responses concordant with a well-defined phase of the disease. Isoelectric focusing and immunofixation was performed on sera and cerebrospinal fluids obtained at the time of sacrifice. The pattern showed clear oligoclonal IgG bands (OB) in the samples obtained from untreated, CYC-L-GA-treated as well as in the MBP-L-GA-treated animals.

Characterization of a major encephalitogenic T cell epitope in SJL/J mice with synthetic oligopeptides of myelin basic protein

The C-terminal 89-169 amino acid fragment of myelin basic protein (MBP) causes experimental allergic encephalomyelitis (EAE) in SJL/J mice. In order to identify the encephalitogenic T cell epitope, we have examined the fine specificity of encephalitogenic SJL/J T cell clones with synthetic peptides derived from the C-terminal 89-169 amino acids of MBP. These peptides were examined for their immunogenic and encephalitogenic activity in the SJL/J mouse. The SJL/J-derived, encephalitogenic T cell clone, 4b.14a, was shown to be responsive to rat myelin basic protein synthetic peptides pR89-101 (VHFFKNIVTPRTP) as well as to intact MBP. Its response was effectively blocked by mAb 10-2.16 (anti-I-As) as was the response to intact MBP. Furthermore, pR89-101 was revealed to be highly immunogenic for the (PLSJ)F1 mouse in terms of lymphocyte proliferation, but not for the PL/J mouse, in spite of the fact that there exists a strong bias to H-2u restricted responses in the (PLSJ)F1 mouse at the T cell level. By using pR89-101, T cells of (PLSJ)F1 origin were revealed to recognize the peptide in association with the I-As molecule on (PLSJ)F1 antigen presenting cells (APC). When examined for encephalitogenicity for the SJL/J mouse, pR89-101 was found to be as encephalitogenic as intact rat MBP. These results demonstrated that MBP peptide pR89-101 is a major encephalitogenic determinant for the SJL/J mouse.

Experimental allergic encephalomyelitis: the balance between encephalitogenic T lymphocytes and demyelinating antibodies determines size and structure of demyelinated lesions

The effect of a circulating monoclonal antibody recognizing an antigen located on the surface of myelin sheaths (myelin/oligodendroglia glycoprotein, MOG) on clinical and histopathological expression of experimental allergic encephalomyelitis (EAE) was tested in a model of EAE passively transferred by monospecific T lymphocytes. Intravenous injection of anti-MOG antibody at the onset of the disease massively augmented clinical impairment as well as primary demyelination. The structure of the CNS lesions depended on the balance between encephalitogenic T cells and anti-MOG antibody: when EAE was induced with high numbers of T cells, circulating anti-MOG antibody resulted in ubiquitous perivenous demyelination in the spinal cord and medulla oblongata. On the contrary, focal confluent demyelinated lesions were observed in animals injected with low numbers of T cells (even as few as 10(4] and anti-MOG antibody. Our studies, thus, indicate that the formation of inflammatory demyelinating lesions may be due to a synergistic action of cellular and humoral immune mechanisms.

Myelin proteolipid protein induces demyelinating disease in mice

Using two methods of immunization (A and B), 5/10 (A) and 27/45 (B), BALB/c by J mice immunized with human myelin proteolipid protein developed a demyelinating disease with a spectrum of chronic progressive to relapsing-remitting courses. Demyelinative lesions were seen histopathologically in all clinically affected animals that were examined. Many of the clinically unaffected animals also had histopathologic evidence of demyelination. Some of the animals had evidence of multiple ages of foci of activity. Evidence is presented that contamination with myelin basic protein could not account for the disease. This is a new model for multiple sclerosis in mice.

The detection of brain antigens within the circulating immune complexes of patients with multiple sclerosis

Immune complexes isolated from sera of patients with multiple sclerosis (MS) were analyzed for their antigenic content. Immune complexes precipitated with polyethylene glycol were inoculated into rabbits. The antisera raised were shown to react to MS and normal brain antigens by crossed immunoelectrophoresis, ELISA and nitrocellulose transfer. Additionally, these antisera reacted by co-precipitation with the measles nucleocapsid antigen. As persistent viral infection has not been shown to occur in MS, these studies support the possibility that brain antigens within the immune complex share antigenic determinants with a specific viral antigen seen earlier in life by the host.

The role of charge microheterogeneity of basic protein in the formation and maintenance of the multilayered structure of myelin: a possible role in multiple sclerosis

Isolation of several of the charge isomers from both normal and multiple sclerosis (MS) myelin basic protein (MBP) was achieved on CM-52 columns at pH 10.6. In liquid x-ray diffraction and aggregation experiments, corresponding charge isomers were equally effective in the formation of multilayers, demonstrating the dominant role of overall net positive charge. These studies demonstrated that the change in overall charge of MBP of one net positive charge was sufficient to produce large changes in aggregation and in multilayer formation. The x-ray diffraction experiments showed that component 1 was twice as effective as component 2 although they differed in charge by a single positive charge. Component 3 was less effective than component 2 and component "8" was not effective at all. Vesicle aggregation also showed a dependence on net positive charge. In order of decreasing effectiveness, component 1 greater than component 2 greater than component 3 greater than component "8". Since overall charge on MBP is determined by contributions from the various charge isomers, the relative proportions of these charge isomers favoring the less cationic components could explain the observation that MBP from MS victims was less effective than MBP from normal brain in vesicle aggregation and multilayer formation. The isolation of myelin-containing white matter fractions from both normal and MS tissue in which the loss of some of the most cationic charge isomers was correlated with presence of less compact myelin supports this hypothesis.

Chronic experimental allergic encephalomyelitis in guinea pigs induced by proteolipid protein

A chronic experimental allergic encephalomyelitis (EAE) was produced in Hartley guinea pigs with bovine white matter proteolipid protein (PLP), in which the levels of myelin basic protein (MBP) and galactocerebroside (GC) were less than 0.014% and 0.13%, respectively, by our method of purification. Cells of an MBP-specific T-cell line did not proliferate in the presence of 100 micrograms of PLP and antigen-presenting cells. Eleven animals were sensitized with 250 micrograms of PLP in Freund's complete adjuvant. Three guinea pigs developed paraplegia about 45 days after sensitization. Histological examination of the three animals revealed marked demyelinating lesions in the spinal cord, particularly in the dorsal columns and subpial regions of the lateral and anterior columns. Another guinea pig without apparent clinical symptoms had demyelinating plaques in the dorsal columns of the spinal cord and periventricular white matter of the brain. Antibodies to PLP were highly elevated in the animals with demyelinating plaques but antibodies to MBP and GC were not elevated in the serum samples. Skin response to PLP was positive in sensitized animals, but was not related to the clinical state. Since none of four strain 13 guinea pigs developed chronic EAE, it seems to be strain specific. These results suggest that PLP is encephalitogenic and produces demyelination in the central nervous system without contamination by MBP or GC in Hartley guinea pigs.

Deacylation of myelin proteolipid protein in organic solvents

A procedure has been developed for the deacylation of the hydrophobic, myelin proteolipid apoprotein using hydroxylamine in an alkaline organic solvent medium. Complete removal of covalently bound fatty acids was obtained after 4 hr of treatment. After deacylation, no changes could be detected in the electrophoretic pattern or in the number of free sulfhydryl groups. The deacylated apoprotein remains soluble in chloroform-methanol mixtures and is suitable for further physicochemical characterization.

The role of myelin lipids in experimental allergic encephalomyelitis. Part 1. Influence on disease production by non-encephalitogenic doses of myelin basic protein

Hartley guinea pig central nervous system (CNS) myelin has been purified and fractionated into its protein and lipid components. Experimental allergic encephalomyelitis (EAE) was induced in juvenile strain 13 guinea pigs with both lyophilized and fresh 'wet' myelin. However, a larger dose of lyophilized myelin was required to induce chronic EAE. Total myelin lipids, galactocerebrosides, gangliosides, phospholipids or proteolipids were combined with a non-encephalitogenic dose of myelin basic protein (MBP) and injected in juvenile Hartley guinea pigs. No clinical or histological manifestations of disease were observed. Parameters of immune functions indicated that the total myelin lipids augmented cell-mediated immune responses as measured by in vitro lymphocyte transformation and by a significant decrease in the percentage of peripheral early T cells. Only the proteolipids elicited delayed hypersensitivity reactions. Animals that received the phospholipid-MBP combination showed no changes when compared to animals injected with MBP alone. The results suggest that although the myelin lipids did not act synergistically with a non-encephalitogenic dose of MBP to induce EAE, they induced immunological changes and potentiated the immune response to MBP.

Delayed-type hypersensitivity to myelin basic proteins in mice susceptible to allergic encephalomyelitis

The delayed-type hypersensitivity (DTH) response in mice immunized with autologous spinal cord homogenate or purified myelin basic protein (MBP) was measured by the 125I-UdR uptake ear assay. Mice were tested for DTH responses with MBP preparations from different species and with synthetic peptides. The 114-122 and 68-84 peptide regions appear to be major determinants for inducing and eliciting DTH in the mice which are susceptible to allergic encephalomyelitis.

Interaction between human myelin basic protein and lipophilin

The interaction of human myelin basic protein with lipophilin has been demonstrated by affinity chromatography. The interaction was specific since neither basic protein, nor albumin bound to an affinity column consisting of BP bound to agarose. Conversely an albumin affinity column failed to bind BP. The pH dependency of the interaction correlated with the known pK for histidine. By the use of large peptides formed by tryptophanyl cleavage by BNPS-skatole, peptide 1-117 bound to the BP affinity column while neither the smaller peptide, 118-170, nor the synthetic nonapeptide bound. The large fragment contains 9 of the 10 histidines in the molecule which may explain the binding of this fragment. The result of such protein-protein interactions makes available a large number of new antigenic sites and extends considerably the range of encephalitogens for disease induction.

X-ray scattering studies of a model complex of lipid and basic protein of myelin

Low-angle and wide-angle X-ray scattering data from phosphatidylglycerol complexed with myelin basic protein, poly(L-lysine) and calcium ions are analyzed. The results confirm our earlier report (Brady, G.W., Murthy, N.S., Fein, D.B., Wood, D.D. and Moscarello, M.A. (1981) Biophys. J. 34, 345-350) that the basic protein interacts primarily with the polar headgroups of the lipid; and that at high protein concentrations (greater than 35%) the bilayers aggregate to form multilayers with a repeat period of 68 A, the single bilayer to multilayer transition being a cooperative process. Polylysine and Ca2+ produce multilayers with a smaller repeat of approx. 55 A. Basic protein and polylysine do not change the fluid-like arrangement of the hydrocarbon chains (diffuse 4.6 A peak in the wide-angle pattern), whereas Ca2+ probably induces a two-dimensional order (4.3 A and 3.9 A peak in the wide-angle pattern). Electron density profiles of the lipid and lipid-basic protein vesicles indicate that the basic protein penetrates into the bilayer.

Etiology and pathogenesis of monophasic and relapsing inflammatory demyelination - human and experimental

The close similarity of the CNS lesions in cr-EAE and MS renders this model especially valuable for the study of pathogenetic factors, leading to the formation of inflammatory demyelinated plaques. Recent evidence indicates, that various immune reactions, directed against different CNS antigens cooperate in the formation of the plaques. Furthermore it is discussed, that a combination of virus infection and autoimmunity may result in similarity structured lesions. It is thus propose that multiple different etiologic factors (autoimmune as well as exogenous events) may lead to the clinical pathohistological syndrome of multiple sclerosis.

Lipophilin-induced experimental allergic encephalomyelitis in guinea pigs

Clinical signs of EAE were infrequently observed (1/20) in adult Hartley guinea pigs challenged with isolated human myelin lipophilin in complete Freund's adjuvant. However, CNS vasculitis and parenchymal infiltration by inflammatory cells were found in 10 of 20 inoculated animals. Localized, nonconfluent, small demyelinated lesions were detected in the brain and spinal cord of 5/20 Hartley guinea pigs during an observation period of 120 days. The frequency of both inflammatory and demyelinated lesions in Hartley animals appeared to be dose-dependent, but extensive demyelinated lesions were not induced. Persistent residual inoculation mixture at the site of injection was found in animals showing CNS inflammatory and/or demyelinated lesions. In contrast to the Hartley strain, young strain 13 guinea pigs were clinically and pathologically unresponsive to challenge with lipophilin and mycobacteria in water-in-oil emulsion.