Peripheral nervous system myelin and Schwann cell glycoproteins: identification by lectin binding and partial purification of a peripheral nervous system myelin-specific 170,000 molecular weight glycoprotein

Localization of major gangliosides in the PNS: implications for immune neuropathies

Antibodies targeting major gangliosides that are broadly distributed in the nervous system are sometimes associated with clinical symptoms that imply selective nerve damage. For example, anti-GD1a antibodies are associated with acute motor axonal neuropathy (AMAN), a form of Guillain-Barré syndrome that selectively affects motor nerves, despite reports that GD1a is present in human axons and myelin and is not expressed differentially in motor versus sensory roots. We used a series of high-affinity monoclonal antibodies (mAbs) against the major nervous system gangliosides GM1, GD1a, GD1b and GT1b to test whether any of them bind motor or sensory fibres differentially in rodent and human peripheral nerves. The following observations were made. (i) Some of the anti-GD1a antibodies preferentially stained motor fibres, supporting the association of human anti-GD1a antibodies with predominant motor neuropathies such as AMAN. (ii) A GD1b antibody preferentially stained the large dorsal root ganglion (DRG) neurones, in keeping with the proposed role of human anti-GD1b antibodies in sensory ataxic neuropathies. (iii) Two mAbs with broad structural cross-reactivity bound to both gangliosides and peripheral nerve proteins. (iv) Myelin was poorly stained; all clones stained axons nearly exclusively. Our findings suggest that anti-ganglioside antibody fine specificity as well as differences in ganglioside accessibility in axons and myelin influence the selectivity of injury to different fibre systems and cell types in human autoimmune neuropathies.

Antibodies to L-periaxin in sera of patients with peripheral neuropathy produce experimental sensory nerve conduction deficits

L-Periaxin is a PDZ-domain protein localized to the plasma membrane of myelinating Schwann cells and plays a key role in the stabilization of mature myelin in peripheral nerves. Mutations in L-periaxin have recently been described in some patients with demyelinating peripheral neuropathy, suggesting that disruption of L-periaxin function may result in nerve injury. In this study, we report the presence of autoantibodies to L-periaxin in sera from two of 12 patients with diabetes mellitus (type 2)-associated neuropathy and three of 17 patients with IgG monoclonal gammopathy of undetermined significance (MGUS) neuropathy, an autoimmune peripheral nerve disorder. By comparison, anti-L-periaxin antibodies were not present in sera from nine patients with IgM MGUS neuropathy or in sera from 10 healthy control subjects. The effect of anti-L-periaxin serum antibody on peripheral nerve function was tested in vivo by intraneural injection. Sera containing anti-L-periaxin antibody, but not sera from age-matched control subjects, injected into the endoneurium of rat sciatic nerve significantly (p < 0.005, n = 3) attenuated sensory-evoked compound muscle action potential (CMAP) amplitudes in the absence of temporal dispersion. In contrast, motor-evoked CMAP amplitudes and latencies were not affected by intraneural injection of sera containing anti-L-periaxin antibody. Light and electron microscopy of anti-L-periaxin serum-injected nerves showed morphologic evidence of demyelination and axon enlargement. Depleting sera of anti-L-periaxin antibodies neutralized the serum-mediated effects on nerve function and nerve morphology. Together, these data support anti-L-periaxin antibody as the pathologic agent in these serum samples. We suggest that anti-L-periaxin antibodies, when present in sera of patients with IgG MGUS- or diabetes-associated peripheral neuropathy, may elicit sensory nerve conduction deficits.

Identification of Gal(beta 1-3)GalNAc bearing glycoproteins in cerebrospinal fluid of amyotrophic lateral sclerosis (ALS) patients

Glycoproteins in cerebrospinal fluid of 55 patients with amyotrophic lateral sclerosis (ALS), six disease controls (multifocal motor neuropathy, sensorimotor neuropathy, Guillain-Barré syndrome, spinal muscular atrophy type II, motor neuropathy with monoclonal gammopathy) and 20 healthy controls were separated by PAGE electrophoresis and then detected immunochemically with peanut agglutinin (PNA). In 36 amyotrophic lateral sclerosis patients the 262 kDa glycoprotein was significantly increased (over the normal mean +/- SD x 2), which was associated with a decrease in the 114 kDa fraction. In the remaining patients, both fractions were either equal in concentration or the 114 kDa glycoprotein predominated. In normal cerebrospinal fluid, the 114 kDa glycoprotein predominated over the other glycoproteins. The total amount of separated glycoproteins was increased in 15 amyotrophic lateral sclerosis patients. In 12 of them it was followed by an increase in the percentage of the 262 kDa glycoprotein. There was no correlation between the content of the peanut agglutinin-labelled glycoproteins and the patients' age, duration and severity of the disease. There was a correlation between the 262 kDa glycoprotein being increased in cerebrospinal fluid and the electrophysiological pattern of denervation seen in electromyographic study. The glycoproteins change, similar to that occurring in amyotrophic lateral sclerosis patients, was also observed in one case of multifocal motor neuropathy (MMN). We suggest that in amyotrophic lateral sclerosis and multifocal motor neuropathy, the peanut agglutinin-labelled glycoproteins are released in excess from the nervous tissues into the cerebrospinal fluid as a result of neuronal degeneration. The question to be answered is, whether the released glycoproteins are becoming targets for auto-antibodies.

Immunochemical quantification of glycoconjugates in serum and cerebrospinal fluid of amyotrophic lateral sclerosis patients

Glycoconjugates in the serum of 73 patients with amyotrophic lateral sclerosis (ALS), 21 cases of other motor neuron diseases and 20 healthy controls were determined. Cerebrospinal fluid (CSF) was studied in 64, 7 and 10 of these subjects, respectively. The level of sialic acid containing glycoconjugates, detected by Maakia amurensis agglutinin (MAA), was decreased in the serum of 61.6% of the ALS patients, while in the CSF it was decreased, on average, in 75% of these cases. Only in single ALS cases was the concentration of these glycoconjugates increased. There was no correlation between the content of MAA-labelled glycoconjugates both in serum and CSF and the titre of sialic acid containing anti-GM1 gangliosides. The glycoconjugates, detected by peanut agglutinin (PNA) which recognizes the disaccharide galactose beta(1-3)N- acetylgalactosamine (GGN), were decreased in the serum of 78.1% of ALS patients, while in CSF they were increased in 54.7% of these cases. There was no correlation between the concentration of PNA-labelled glycoconjugates both in serum and CSF as well as the titre of antibodies against GGN-containing anti-GM1 and anti- AGM1 gangliosides. Changes in the level of the MAA- and PNA- labelled glycoconjugates, as well as the titre of anti-GM1 and anti-AGM1 gangliosides antibodies were not specific for ALS. They were also observed in some cases of other motor neuron diseases. The low level of the lectin-labelled glycoconjugates in serum and partly in CSF of the majority of ALS patients is possibly the consequence of their accelerated clearance and/or specific inactivation by the formation of immune complexes or epitope binding. Degeneration of neurons and muscle cells could also be responsible. The relatively low incidence of high anti- glycolipids antibodies titre may be, at least partly, connected with the low concentration of the appropriate antigens. The increased content of PNA-labelled glycoconjugates in the CSF of the majority of ALS patients, together with the low incidence of high titre of antibodies against the appropriate glycolipids, could indicate that in CSF this lectin binds to the GGN epitope of glycoproteins rather than to the GGN epitope of glycolipids.

The distribution of ganglioside-like moieties in peripheral nerves

GM1 ganglioside has been implicated as a target of immune attack in some diseases of the peripheral nervous system. Anti-GM1 ganglioside antibodies are associated with certain acquired immune-mediated neuropathies. It is not clear how anti-GM1 antibodies cause nerve dysfunction and injury; however, sodium and/or potassium ion channel dysfunction at the node of Ranvier has been implicated. To gain insight into the pathogenesis of these neuropathies, we examined the distribution of GM1 ganglioside and Gal(beta1-3)GalNAc moieties in nerve fibres and their relationship to voltage-gated sodium and potassium (Kv1.1, 1.5) channels at the nodes of Ranvier in peripheral nerves from human, rat and dystrophic mice. Gal(beta1-3)GalNAc moieties were localized via the binding of cholera toxin and peanut agglutinin. As a control for the specificity of these findings, we compared the distribution of GM1 moieties to that of the ganglioside GT1b. Our study provides definitive evidence for the presence of Gal(beta1-3)GalNAc bearing moieties on the axolemmal surface of mature myelinated fibres and on Schwann cells. Gal(beta1-3)GalNAc binding sites did not have an obligatory co-localization with voltage-gated sodium channels or the potassium ion channels Kv1.1 and Kv1.5 and are thus not likely carried by these ion channels. In contrast with Gal(beta1-3)GalNAc, GT1b-like moieties are restricted to the axolemma.

Glycoproteins of myelin sheaths

A growing number of glycoproteins have been identified and characterized in myelin and myelin-forming cells. In addition to the major P0 glycoprotein of compact PNS myelin and the myelin-associated glycoprotein (MAG) in the periaxonal membranes of myelin-forming oligodendrocytes and Schwann cells, the list now includes peripheral myelin protein-22 (PMP-22), a 170 kDa glycoprotein associated with PNS myelin and Schwann cells (P170k/SAG), Schwann cell myelin protein (SMP), myelin/oligodendrocyte glycoprotein (MOG), and oligodendrocyte-myelin glycoprotein (OMgp). Many of these glycoproteins are members of the immunoglobulin superfamily and express the adhesion-related HNK-1 carbohydrate epitope. This review summarizes recent findings concerning the structure and function of these glycoproteins of myelin sheaths with emphasis on the physiological roles of oligosaccharide moieties.

Antibodies to GM1 and Gal(beta 1-3)GalNAc at the nodes of Ranvier in human and experimental autoimmune neuropathy

Autoantibodies to Gal(beta 1-3)GalNAc epitopes on glycolipids and glycoproteins are associated with motor neuron disease and motor or sensorimotor neuropathy. These epitopes are ubiquitously distributed on cell surfaces. In the nervous system they are present on axons and myelin, specifically also at the nodes of Ranvier. Binding of GM1 antibodies to the nodal area may contribute to disease development in some of these conditions.

Lectin histochemistry of normal and neoplastic peripheral nerve sheath. 1. Lectin binding pattern of normal peripheral nerve in man

The binding patterns of lectins to normal peripheral nerves were examined. Twelve biotinylated lectins were used in this study; Canavalia ensiformis (Con A), Pisum sativum (PSA), Lens culinaris (LCA), Ricinus communis 1 (RCA-1), Arachis hypogaea (PNA), Glycine max (SBA), Sophora japonica (SJA), Bandeiraea simplicifolia 1 (BSL-1), Triticum vulgaris (WGA), succinylated WGA (s-WGA), Ulex europaeus 1 (UEA-1) and Helix pomatia (HPA). Cytoplasm of Schwann cells and perineurial cells was stained by Con A, PSA, LCA, s-WGA and WGA. PNA showed specific binding to perineurial cells, while after neuraminidase treatment stain with this lectin was demonstrated also in Schwann cells. Myelin sheaths were stained with fewer lectins. SBA and HPA with sialic acid removal rarely showed reactivity to the peripheral nerve structure in surgical specimens, in contrast to clear staining of Schwann cells, perineurial cells and myelin sheaths in autopsy specimens. The present study shows distinct lectin stainings of specific structures of the normal human peripheral nerves, and provides important basic information on the alterations of lectin binding patterns during pathological processes in the peripheral nerves.

Glycosphingolipids of human peripheral nervous system myelins isolated from cauda equina

Compositions of neutral and sulfated glucuronyl glycosphingolipids purified from human motor and sensory nerves and myelins were studied. Higher neutral glycosphingolipids (fraction B), which were separated from GalCer (fraction A), were analyzed by TLC and TLC-immunostaining. Both nerve myelins contained paragloboside (nLc4Cer) and nLc6Cer dominantly as major higher glycosphingolipids and very little globoside (Gb4Cer), whereas both nerves contained Gb4Cer and nLc4Cer. Besides these major glycosphingolipids, a neutral glycolipid containing asialoGM1 (Gg4Cer) epitope and other minor components such as ceramide trihexoside and ceramide dihexoside were detected in both nerves and their myelins. Furthermore, sulfated glucuronyl nLc4Cer and nLc6Cer, which were monoclonal antibody HNK-1 reactive glycolipids, were detected in both nerves and myelins.

Anti-GM1 IgA antibodies in Guillain-Barré syndrome

Serum anti-GM1 IgA antibodies were detected in 15 of 53 (28%) patients with the acute Guillain-Barré syndrome (GBS) and in one of 26 (4%) patients with other neurological diseases. Although nine GBS patients had anti-GM1 IgA titers of 1:200 or less, six patients had titers of 1:800 or more. Some GBS patients with anti-GM1 IgA antibodies also had antibodies against GD1b or GM2 or both. The presence of markedly elevated anti-GM1 IgA was associated with a poor clinical outcome at 6 and 12 months following onset of the GBS. The possible pathogenetic role of anti-GM1 IgA antibodies remains to be established.

Invited review: motor neuropathies, motor neuron disorders, and antiglycolipid antibodies

High titers of IgM anti-GM1 antibodies are commonly found in the serum of patients with some lower motor neuron disorders and peripheral neuropathies. Enzyme-linked immunosorbent assays (ELISA) are useful for the detection and quantitation of anti-GM1 antibodies. Testing for serum anti-GM1 activity is indicated in the diagnostic evaluation of lower motor neuron syndromes. The presence of high titers of anti-GM1 antibodies mandates careful electrophysiologic testing for the motor conduction block that is found in multifocal motor neuropathy, a treatable disorder. Quantitation of anti-GM1 antibodies may also be a useful guide in the treatment of multifocal motor neuropathy. Further study of antiglycolipid antibodies in motor neuron disorders and peripheral neuropathies may provide clues to the events that stimulate these antibodies and to the pathogenesis of such syndromes.

Autoantibodies to GM1 ganglioside: different reactivity to GM1-liposomes in amyotrophic lateral sclerosis and lower motor neuron disorders

We studied the ability of anti-GM1 ganglioside antibodies to bind to GM1 in a lipid, "membrane-like" environment. Liposomes containing GM1 were synthesized to simulate this environment. We then compared the binding of anti-GM1 a autoantibodies to GM-1-liposomes and to purified GM1. Antibody binding was quantitated using enzyme-linked immunosorbent assay methodology. Our results showed a 250-fold variation in the ability of anti-GM1 antibodies to bind to GM1-liposomes. There was no correlation between GM-1-liposome binding and the carbohydrate specificities of the anti-GM1 antibodies. However, anti-GM1 antibodies from patients with amyotrophic lateral sclerosis (ALS) showed a 4 fold greater binding to GM1-liposomes than antibodies from patients with lower motor neuron (LMN) syndromes. We conclude that a lipid, presumably "membrane-like", environment may greatly influence the degree of anti-GM1 antibody binding to GM1. The low levels of anti-GM1 antibody binding to GM1-liposomes in patients with LMN syndromes may provide a diagnostic means for distinguishing these patients from those with ALS. Anti-GM1 antibodies from patients with ALS may bind especially well to neuronal membranes containing GM1 in vivo.

Effects of inhibitors of oligosaccharide processing on P0 protein synthesis and incorporation into PNS myelin

Four inhibitors of oligosaccharide processing were used to investigate their effects on the transport of PNS myelin glycoproteins through the secretory pathway, as well as to gain further insight into the structure of the oligosaccharide chains of the P0 and 19-kDa glycoproteins. Several different inhibitors of oligosaccharide processing were incubated with chopped peripheral nerves from young rats (21-24 days of age) and the uptake of 14C-amino acid and [3H]fucose or [3H]mannose was measured in P0 and the 19-kDa glycoprotein after separation of homogenate and myelin proteins on polyacrylamide gels. [3H]Mannose was not found as suitable as [3H]fucose as an oligosaccharide precursor because glucose used as an energy source profoundly inhibited the uptake of [3H]mannose. The substitution of pyruvate as an energy source, however, resulted in incomplete glycosylation, poor amino acid uptake, and truncated oligosaccharide chains. Endoglycosidase H cleaved approximately 50% of the P0 labeled with [3H]fucose and 14C-amino acid. The lower molecular weight protein resulting from endoglycosidase H cleavage contained approximately one-half the [3H]fucose label on the protein, whereas one-half remained on the oligosaccharide chain of the undegraded P0, indicating that at least one-half the P0 has a hybrid structure. Deoxynojirimycin, deoxymannojirimycin, and castanospermine inhibited incorporation of [3H]fucose into the oligosaccharide chains of P0 and the 19-kDa glycoprotein as predicted from their action in blocking various stages of trimming of high mannose structures before the addition of fucose. P0 synthesized in the presence of these inhibitors was cleaved to a greater extent by endoglycosidase H than the normal protein, indicating increased vulnerability to this enzyme with arrest of normal processing. Similar results were obtained for the 19-kDa glycoprotein. Both the incompletely processed P0 and the 19-kDa glycoprotein formed in the presence of these inhibitors appeared to be transported normally into myelin.

Search for antibodies to neutral glycolipids in sera of patients with Guillain-Barré syndrome

Sera from 54 patients with Guillain-Barré syndrome (GBS), 34 patients with other neurological diseases (OND) and 32 healthy controls were tested for antibodies to total lipid fractions and higher neutral glycolipid fractions isolated from human and dog nerves, purified Forssman glycolipid and a panel of purified neutral glycolipids by both an enzyme-linked immunosorbent assay (ELISA) and a thin-layer chromatogram (TLC)-overlay technique. IgM and IgG antibodies to total lipid fractions, as well as to galactocerebroside, ceramide dihexoside, ceramide trihexoside, and globoside were not significantly elevated in the sera of GBS patients as compared to controls. High levels of anti-asialo-GM1 IgG antibodies, however, were detected in 6 of 54 (11%) GBS patients and 1 of 30 (3%) OND patients. Intense reactivity with purified Forssman glycolipid and a number of glycolipid antigens in higher neutral glycolipid enriched fractions of human cauda equina and dog sciatic nerves was noted by TLC-immunostaining in many GBS and control sera. Although the levels of anti-Forssman IgM were significantly decreased in GBS sera compared with normal sera (P less than 0.05) and OND sera (P less than 0.02), the levels of anti-Forssman IgG antibodies were not significantly different. With the possible exception of IgG antibodies to asialo-GM1, our results suggest that serum antibodies against Forssman glycolipid and neutral glycolipids are not significantly elevated in GBS patients and, thus, are unlikely to play an important role in the pathogenesis of this disease.

Cleavage of the P0 glycoprotein of the rat peripheral nerve myelin: tentative identification of cleavage site and evidence for the precursor-product relationship

The incubation of sciatic nerve slices in Krebs Ringer bicarbonate (KRB) buffer (pH 7.4) at 37 degrees C, or the incubation of freshly isolated myelin in ammonium bicarbonate buffer (pH 8), resulted in the generation of a 24 kDa protein with a concomitant decrease of P0 protein. The conversion of P0 into 24 kDa protein was blocked by heating isolated myelin at 100 degrees C for 5 min suggesting that the reaction is enzyme mediated. Inclusion of the protease inhibitors and chelating agent to isolated myelin did not prevent the formation of 24 kDa protein. Similarly, addition of CaCl2 to isolated myelin did not accentuate the formation of 24 kDa protein suggesting that the conversion of P0 into 24 kDa protein may not be due to Ca2+ activated protease. It is postulated that the formation of 24 kDa protein may be due to neutral protease and/or metalloproteinase associated with the PNS myelin. 24 kDa protein was purified and characterized. The N-terminal sequence of 1-17 amino acid residues of 24 kDa protein was identical to P0. 24 kDa protein was immunostained and immunoprecipitated with anti-P0 antiserum indicating the immunological similarities between P0 and 24 kDa protein. Labeling of 24 kDa protein with [35S]methionine provided evidence that P0 may be in all probability cleaved between Met-168 and Met-193. Further studies were carried out to demonstrate that 24 kDa protein was phosphorylated, glycosylated and acylated like P0. Phosphorylation of 24 kDa protein in the nerve slices was increased five-fold by phorbol esters and phosphoserine was the only phosphoamino acid identified after partial acid hydrolysis of 24 kDa protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Lower motor neuron syndromes defined by patterns of weakness, nerve conduction abnormalities, and high titers of antiglycolipid antibodies

We studied 74 patients with progressive, asymmetrical lower motor neuron syndromes. Clinical features of these patients, including age, sex, disease duration, patterns of weakness, and reflex changes, were evaluated by review of records. In each patient the clinical features were compared to the type of nerve conduction abnormalities and to the specificities of high-titer serum antiglycolipid antibodies. Antibody specificities were determined by an enzyme-linked immunosorbent assay using purified glycolipids and carbohydrates as substrates. Our results show that high titers of antibodies to glycolipids are common in sera of patients with lower motor neuron syndromes. Selective patterns of reactivity indicate that specific carbohydrate epitopes on the glycolipids are the targets of the high-titer antibodies in individual patients with lower motor neuron syndromes. Several distinct lower motor neuron syndromes can be identified based on clinical, physiological, and antiglycolipid antibody characteristics. These syndromes include multifocal motor neuropathy with evidence of multifocal conduction block on motor, but not sensory, axons and frequent (84%) high titers of anti-GM1 ganglioside antibodies; a lower motor neuron syndrome with predominantly distal weakness early in the disease course, no conduction block, and a high incidence (64%) of anti-GM1 antibodies; and a lower motor neuron syndrome with predominant early weakness in proximal muscles and serum antibodies to asialo-GM1 that do not cross-react with GM1 ganglioside.

Neuropathy and anti-GM1 antibodies

Increased titers of IgM antibodies that react with carbohydrate epitopes on GM1 are present in some patients with lower motor neuron disease, sensorimotor neuropathy, or motor neuropathy with or without conduction block. Therapeutic reduction of antibody concentrations can result in clinical improvement, suggesting that the antibodies may be pathogenic. The anti-GM1 antibodies react with carbohydrate epitopes, which are shared by several other glycolipids and glycoproteins in the central and peripheral nervous system. The antibodies might exert their effects at a number of sites, depending on the topographical distribution of the target antigens and on their accessibility. B-cells that express anti-GM1 antibodies are present at birth and are normally suppressed or rendered anergic. Under some circumstances, however, they might be activated to secrete autoantibodies that cause autoimmune neuropathy.

Monoclonal IgMs with anti-Gal(beta 1-3) GalNAc activity in lower motor neuron disease; identification of glycoprotein antigens in neural tissue and cross-reactivity with serum immunoglobulins

IgM monoclonal antibodies (M-proteins) with anti-Gal(beta 1-3)GalNAc and anti-Gal(beta 1-3)GlcNAc activity that bind to gangliosides GD1b and GM1, from two patients with lower motor neuron disease were tested for binding to neural glycoproteins. The M-proteins bound to several glycoproteins in the central and peripheral nervous system including to some in the non-myelin or axonal fraction only. Peanut agglutinin (PNA) which is specific for Gal(beta 1-3)GalNAc, bound to the same protein bands. Since serological studies revealed that the M-proteins were complexed to IgG, serum immunoglobulins were tested for presence of Gal(beta 1-3)GalNAc epitopes. Both PNA and the M-proteins bound to immunoglobulin heavy and light chains, suggesting that the circulating M-proteins bind to Gal(beta 1-3)GalNAc on other immunoglobulins. These studies indicate that in addition to gangliosides the M-proteins might bind to Gal(beta 1-3)GalNAc bearing glycoproteins in vivo and that carbohydrate epitopes on immunoglobulins might have a role in the development and regulation of autoantibodies which cross-react with neural antigens and may cause neurological disease.

Comparative histochemical and biochemical analysis of endogenous receptors for glycoproteins in human and pig peripheral nerve

Endogenous sugar-binding proteins were localized in sections of human and pig peripheral nerves by the application of two types of labelled ligands: neoglycoproteins (chemically glycosylated carrier proteins that had proven to be histochemically inert) and desialylated, naturally occurring glycoproteins. These proteins allowed evaluation of the presence and distribution of endogenous receptors for carbohydrates, commonly present in cellular glycoconjugates. (Neo)glycoprotein binding was similar, but not identical, for the two types of mammalian peripheral nerves. The pig nerve differed from the human nerve in more pronounced staining when using different types of beta-galactoside-terminated (neo)glycoproteins and charge-carrying neoglycoproteins, such as bovine serum albumin, bearing galactose-6-phosphate residues, glucuronic acid residues, and sialic acid residues. Comparative biochemical analysis of certain classes of sugar receptors by affinity chromatography and gel electrophoresis revealed the presence of sugar receptors that can contribute to the histochemical staining in a pattern with certain significant differences among rather similar expression for the two species. The assessment of sugar receptor distribution by application of (neo)glycoprotein binding among morphologically defined regions in nerves may hold promise in detecting developmental regulation and changes during nerve degeneration and subsequent regeneration after trauma or pathological states. Correlation of these results to changes in the structure and abundance of glycoconjugates, which are the potential physiological ligands of endogenous sugar receptors commonly detected by plant lectins, may help to infer functional relationships.

A cyclic AMP analogue induces synthesis of a myelin-specific glycoprotein by cultured Schwann cells

Neonatal rat Schwann cells, cultured with agents which increase intracellular cyclic AMP, were prompted to resume synthesis of a 170,000 Mr glycoprotein which is specific to peripheral nervous system myelin and is herein referred to as P170K. We have shown previously that similar treatment induces the synthesis by Schwann cells of the myelin lipid, galactocerebroside. In contrast to P170K and galactocerebroside, syntheses of P0 and myelin basic protein were not induced. Intracellular cyclic AMP is thus likely to be a participant in the complex system regulating myelination.

Immunological nonidentity of 19K protein and TP0 in peripheral nervous system myelin

Peripheral nervous system myelin contains as the major structural protein a glycoprotein known as P0. Another glycoprotein present in smaller amounts, known as the 19K or X protein, has been previously identified as derived from P0 and identical with the main tryptic degradation product of P0 (TP0). Although both P0 and 19K protein incorporated fucose in vitro and stained on polyacrylamide gels with the periodic acid-Schiff stain for carbohydrate, only the P0 blotted to nitrocellulose paper showed immunoreactivity to an antibody to P0, whereas the 19K protein did not. Furthermore, when P0 was hydrolyzed with trypsin or elastase, the main degradation products reacted with P0 on immunoblots, whereas the 19K protein showed no immunoreactivity. From these studies and those of others, it may be concluded that the 19K protein shows some similarities to TP0, but probably has a different structure. P0 and 19K protein do not appear to be related as shown by lack of cross-immunoreactivity.

Immunochemical characterization of peripheral nervous system myelin 170,000-Mr glycoprotein

A recently described 170,000-Mr glycoprotein, specific to peripheral nervous system (PNS) myelin, was purified from rat PNS myelin by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis and used to immunize guinea pigs and rabbits. The resultant antisera proved specific for 170,000-Mr glycoprotein by enzyme-linked immunosorbent assay, by immunoprecipitation of the appropriate peptide from solubilized PNS myelin, and by immunoblot analysis of rat PNS myelin. The anti-rat 170,000-Mr glycoprotein antisera cross-reacted with proteins of similar molecular weight in human and bovine PNS myelin, but such proteins were not detected in human or rat CNS myelin or other rat tissues. The 170,000-Mr glycoprotein was also detected by this immunoblot procedure in recently isolated rat Schwann cells but not in those kept in culture for greater than or equal to 3 days. By indirect immunofluorescent microscopy, anti-rat 170,000-Mr glycoprotein antibody bound to rat PNS myelin sheaths but not to other rat tissues. Together, these studies indicate the 170,000-Mr glycoprotein is specific to PNS myelin of several species and that a neuronal influence may be required for its expression by Schwann cells.

Localizations of ruthenium red positive material in rabbit peripheral nerves

The penetration and distribution of ruthenium red in the axon-myelin-Schwann cell complex of developing rabbit peripheral nerve fibers are investigated. Ruthenium red positive material is established in the axoplasm, axolemma, periaxonal space, major dense lines and intraperiod lines of the compact myelin, mesaxons, split peripheral myelin lamellae, Schmidt-Lanterman and longitudinal incisures, paranodal loops and axo-glial contacts, Schwann cell cytoplasm and basal lamina, nodal extracellular matrix, desmosome-like structures, endoneural collagen. Some features of the distribution of the contrast material in the developing myelin sheath are described. Regional differences of the axolemma and of the Schwann cell cytoplasm and plasmalemma are established. The prevalence of glycoproteins or glycolipids in the ruthenium red stained material in its different localizations is discussed on the basis of trypsin and hyaluronidase digestion performed.

The role of non-resident cells in Wallerian degeneration

Wallerian degeneration was studied in the phrenic or sciatic nerves of mice following transplantation into Millipore diffusion chambers of 0.22 micron pore size which were implanted in the peritoneal cavity and kept for up to eight weeks. This method positively eliminates the access of nonresident cells to the tissue, at the same time providing proper conditions for tissue survival. Such nerves showed no proliferation of Schwann cells and no evidence for their active role in the removal or digestion of myelin. Schwann cells rejected their sheaths and the latter persisted for weeks, leading either to sheath distension (the sheath becoming wider and thinner) or to collapse (the sheath becoming thicker, collapsing upon the empty axis cylinder). The outer envelope of Schwann cytoplasm separated into pseudopodia rich in microtubules. Sheath rejection led to a slow decay of the myelin in the absence of active phagocytosis. There was profuse fibroblastic proliferation from the epineurium and perineurium, from which cells migrated into the chambers developing fatty change. No evidence was found to link the fatty change in fibroblasts to sheath decay. Diffusion chambers of 5.0 micron pore size were invaded by leukocytes and monocytes. Nerves kept in such chambers showed active phagocytosis of myelin leading to its removal, similar to Wallerian degeneration in situ. Phagocytes were shown to attack selectively the rejected myelin sheaths, distinguishing the latter from the surviving Schwann cells, even though both structures derive from the same cell. The activity of phagocytes in digesting myelin was mediated by a signal which diminished in intensity with time; there was very little active phagocytosis of myelin in nerves that had been predegenerated in 0.22 micron pore chambers. Various modifications of the experiment, including studies with co-cultured peritoneal macrophages or bone marrow, indicate a need for additional activating factors to induce myelin phagocytosis.