Molecular characteristics of the epitope in myelin-associated glycoprotein that is recognized by a monoclonal IgM in human neuropathy patients

Mécanismes cellulaires et moléculaires de la croissance axonale

INTRODUCTION

During embryonic and post-natal development, numerous axonal connections are formed establishing a functional nervous system. Knowledge of the underlying molecular and cellular mechanisms controlling this phenomenon is improving.

STATE OF THE ART

In this review, we present the general principles of axon guidance together with the major families of guidance signals. This includes the tyrosine kinase receptors Eph and their ligands Ephrins, the netrins, the semaphorins, the slits and other major components of the extracellular matrix. These types of guidance signals share common functional properties leading to actin cytoskeleton remodelling. The direct or indirect interactions between the receptors of these guidance cues and actin modulators is the final step of the signalling cascade constituting the fundamental mechanism defining the orientation and extension of the axonal growth cone. These factors are involved in the formation of many, if not all, axonal projections for which they act as repulsive (inhibitory) or attractive (promoting) signals.

PERSPECTIVES

the knowledge of these mechanisms is particularly interesting since the inhibition of axonal outgrowth is considered to be one of the major obstacles to nerve regeneration in the central nervous system. Indeed, most of the guidance signals expressed during brain development are up-regulated in lesion sites where they contribute to the lack of nerve re-growth. Here, we present the nature of the mechanical barrier, the so called glial scar, and we describe the major inhibitory molecules preventing axonal extension.

CONCLUSION

the comprehension of the molecular mechanisms involved in axon growth and guidance represents a major advance towards the definition of novel therapeutic strategies improving nerve regeneration. The path to the clinical application of these molecular factors remains long. Nevertheless, the next decade will undoubtedly provide challenging data that will modify the current therapeutic approaches.

IgM M-protein in a patient with sensory-dominant neuropathy binds preferentially to polysialogangliosides

A 77-year-old man presented sensory-dominant neuropathy associated with IgM M-protein reacting with various gangliosides. The M-protein bound to gangliosides with polysialosyl residue, such as GD1b, GD3, GT1b, GT3, GQ1b, and GQ1c. In addition, GD1a, GM3 and LM1, having a terminal monosialosyl epitope, were also recognized. Previously, Ilyas et al. described a similar case in which sensory symptoms were associated with IgM M-protein reacting with gangliosides containing a disialosyl group, such as GD3, GD1b, and GT1b, but not GM3 and GD1a. It is suggested that the reactivity of IgM M-protein with polysialogangliosides may be associated with the pathogenesis of sensory-dominant neuropathy.

IgG monoclonal proteins from patients with axonal peripheral neuropathies bind to different epitopes of the 68 kDa neurofilament protein

We describe three patients with a sensorimotor axonal polyneuropathy and an IgG M-protein that binds to a 68 kDa axonal protein identified as the low molecular weight neurofilament protein (NF-L). The immunological studies revealed that the M-proteins have different target epitopes: one is phosphorylated and the other two are nonphosphorylated. One of the nonphosphorylated epitopes is common to other intermediate filaments, such as desmin and vimentin.

Axonal neuropathy in a patient with monoclonal IgM kappa reactive with Schmidt-Lantermann incisures

We report a patient with a progressive, predominantly sensory neuropathy and a IgM kappa M-protein that binds to Schmidt-Lantermann incisures. A sural nerve biopsy showed primary axonal damage and IgM deposits at Schmidt-Lantermann incisures were seen by direct immunoperoxidase. Serum from the patient injected into rat sciatic nerve reacts with the incisures as with those in the patient's nerve. The IgM kappa M-protein reacts with chondroitin sulfate C and binds to a broad nerve protein band with a mobility of between 170 and 118 kDa. Peripheral neuropathy may be related to the M-protein, which had immunocytochemical reactivity not previously described for patients with polyneuropathy and IgM monoclonal gammopathy.

Anti-myelin-associated glycoprotein antibodies in patients with a monoclonal IgM gammopathy and polyneuropathy, and a simplified method for the preparation of glycolipid antigens

The two sulfated glucuronic acid containing glycolipids, sulfate-3-glucuronyl paragloboside (SGPG) and sulfate-3-glucuronyl lactosaminyl paragloboside (SGLPG), were prepared by ion exchange chromatography of lipid extracts from bovine cauda equina. Thin layer chromatography (TLC) immunostaining and an enzyme-linked immunosorbent assay (ELISA) were used to show that the SGPG/SGLPG fraction was free of crossreactive antigenic components such as gangliosides. The results obtained by ELISA demonstrate that sera of all patients were validated IgM monoclonal anti-myelin-associated glycoprotein (MAG) demyelinating neuropathy display high titer antibodies with high affinity type titration curves. These antibodies were absent from the sera of 16 patients with other neurological diseases and ten normal controls. ELISA with SGPG/SGLPG as an antigen appears to be a valuable and highly specific immunodiagnostic test for determining anti-MAG antibody titers in the sera of patients. The amount (approximately 0.4 mg) of SGPG/SGLPG partially purified from 10 g of fresh tissue is sufficient for the preparation of approximately 100 96-well plates for ELISA procedures.

Preliminary studies on sensitization of Lewis rats with sulfated glucuronyl paragloboside

A large number of patients with peripheral neuropathy and IgM paraproteinemia have IgM monoclonal antibodies which recognize a carbohydrate determinant shared by myelin-associated glycoprotein (MAG) and sulfated glucuronyl glycolipids (SGGLs). There is considerable evidence that these IgM monoclonal antibodies are responsible for demyelination in this disorder. To study the pathogenic role of SGGLs in this type of neuropathy, we sensitized Lewis rats with sulfated glucuronyl paragloboside (SGPG), a major SGGL. Fifty percent of the animals (8/16) developed neurological symptoms such as mild to moderate distal tail tone loss, with or without abnormal posture, along with development of anti-SGPG antibodies. These antibodies reacted with SGGLs, but not with rat MAG. Morphological studies showed: (1) axonal change in the lateral aspects of the dorsal columns in the spinal cord; and (2) damage to the endothelial cells in the spinal cord which suggested a breakdown of the blood-brain barrier. There was no obvious change in the peripheral nerve. Since no marked cellular infiltration was detected in these lesions, the clinicopathological findings observed could be induced by humoral mechanism, most likely anti-SGPG antibodies.

Axonal neuropathy with monoclonal IgG kappa that binds to a neurofilament protein

We report a 74-year-old woman with a slowly progressive sensory motor axonal neuropathy and a monoclonal IgG-kappa that bound to a 68-kd axonal protein identified as the low molecular weight neurofilament protein. The sera of control subjects and disease controls did not bind to neurofilament protein.

Variability in the structural requirements for binding of human monoclonal anti-myelin-associated glycoprotein immunoglobulin M antibodies and HNK-1 to sphingoglycolipid antigens

A high proportion of patients with neuropathy have immunoglobulin M (IgM) paraproteins that react with carbohydrate determinants on the myelin-associated glycoprotein (MAG) and two sphingoglycolipids, 3-sulfoglucuronyl paragloboside (SGPG) and 3-sulfoglucuronyl lactosaminyl paragloboside. In order to characterize the fine specificities of these human antibodies further, the binding of 10 anti-MAG paraproteins to several chemically modified derivatives of SGPG was compared with the binding to intact SGPG by both TLC-overlay and enzyme-linked immunosorbent assay. The following derivatives were tested: the desulfated lipid, glucuronyl paragloboside (GPG); the methyl ester of GPG (MeGPG); the methyl ester of SGPG, 3-sulfomethylglucuronyl paragloboside (SMeGPG); and 3-sulfoglucosyl paragloboside (SGlcPG) produced by reduction of the carboxyl group of the glucuronic acid with sodium borohydride. All 10 IgM paraproteins and the related mouse IgM antibody, HNK-1, reacted most strongly with intact SGPG, but variations in the reactivity with the derivatives revealed striking differences in the structural requirements for binding between the antibodies.(ABSTRACT TRUNCATED AT 250 WORDS)

Sulfated glucuronyl paragloboside in rat brain microvessels

In patients with neuropathy associated with paraproteinemia, there are monoclonal immunoglobulin M antibodies reacting with myelin-associated glycoprotein and sulfated glucuronyl glycolipids. There are indications that the monoclonal antibodies may be responsible for these neuropathies. However, the mechanism by which the antibodies gain access to the nervous tissue, which is separated by the blood-brain barrier or blood-nerve barrier, is still unknown. In this study, we examined the presence of the sulfated glucuronyl glycolipid antigens on brain endothelial cells. Microvessels were isolated from adult Lewis rat brain cortex. Sulfated glucuronyl paragloboside (SGPG) was detected in the acidic lipid fraction by a TLC immunostaining method. Immunofluorescence studies showed positive staining on the surface of microvessels. In addition, SGPG could be detected in the cultured endothelial cells of human umbilical vein. These findings suggest that the endothelial cells contain antigenic sites for interaction with the autoantibodies. This type of interaction may result in damages to the endothelial cell function and may be responsible for changes in the blood-brain barrier permeability and the ensuing penetration of large molecules, such as immunoglobulins, into the endoneurial space.

The epitope(s) recognized by HNK-1 antibody and IgM paraprotein in neuropathy is present on several N-linked oligosaccharide structures on human P0 and myelin-associated glycoprotein

The mouse monoclonal antibody HNK-1 and the human monoclonal IgM antibody present in patients with polyneuropathy both recognize carbohydrate epitope(s) on human myelin-associated glycoprotein and P0. In the present study, the oligosaccharide structures that bear the antibody epitope(s) were investigated. The extracellular derivative of myelin-associated glycoprotein (dMAG) was purified by immunoaffinity chromatography. P0 was electroeluted from gel slices. Western blot analysis of whole glycoproteins demonstrated that the epitopes for HNK-1 and the human monoclonal IgM antibody were different. The glycopeptides obtained by proteolysis of purified dMAG and P0 were separated and characterized by affinity chromatography on concanavalin A-Sepharose. Both dMAG and P0 displayed heterogeneity in their oligosaccharide structures, i.e., they both contained mainly tri- and tetraantennary oligosaccharides (approximately 80%), although biantennary (10%) and high-mannose and/or hybrid (10%) oligosaccharides were present. The human monoclonal IgM antibody epitope was present on all types of isolated oligosaccharide structures from either dMAG and P0. The HNK-1 epitope was present on all types of oligosaccharide structures of dMAG, whereas it was present only on tri- and tetraantennary structures of P0.

Complement-mediated demyelination in patients with IgM monoclonal gammopathy and polyneuropathy

We investigated the role of complement in the pathogenesis of the demyelinating polyneuropathy that occurs in some patients with IgM monoclonal gammopathy. Seven patients with chronic sensorimotor polyneuropathy and IgM monoclonal gammopathy were examined. In six patients, the monoclonal protein recognized an epitope shared by myelin-associated glycoprotein and two peripheral-nerve glycolipids, whereas in one patient, IgM bound to an unidentified myelin antigen. Direct and indirect immunofluorescence and immunoperoxidase assays showed colocalization along the myelin sheaths of peripheral-nerve fibers of monoclonal protein with complement components C1q, C3d, and C5. In addition, terminal-complement complex that was not associated with S protein was detected in myelin sheaths. It appeared that alterations in myelin geometry caused by the separation of myelin lamellae corresponded to sites at which terminal-complement complex was deposited. We conclude that demyelination in polyneuropathy associated with IgM monoclonal gammopathy may be mediated by complement.

Autoimmune mechanisms in peripheral neuropathies

In certain patients with demyelinating neuropathy and plasma cell dyscrasia, there are IgM monoclonal antibodies that recognize a carbohydrate epitope shared by myelin-associated glycoprotein (MAG) and at least two acidic glycolipids in the peripheral nervous system (PNS). The structures of the two acidic lipids have been elucidated as a new class of glycosphingolipids, termed sulfoglucuronyl glycolipids (SGGLs). SGGLs have been demonstrated to be present in myelin, axolemma, and other glia-related membranes in PNS of several animal species, as well as in human dorsal root ganglia and sympathetic ganglia. In rabbits sensitized with sulfoglucuronyl paragloboside (SGPG), a major SGGL in PNS, antibodies developed with reactivities toward SGPG and MAG. The animals also showed moderate weakness, a slowed nerve conduction velocity, and evidence of conduction block. Recently we also found SGPG in rat brain microvessels. This finding supports our hypothesis that autoantibodies may first interact with endothelial cell-bound antigens and that this might change the permeability of the blood-brain or blood-nerve barrier to permit the entry of these autoantibodies into the nervous system. Our data are consistent with the concept that an autoimmune response against the sulfoglucuronyl residue may participate in the pathogenesis of immune-mediated neuropathy.

Anti-myelin-associated glycoprotein IgM antibody titers in neuropathy associated with macroglobulinemia

Twenty-seven patients with neuropathy and IgM monoclonal gammopathy were tested for antigen specificity of the M-protein and for anti-myelin-associated glycoprotein (MAG) IgM levels by immunoblot. In 16 patients (59.2%) the M-protein reacted with MAG and with cross-reactive glycoconjugates. Anti-MAG IgM titers in these patients ranged between 1:12,800 and 1:100,000. A fainter IgM reactivity with MAG and related glycoconjugates was detected in 3 additional patients with neuropathy, but also in 8 of 24 patients with IgM M-protein without neuropathy (33.3%). This reactivity was not due to the M-protein and corresponded to antibody titers of 1:400 or less in all but 1 patient with a titer of 1:3,200. Low titers of anti-MAG IgM (1:200 or less) were also detected in 17 of 101 control patients without IgM M-proteins (16.8%), while 1 patient with neuropathy of unknown cause had anti-MAG IgMK titers of 1:25,600. In 1 patient with neuropathy and IgM M-protein that was not anti-MAG, the M-protein bound to other antigens in nerve, while in 6, other possible causes or mechanisms for the neuropathy were found. In this study, high titers of anti-MAG IgM antibodies were always associated with neuropathy. The presence of low levels of anti-MAG IgM in a significant proportion of controls suggests that monoclonal expansion of naturally occurring B-cell clones secreting anti-MAG IgM may be responsible for the high incidence of this antigen specificity of the M-protein.

Identification and characterization of gangliosides reacting with IgM paraproteins in three patients with neuropathy associated with biclonal gammopathy

IgM monoclonal antibodies from three patients with polyneuropathy associated with biclonal gammopathy reacted with monosialoganglioside GM1 on thin-layer chromatograms. An IgM paraprotein in one of the patients with a predominantly motor neuropathy also reacted strongly with the ganglioside GD1b and asialo-GM1. All three of these antigenic lipids have a Gal(beta 1-3)GalNAc moiety in common which would appear to be the antigenic determinant. However, this IgM also cross-reacted weakly with paragloboside which has an N-acetyllactosaminyl [Gal(beta 1-4)GlcNAc] terminal structure. The specificity of the other paraprotein in this patient is not known. The IgM paraproteins reacting with GM1 in both of the other patients exhibited different specificity because they did not react with GD1b and asialo-GM1, but reacted strongly with GM2 ganglioside. The data suggest that the epitope for both of these IgMs is in the GalNAc(beta 1-4)(NeuAc alpha 2-3)Gal(beta 1-4)Glc region of the gangliosides that is common to both GM2 and GM1. The second IgM paraproteins in both of these latter patients react with the myelin-associated glycoprotein (MAG) and two 3-sulfoglucuronyl glycolipids that share antigenic determinants with MAG.

NK cells in patients with peripheral neuropathy and IgM monoclonal protein reacting with the myelin-associated glycoprotein (MAG)

We studied Leu 7+ cell distribution and natural killer (NK) activity in the peripheral blood of six patients who had peripheral neuropathy and monoclonal IgM protein directed against myelin-associated glycoprotein (anti-MAG IgM). We did not find any difference between patients and control subjects (healthy or polyneuropathic, some with IgM monoclonal paraprotein but without anti-MAG activity). The presence of autologous sera did not interfere with these results. We noted an increase in Leu 11+ cell percentages after pre-incubation of the patient cells with autologous sera but the phenotypes of cells from control subjects did not change after incubation with autologous or patient sera.

An immunoglobulin M monoclonal antibody, recognizing a subset of acetylcholinesterase molecules from electric organs of Electrophorus and Torpedo, belongs to the HNK-1 anti-carbohydrate family

An immunoglobulin M (IgM) monoclonal antibody (mAb Elec-39), obtained against asymmetric acetylcholinesterase (AChE) from Electrophorus electric organs, also reacts with a fraction of globular AChE (amphiphilic G2 form) from Torpedo electric organs. This antibody does not react with asymmetric AChE from Torpedo electric organs or with the enzyme from other tissues of Electrophorus or Torpedo. The corresponding epitope is removed by endoglycosidase F, showing that it is a carbohydrate. The subsets of Torpedo G2 that react or do not react with Elec-39 (Elec-39+ and Elec-39-) differ in their electrophoretic mobility under nondenaturing conditions; the Elec-39+ component also binds the lectins from Pisum sativum and Lens culinaris. Whereas the Elec-39- component is present at the earliest developmental stages examined, an Elec-39+ component becomes distinguishable only around the 70-mm stage. Its proportion increases progressively, but later than the rapid accumulation of the total G2 form. In immunoblots, mAb Elec-39 recognizes a number of proteins other than AChE from various tissues of several species. The specificity of Elec-39 resembles that of a family of anti-carbohydrate antibodies that includes HNK-1, L2, NC-1, NSP-4, as well as IgMs that occur in human neuropathies. Although some human neuropathy IgMs that recognize the myelin-associated glycoprotein did not react with Elec-39+ AChE, mAbs HNK-1, NC-1, and NSP-4 showed the same selectivity as Elec-39 for Torpedo G2 AChE, but differed in the formation of immune complexes.

Comparative binding of murine and human monoclonal antibodies reacting with myelin-associated glycoprotein to myelin and human lymphocytes

Human monoclonal IgM antibodies present in the blood of some patients with peripheral neuropathy and murine hybrid IgM antibodies C5 and C6, raised against myelin-associated glycoprotein, and HNK-1, raised against the human T cell line HSB-2, all bind to the carbohydrate moiety of myelin-associated glycoprotein. The relative avidity of the monoclonal antibodies was HNK-1 greater than C5/C6 much greater than human IgM, as determined in a competitive binding radioimmunoassay. HNK-1 bound myelin equally well at incubation temperatures between 4 degrees C and 37 degrees C; the human antibodies bound significantly only at 4 degrees C; and C6 bound best at 4 degrees C, less strongly at 20 degrees C and did not bind at 37 degrees C. All of the antibodies bound to a band corresponding to myelin-associated glycoprotein on immunoblots of human CNS myelin proteins in addition to several other antigens. Flow cytometric studies revealed that the murine but not the human antibodies bind to peripheral blood lymphocytes. Taken together, these data suggest that the antibodies probably recognize the same epitope but bind with different avidity.

Antibodies to glycolipids in demyelinating diseases of the human peripheral nervous system

Antibodies to complex glycolipids occur in patients with a variety of diseases of the peripheral nervous system. Many patients with demyelinating neuropathy occurring in association with IgM paraproteinemia have a monoclonal antibody that reacts with a carbohydrate determinant shared between sulfate-3-glucuronyl paragloboside (SGPG), the myelin-associated glycoprotein and other glycoproteins of peripheral nerve. Other patients with neuropathy in association with IgM paraproteinemia have monoclonal antibodies reacting with carbohydrate determinants on various gangliosides. More than 80% of the IgM monoclonal antibodies from patients of this type that have been screened in our laboratory react with SGPG or ganglioside antigens. High levels of antibodies reacting with ganglioside antigens are also found in some patients with inflammatory neuropathies such as Guillain-Barré Syndrome and chronic relapsing inflammatory polyneuropathy. The pathogenetic significance of these antibodies reacting with acidic sphingoglycolipids remains to be established.

Secretions of anti-myelin-associated glycoprotein antibodies by B cells from patients with neuropathy and nonmalignant monoclonal gammopathy

Four patients with peripheral neuropathy and nonmalignant monoclonal gammopathy with anti-myelin-associated glycoprotein (MAG) antibodies were studied to determine whether secretion of anti-MAG IgM antibodies by B cells was autonomous, or whether the monoclonal B cells were responsive to T cells. Secretion of anti-MAG IgM by isolated B cells was stimulated by the addition of increasing numbers of pokeweed mitogen (PWM)-activated autologous OKT4+ helper T cells in all four patients. Secretion of anti-MAG IgM by peripheral blood lymphocytes was dependent on the ratio of OKT4+ T helper cells to OKT8+ T suppressor/cytotoxic cells. In three patients with an OKT4+ to OKT8+ T-cell ratio of 2:1, PWM activation stimulated secretion of anti-MAG IgM; in one patient with an OKT4+ to OKT8+ ratio of 1:2, activation by PWM suppressed anti-MAG IgM secretion. These studies suggest that the monoclonal B cells that secrete anti-MAG IgM are responsive to regulatory T cells.

Production and characterization of monoclonal antibodies against myelin-associated glycoprotein

Monoclonal antibodies against myelin-associated glycoprotein were generated by fusing mouse myeloma cells with spleen lymphocytes from BALB/c mice immunized with human myelin-associated glycoprotein purified from CNS myelin. Three groups of antibodies were identified: IgG antibodies recognizing the polypeptide moiety and IgG and IgM antibodies recognizing the carbohydrate moiety of the intact molecule. Properties of these antibodies were examined with sodium dodecyl sulfate-polyacrylamide gel electrophoresis and the immunostaining technique using human CNS and peripheral nerve myelin, and ganglioside fractions isolated from human brain and peripheral nerve, and with immunohistochemical staining of human peripheral nerves. Part of human peripheral blood mononuclear cells was stained with the antibodies against the carbohydrate moiety, but not with IgG antibodies recognizing the polypeptide moiety. Natural killer activity was partially reduced after treatment of human peripheral blood lymphocytes with an IgM antibody and complement in vitro. The possibility that anti-myelin-associated glycoprotein antibodies might play a role in the pathogenesis of demyelinating diseases through modification of natural killer activity is discussed.

Sulfated glucuronyl glycolipids reacting with anti-myelin-associated glycoprotein monoclonal antibodies including IgM paraproteins in neuropathy: species distribution and partial characterization of epitopes

It was recently established that anti-myelin associated glycoprotein (MAG) IgM paraproteins associated with neuropathy and a substantial number of experimentally produced rat and mouse monoclonal antibodies that react with MAG (e.g. HNK-1) also bind to some sulfated glucuronic acid-containing sphingoglycolipids of human peripheral nerve. A species study revealed that these glycolipids could be detected readily by TLC overlay experiments in the acidic glycolipid fractions from human, monkey, bovine, cat and dog peripheral nerve. The glycolipids were also present in the nerves of rat, mouse, rabbit, guinea pig and chicken, but their concentration was about an order of magnitude lower. These antigenic glycolipids were present in the purified myelin fraction from cat nerve, but their level was not enriched over that in whole homogenate. Partial characterization of the epitopes in the glycolipids was accomplished by comparing binding of the human and experimental monoclonal antibodies to sulfated glucuronyl paragloboside (SGPG), to the desulfated lipid (GPG), and to the methyl ester of the desulfated lipid (MeGPG). All of the human, mouse and rat antibodies reacted with the intact SGPG, but none exhibited binding to MeGPG indicating that either the sulfate or the free carboxyl group on SGPG was required for reactivity. Five out of 11 human IgM paraproteins retained partial and variable reactivity with GPG showing that the sulfate was not absolutely required for binding, while the other 6 did not react with GPG. These results demonstrate idiotypic heterogeneity among the IgM paraproteins. Only 1 of 14 monoclonal antibodies produced experimentally in mice or rats retained reactivity with GPG.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of oligosaccharides that bind to human anti-MAG antibodies and to the mouse monoclonal antibody HNK-1

In some patients with neuropathy and IgM M-proteins the M-proteins bind to a carbohydrate determinant that is shared by the CNS and PNS myelin-associated glycoprotein (MAG) and by several additional glycoproteins and 2 glycolipids in peripheral nerve. The HNK-1 mouse monoclonal antibody binds to the same glycoproteins and glycolipids as well as to a number of other neuronal adhesion molecules and to human natural killer cells. To isolate the epitope-bearing oligosaccharides from their respective glycoproteins we digested delipidated spinal cord and peripheral nerve with pronase. The resulting glycopeptides were fractionated by concanavalin A-Sepharose chromatography to yield tri- and tetraantennary-complex, biantennary-complex and high mannose-type glycopeptides. Glycopeptides bearing the antigenic determinant were identified by their ability to block binding of M-proteins and HNK-1 antibodies to MAG-coated microwells by enzyme-linked immunosorbent assay (ELISA). Blocking activity was detected in the tri- and tetraantennary glycopeptide fraction from both CNS and PNS. The blocking activity was destroyed by pretreatment of the isolated glycopeptides with mild acid hydrolysis. Further fractionation by gel filtration chromatography indicated that the reactive glycopeptides from peripheral nerve and spinal cord eluted in the same position. The data suggest that CNS and PNS MAG and other peripheral nerve glycoproteins share similar oligosaccharides, and that the M-proteins and HNK-1 bind to the same structures.

The human anti-myelin-associated glycoprotein IgM system

Two mouse monoclonal antiidiotypic antibodies that react with human monoclonal IgM antibodies with specificity for myelin-associated glycoprotein (MAG) have been used to study the immunological specificity of the reported cross-reactions involving the anti-MAG IgM. Both of the antiidiotypic antibodies are shown to react with the combining site of their respective idiotypic IgM and to inhibit the reaction between IgM and MAG. Using these antiidiotypic antibodies as "surrogate" antigen, we have demonstrated immune cross-reactivity between MAG, a human peripheral nerve glycolipid, and a low-molecular-weight protein of human peripheral nerve myelin. In addition, we have used the two antiidiotypic antibodies to conduct a search for evidence of shared idiotypy among 34 different neuropathy-associated paraproteins. Our results provide no evidence for a neuropathy-associated idiotype, suggesting a degree of polymorphism in the human anti-MAG IgM system.

Reactivity with neural cell adhesion molecules in sera from patients with demyelinating diseases

Sera from 5 patients with IgM gammopathy and peripheral neuropathy reacted strongly by a sensitive immunospot enzyme-linked immunosorbent assay test with the myelin-associated glycoprotein (MAG) purified from human and bovine brains and the novel neural cell adhesion molecule J1 and associated glycoproteins from human brain. Two other members of the L2/HNK-1 family of cell adhesion molecules, the L1 glycoprotein and the neural cell adhesion molecule N-CAM, are not recognized significantly more strongly by these sera than by sera from patients with multiple sclerosis. Sera from patients with Guillain-Barré syndrome and amyotrophic lateral sclerosis and from healthy humans did not react with any of the glycoproteins tested at the serum concentrations used.

Monoclonal IgM in a patient with paraproteinemic polyneuropathy binds to gangliosides containing disialosyl groups

Monoclonal IgM kappa from a patient with polyneuropathy associated with paraproteinemia was found to bind to several polysialogangliosides. Binding of IgM to gangliosides was shown by enzyme-linked immunosorbent assay (ELISA) and by overlaying thin-layer chromatograms of human brain and peripheral nerve gangliosides with the patient's serum followed by radioiodinated goat antihuman IgM. The latter technique showed that the IgM paraprotein reacted with a number of gangliosides. In an ELISA the IgM paraprotein reacted strongly with GD2, GD3, GD1b, and GT1b, but not with GM1, GM3, and GD1a. Thus, the epitope for the patient's IgM paraprotein appears to involve the disialosyl configurations.

Human natural killer cell activity is reduced by treatment of anti-myelin-associated glycoprotein (MAG) monoclonal mouse IgM antibody and complement

Human mononuclear cells could be stained by anti-myelin-associated glycoprotein (MAG) monoclonal mouse IgM antibody. The remaining human natural killer (NK) cell activity examined by using K-562 cells at 20:1 as effector:target ratio after treatment of anti-MAG monoclonal mouse or anti-Leu-7 (HNK-1) antibody and complement revealed 13.4% and 15.1%, respectively (untreated NK activity was 40.8%). However, human NK activity could be abrogated by anti-Leu-11 and complement. The remaining NK activity shown as lytic units after treatment with anti-MAG, anti-Leu-7 or anti-Leu-11 and complement was 6.1, 5.3 and below 1.0, respectively (untreated NK cells showed 15.4). When NK activity was examined in another target cell, MOLT-4, the remaining activity shown as lytic units was also decreased with anti-MAG antibody (4.3) or with anti-Leu-7 (3.0) (untreated NK activity was 8.3). Our findings suggest that NK cells may be influenced by anti-MAG antibody if it is found in the sera as anti-lymphocytotoxic antibody.

The characterization and cellular distribution of a family of antigens related to myelin associated glycoprotein in the developing nervous system

The antigenic epitope detected on myelin associated glycoprotein (MAG) by the monoclonal antibody HNK-1 (Leu 7) was sensitive to degradation by trifluoromethane-sulfonic acid (TFMS) and is therefore probably carbohydrate in nature. This antigen was found to be widely distributed within the rat and chicken embryonic nervous system and was present on cultured central and peripheral neurons (100%), oligodendrocytes (100%) and astrocytes (70-80%) as detected by double marker immunofluorescence. The antigen could be removed from cultured neurons by trypsinization and its resynthesis was blocked by cycloheximide, suggesting that the carbohydrate epitope detected by HNK-1 was attached to a de novo synthesized protein. Several molecular species were detected on Western blots of detergent extracts from 13-15d rat embryonic brain and neuron-enriched cultures from chick spinal cord and dorsal root ganglia. Protein components with molecular weights in the ranges of 90-100 kd to 280 kd were observed and comprise a family of glycoproteins containing the HNK-1 reactive carbohydrate epitope present on MAG. These glycoproteins could play a role in intercellular interactions within the developing nervous system.

Polyneuropathy with monoclonal gammopathy: glycolipids are frequently antigens for IgM paraproteins

Immunoglobulins from patients with paraproteinemic polyneuropathy were screened for reactivity with nerve and brain glycolipids by ELISA and/or a thin-layer-chromatogram-overlay technique. The myelin-associated glycoprotein (MAG) has been shown to be an antigen in many neuropathy patients with IgM gammopathy, but this study focused on seven neuropathy patients in which the IgM paraproteins had been shown not to react with this glycoprotein. Five of these seven had IgM that reacted with components in the acidic glycolipid fraction of human sciatic nerve, and three of these IgMs also reacted with components in the acidic glycolipid fraction of human brain. Little or no reactivity with glycolipids was detected for two patients with neuropathy and IgG gammopathy or for two with neuropathy and IgA gammopathy. The results suggest that neuropathy-patient IgM paraproteins not reactive with MAG often react with acidic glycolipids and thus define a subset of paraproteinemic neuropathies. Since the IgM paraproteins that react with MAG also react with acidic glycolipids of nerve, glycolipid antigens appear to be quite common among the IgM paraproteinemic neuropathies.

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.

Pattern of reactivity of IgM from the sera of eight patients with IgM monoclonal gammopathy and neuropathy with components of neural tissues: evidence for interaction with more than one epitope

It has been postulated that binding of monoclonal IgM from the sera of some patients with IgM monoclonal gammopathy and neuropathy to components of peripheral nerve may play a key role in the pathogenesis of the neuropathy. Serum IgM from these patients has been shown to bind to antigenic determinants shared by the myelin-associated glycoprotein (MAG) and a polar glycolipid from peripheral nerve. Here we describe a study of sera from eight patients with IgM monoclonal gammopathy and neuropathy. Five of the patients had serum IgM directed both against MAG and one or two polar glycolipids from peripheral nerve. One of the patients had serum IgM that bound to a peripheral nerve glycolipid but not to MAG; no one had serum IgM that bound to MAG but not to a peripheral nerve glycolipid. The relative affinity of IgM from the sera of the patients for proteins in peripheral nerves of chickens, dogs, and humans varied from patient to patient. These data indicate that the epitope against which the serum IgM from these patients is directed is not necessarily the same in all of the cases.