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Biomedical subjects

C Linington

Publications and source records attributed to C Linington.

At least 73 records · Page 4Linked to original sources
PubMed1992

Myelin/oligodendrocyte glycoprotein is a unique member of the immunoglobulin superfamily.

Myelin/oligodendrocyte glycoprotein (MOG) is a primary target autoantigen in experimental autoimmune encephalomyelitis, a widely used animal model for autoimmune demyelinating diseases such as multiple sclerosis. We have isolated several rat MOG cDNAs and confirmed their identity by comparison with MOG N-terminal peptide sequence. As expected, MOG mRNA expression is CNS-specific and peaks during active myelination. Our studies show that full length MOG mRNA is approximately 1.6 kb and encodes a signal peptide of 27 amino acids, followed by 218 residues for mature MOG (24,962 MW). A single site for N-glycosylation is found at Asn-31. Rather than the ubiquitous AAUAAA polyadenylation signal, a series of three overlapping, rare poly A signals were identified. The N-terminal half of mature MOG shares 52% identity with bovine butyrophilin, a possible lipid receptor. This same region has 39% identity with chicken B-G antigen, a major histocompatibility complex antigen involved in B cell selection and immune repertoire development. We show that both MOG and butyrophilin, each exhibiting a single Ig-like variable region domain, meet criteria for inclusion in the immunoglobulin superfamily. Moreover, MOG appears to represent a unique member of this superfamily in that it possesses two potential transmembrane domains, in contrast to a single membrane-spanning domain or glycophospholipid anchor found in all other members of Ig superfamily members.

Animals↗
PubMed1992

Molecular mimicry and the autoimmune response to the peripheral nerve myelin P0 glycoprotein.

In the Lewis rat immunisation with the myelin P0 glycoprotein can induce an inflammatory demyelinating disease of the peripheral nervous system, experimental allergic neuritis (EAN), which has many clinical and histopathological parallels with the human disease the Guillain-Barre syndrome. In view of the reported association of GBS with a number of infectious agents we have investigated whether "molecular mimicry" may occur between microbial antigens and the P0 protein that could possibly trigger a similar pathogenic autoimmune response in man. A computer search of the available protein sequence data bases identified several absolute sequence homologies between P0 and viral proteins that involve five or more consecutive amino acid residues. Four of these sequence homologies involved viral pathogens previously associated with the Guillain-Barre syndrome, namely Epstein-Barr virus (EBV), cytomegalovirus (CMV), Varicella zoster virus (VZV) and human immunodeficiency virus I (HIV I). Although, sequence homologies were also found between viral peptides and the neuritogenic determinants of P0, residues 56-71 and 180-199, these homologies proved incapable of eliciting EAN in the Lewis rat. These observations are discussed with reference to the role that molecular mimicry between T cell epitopes on pathogen derived antigens and the P0 protein may play in the pathogenesis of the Guillain-Barre syndrome.

Amino Acid Sequence↗
PubMed1992

T cell responses to myelin proteins in Guillain-Barré syndrome.

We have investigated the hypothesis that the pathogenesis of Guillain-Barré syndrome (GBS) involves an autoimmune T cell response to P0 and P2 proteins of peripheral nerve myelin. The proliferative responses of blood mononuclear cells (MNC) to myelin proteins and synthetic peptides derived from them were determined in patients with GBS and chronic idiopathic demyelinating polyradiculoneuropathy (CIDP), normal controls (NC) and patients with other neuropathies (ONP). Twelve out of 19 GBS patients responded to P0 or P2, 6 to P0 and its peptides only, 3 to P2 and its peptides only, and 3 to both P0 and P2 antigens. Responses to at least one of the antigens were also found in 6/13 of CIDP patients, but in only 4/17 NC and 2/6 ONP. Immune responses in GBS are heterogeneous. The early T cell responses to P0 protein, described here for the first time, may be important in the pathogenesis of some cases.

Adult↗
PubMed1992

Induction of persistently demyelinated lesions in the rat following the repeated adoptive transfer of encephalitogenic T cells and demyelinating antibody.

A chronic relapsing model of demyelinating experimental allergic encephalomyelitis (EAE) was induced in Lewis rats by the repeated co-transfer of encephalitogenic, myelin basic protein (MBP)-specific T cells in combination with a demyelinating monoclonal antibody (mAb) specific for the myelin oligodendrocyte glycoprotein (MOG). In controls, repeated injections of 5 x 10(5) MBP-specific T cells at intervals of 18-21 days resulted in an increasing resistance to the induction of further episodes of EAE. However, intravenous injection of the mAb 4 days after each T cell transfer overcame this 'vaccination' effect and induced severe clinical relapses associated with an increasing and persistent neurological deficit. Histological examination revealed that four cycles of treatment with T cells and mAb were sufficient to result in the formation of large plaques of demyelination in the spinal cord that failed to undergo significant remyelination within 60 days of the final injection of mAb. These lesions consisted of a matrix of astrocytic scar tissue traversed by numerous naked axons. These observations demonstrate that the formation of large, persistently, demyelinated lesions in a T cell-mediated model of EAE in the Lewis rat is dependent on the presence of an appropriate anti-myelin autoantibody response.

Animals↗
PubMed1992

Spinal cord microglia in experimental allergic neuritis. Evidence for fast and remote activation.

We have studied the response and the spatial distribution pattern of microglial cells during experimental allergic neuritis induced in the Lewis rat by the transfer of varying doses of activated T cells specific either for the P2 or P0 protein. The microglial reaction was studied immunocytochemically at the light and electron microscopic level using a panel of monoclonal antibodies which included two recently produced antibodies against rat microglial cells, Murine Clone 101 and 102. Activation of microglial cells became apparent through changes in their immunophenotype and morphology within 48 hours of T cell transfer and therefore preceded the onset of clinical disease. Activated microglial cells showed an increased expression of the complement type three receptor, the murine clone 101 and 102 determinants and major histocompatibility complex antigens. The microglial reaction in experimental allergic neuritis occurs at a site remote from the inflammatory changes in the peripheral nerve, the microglial reaction being most prominent in the dorsal and ventral grey matter of the lumbar and the thoracic spinal cord. Similar changes were also observed at this time in the terminal projection fields of the primary, afferent, sensory fibers, such as the nucleus gracilis. Subsequently, after 7 days, motoneurons, particularly in the ventral grey matter of the lumbar spinal cord, were ensheathed by perineuronal microglial cells. These perineuronal microglial cells were in close contact with the neuronal plasma membrane and occasionally appeared to detach afferent synaptic terminals from the surface. Microglial responses were not detected in animals injected with nonpathogenic T cells specific either for the purified protein derivative or ovalbumin. This early activation of microglial cells observed in experimental allergic neuritis suggests that a rapid and remote signaling might be operating in the microglial responses during T cell-mediated autoimmune diseases.

Animals↗
PubMed1991

T and B cell responses to myelin-oligodendrocyte glycoprotein in multiple sclerosis.

The pathogenesis of multiple sclerosis (MS) is believed to involve an autoimmune component directed against the myelin sheath. One potential target Ag for such autoimmune attack is the myelin-oligodendrocyte glycoprotein (MOG) because an anti-MOG mAb has profound influence on the course of experimental autoimmune encephalomyelitis, which to some extent represents an experimental model of MS. Using single cell assays, we have evaluated T and B cell reactivities to MOG in MS patients and controls. T cell reactivity was estimated by counting the number of cells that secreted IFN-gamma in response to MOG, whereas B cell reactivity was estimated by enumerating cells secreting antibodies that bound to MOG. MOG reactive T cells were detected in the peripheral blood of the majority of the 16 MS patients examined (mean 1/7299 mononuclear cells), but infrequently and at lower numbers in samples from neurologic controls. MOG-reactive T cells were more frequent among MS patients' cerebrospinal fluid (CSF) mononuclear cells (mean 1/450 cells). The T cell response to MOG was evidently MHC class II restricted, because Fab fragments of a rabbit polyclonal anti HLA-DR antibodies abrogated the Ag-induced increase in number of cells that secreted IFN-gamma, as analyzed on CSF and PBMC from three patients with MS. Anti-MOG IgG antibody-secreting cells were detected in blood in 8 of 16 MS patients (mean 1/25,641 cells), but they were also strongly accumulated in CSF, being detected in 8 of 10 MS patients examined (mean 1/265 cells), while rarely found in controls. The findings imply that MOG may represent a pathogenetically important target Ag in MS.

Adult↗
PubMed1991

Antibodies to myelin-oligodendrocyte glycoprotein in cerebrospinal fluid from patients with multiple sclerosis and controls.

Myelin-oligodendrocyte glycoprotein (MOG) has been implicated as a target for antibody-mediated immune attack in experimental autoimmune encephalomyelitis (EAE) which has been used extensively as an experimental model of multiple sclerosis (MS). We have screened cerebrospinal fluid (CSF) and plasma from 30 patients with MS, 30 with other neurological diseases (OND) and 30 with tension headache for anti-MOG antibodies of IgG isotype by enzyme-linked immunosorbent assay (ELISA). Such antibodies were detected in CSF from seven of the patients with MS, compared to two with OND and one with tension headache. No anti-MOG IgG antibodies were demonstrable in plasma. Antibody specificity was confirmed by Western blot immunostaining. Antibody levels were higher in MS compared to OND and tension headache. No correlation was observed between anti-MOG IgG antibodies and total IgG levels in CSF. The significance of anti-MOG antibodies demonstrated in MS CSF remains to be defined.

Adult↗
PubMed1991

Antibody-mediated demyelination in experimental allergic encephalomyelitis is independent of complement membrane attack complex formation.

The effects of decomplementation by cobra venom factor (CVF) on the pathogenesis of inflammation and demyelination in experimental allergic encephalomyelitis (EAE) and acute antibody-mediated demyelinating EAE (ADEAE) have been quantified histologically and immunocytochemically. In rats immunized with 50 micrograms of myelin basic protein in Freund's complete adjuvant containing 100 micrograms heat-killed Mycobacterium tuberculosis H37Ra, clinical signs of EAE were completely suppressed by two injections of CVF given 9 and 12 days post-immunization. Suppression of clinical disease was associated with a dramatic reduction in peri-vascular inflammation in the CNS, although immunohistochemical staining identified small numbers of infiltrating T cells and macrophages. In contrast, CVF treatment had no significant effect on the clinical severity of ADEAE and although C9 deposition within the CNS was virtually abolished, there was no statistically significant decrease in the extent of demyelination or inflammation. These observations indicate that in the absence of complement components C3 and C5 an antibody-dependent cell-mediated cytotoxic response plays an important role in the pathogenesis of antibody-mediated demyelination. The major role of the complement cascade in EAE appears to be the generation of pro-inflammatory factors that enhance the inflammatory response within the CNS in animals facing a mild encephalitogenic challenge.

Animals↗
PubMed1990

The immune response to myelin proteolipid protein in the Lewis rat: identification of the immunodominant B cell epitope.

The polyclonal antibody response of the Lewis rat to bovine myelin proteolipid protein (PLP) has been investigated following immunisation with either the purified protein or bovine central nervous system myelin. In both situations, the carboxyl-terminal sequence of PLP was identified as the immunodominant domain of this protein and epitope mapping demonstrated that the carboxyl-terminal amino acid, phenylalanine276, was a critical requirement for antibody recognition of this epitope. This single epitope accounted for approximately 78% and 56% of the antibody response to PLP in rats immunised with PLP or bovine myelin, respectively. Polyclonal rat antibodies specific for this carboxyl terminal epitope of PLP were also obtained following immunisation with a synthetic 20 amino acid oligopeptide analogue of the carboxyl-terminal sequence of PLP. Western blotting demonstrated this antibody response was specific for the PLP and DM-20 components of mammalian central nervous system myelin. In contrast, no major PLP epitopes were detected within the PLP amino acid sequences 35-58 and 91-150, the other major hydrophilic domains of this protein.

Amino Acid Sequence↗
PubMed1990

Identification of an encephalitogenic determinant of myelin proteolipid protein for the rabbit.

A late onset, demyelinating form of experimental allergic encephalomyelitis (EAE) was induced in New Zealand White rabbits following immunisation with a synthetic peptide representing the amino acid sequence 91-110 of bovine myelin proteolipid protein (PLP). Histologically, disease was associated with varying degrees of central nervous system (CNS) inflammation, which in six of seven animals was accompanied by axonal degeneration and secondary demyelination. Primary demyelination with axonal sparing was generally absent in this model of EAE. Immunohistochemical and immunoelectron microscopic analysis of CNS tissue indicate that B cell epitopes within this encephalitogenic PLP sequence are not exposed at the surface of the myelin sheath, but are sequestered within compact multilamellar myelin. Furthermore, no correlation was observed between the anti-PLP antibody titer induced by the peptide and either the clinical severity or histopathology of the disease. These observations suggest that the B cell response to epitopes within the PLP sequence 91-110 does not play a primary role in the immunopathogenesis of PLP-induced EAE.

Animals↗
PubMed1990

Conservation of the carboxyl terminal epitope of myelin proteolipid protein in the tetrapods and lobe-finned fish.

Immunochemical analysis of the myelin proteolipid protein (PLP) has identified the carboxyl terminal amino acid phenylalanine 276 as the only PLP epitope conserved between the PLP components of rat and lungfish, species representing the phylogenetically most widely separated groups that synthesise typical CNS myelin. Immunoblotting using a rabbit antiserum raised against the carboxyl terminal sequence of rat PLP (residues 257-276) identified this epitope on the PLP components of both tetrapod (rat, chicken, lizard, and frog) and lobe-finned fish (coelacanth and lungfish) CNS myelin, including the DM-20 isoform of PLP, which is restricted to rat, chicken, and lizard CNS myelin. The conservation of the carboxyl terminus of PLP during evolution suggests this structure may play an important role in maintaining the organisation and function of PLP in the myelin membrane.

Animals↗
PubMed1989

Vesicular removal by oligodendrocytes of membrane attack complexes formed by activated complement.

Oligodendrocytes synthesize myelin in the central nervous system and maintain it in lamellar sheaths around axons. Techniques for studying oligodendrocyte development in vitro can be used, indirectly, to investigate the myelin injury that occurs in human and experimental demyelinating disease. Cell-mediated immune mechanisms are necessary but not sufficient to induce myelin damage in vivo; more recently complement has also been implicated in the pathogenesis both of multiple sclerosis and experimental allergic encephalomyelitis. Previously we have demonstrated that antibody-independent complement activation occurs in vitro at the oligodendrocyte surface. Here we show that the ensuing oligodendrocyte injury is reversible, and that recovery involves the release of membrane-attack complex-enriched vesicles from the surface of viable cells. The demonstration of morphologically and immunochemically identical vesicles in the cerebrospinal fluid of patients with multiple sclerosis suggests that reversible complement-mediated injury contributes to myelin damage in vivo.

Animals↗
PubMed1989

Immunohistochemical localisation of terminal complement component C9 in experimental allergic encephalomyelitis.

The deposition of terminal complement component C9 within the central nervous system (CNS) has been studied immunohistochemically in three models of experimental allergic encephalomyelitis (EAE) in the rat; inflammatory EAE induced by the passive transfer of myelin basic protein-specific T cells (tEAE), antibody-mediated, demyelinating tEAE and a subacute/chronic model induced by active immunisation with guinea pig spinal cord tissue in adjuvant. Two distinct patterns of C9 reactivity were observed, a diffuse staining of the tissue adjacent to inflammatory lesions, similar to that seen for other extra-vasculated serum proteins, and also granular, sometimes fibrillar C9 deposits around some inflammed vessels and in areas of active demyelination. The latter staining pattern was most pronounced in animals with acute antibody-mediated demyelinating tEAE, in which extensive, but transient, subpial and perivascular granular deposits of C9 were associated with regions of acute demyelination. A similar pattern of granular C9 reactivity was also associated with demyelinating lesions in animals with actively induced chronic progressive EAE. However, these C9 deposits were not observed in rats with purely inflammatory, clinically mild tEAE, although C9 deposition was occasionally observed around a small number of inflammed vessels in animals with hyperacute, lethal tEAE. These observations demonstrate that deposition of C9, the major component of the cytolytic membrane attack complex, in EAE is related to myelin injury rather than CNS inflammation.

Animals↗
PubMed1989

Normal rat serum cytotoxicity against syngeneic oligodendrocytes. Complement activation and attack in the absence of anti-myelin antibodies.

The role of complement in mediating oligodendrocyte and myelin injury has been investigated by studying the effects of normal adult rat serum on syngeneic cultured neonatal glial cells. Rat serum has cytotoxic activity directed against oligodendrocytes but not astrocytes, the potency of which increases with cell maturation. The effects of heat inactivation, decomplemented rat serum, EGTA treatment, removal of any possible anti-myelin antibody by absorption using syngeneic myelin and absence of surface staining for immunoglobulins on serum-treated oligodendrocytes, C9 depletion and reconstitution, and oligodendrocyte staining for surface C9 demonstrate that this cytotoxicity is mediated by complement via antibody independent activation of the classical pathway and is membrane attack complex dependent. These findings significantly extend the previous demonstration of complement activation by extracted myelin, and may have significance for the pathogenesis of demyelinating diseases.

Animals↗
PubMed1989

Myelin-oligodendrocyte glycoprotein (MOG) is a surface marker of oligodendrocyte maturation.

The myelin-oligodendrocyte glycoprotein (MOG) is a minor component of central nervous system myelin. Using neonatal rat optic nerve oligodendrocyte cultures we have compared the development in vitro of MOG with galactocerebroside, myelin basic protein and 2' ,3'-cyclic-nucleotide 3'-phosphodiesterase. MOG appears on the surface of oligodendrocytes 1-2 days later than these other oligodendrocyte markers, suggesting that MOG may be a useful indicator of oligodendrocyte maturation. The relevance of these findings for investigating mechanisms of myelin injury in vitro and the role of oligodendrocyte damage in demyelinating disease is discussed.

Animals↗
PubMed1989

Identification of a common idiotype on myelin oligodendrocyte glycoprotein-specific autoantibodies in chronic relapsing experimental allergic encephalomyelitis.

The myelin/oligodendrocyte glycoprotein (MOG) is a target antigen for autoantibody-mediated demyelination in chronic relapsing experimental allergic encephalomyelitis (CREAE) in the Strain 13 guinea pig. Anti-idiotypic antibodies directed against a demyelinating MOG-specific monoclonal antibody (8-18C5) have identified a cross-reactive idiotype in 10/10 CREAE sera. In nine of these sera inhibition studies demonstrated that this idiotype was at or in close proximity to the combination site of guinea pig anti-MOG autoantibodies. This cross-reactive anti-MOG idiotype may represent an important target for the anti-idiotypic regulation of demyelinating antibody responses in CREAE.

Animals↗
PubMed1989

The role of complement in the pathogenesis of experimental allergic encephalomyelitis.

The role of complement in the pathogenesis of demyelination and inflammation has been investigated in a synergistic model of acute experimental allergic encephalomyelitis (EAE) in the Lewis rat. Depletion of serum complement with cobra venom factor (CVF) suppressed the clinical expression of acute inflammatory EAE induced either by immunization with 50 micrograms guinea pig basic protein (MBP) in Freund's complete adjuvant, or by the passive transfer of 10(7), but not 5 X 10(7) MBP activated spleen cells. Despite the suppression of clinical disease in actively induced EAE, treatment with CFF only had a significant effect on the severity of CNS inflammation in early disease (12 days postimmunization) when the number of inflammatory foci was reduced by 35%. Three days later this difference had resolved and no significant difference could be detected in the severity of CNS inflammation, although control animals exhibited severe disease, the CVF treated group being clinically normal. Demyelination in these models is initiated by systemic injection of the antimyelin oligodendrocyte glycoprotein (MOG) monoclonal antibody, 8-18C5, which in vitro lyses oligodendrocytes in a dose, Fc and complement-dependent manner and in vivo induces extensive CNS demyelination in rats with EAE. Treatment with CVF reduced the ability of this antibody to initiate demyelination in vivo and furthermore, its F(ab)2' fragment had no effect on the clinical course of EAE and was unable to initiate demyelination in normal animals. Complement-dependent mechanisms are therefore involved both in the clinical expression of acute inflammatory lesions and in the pathogenesis of antibody-mediated demyelination in EAE.

Animals↗