A novel cholinergic-specific antigen (Chol-2) in mammalian brain

Three new antisera have been raised in sheep against cholinergic electromotor presynaptic plasma membranes prepared from the electric organs of the electric ray, Torpedo marmorata. They all recognized one or more cholinergic-specific antigens in the mammalian nervous system by the following criteria: they sensitized the cholinergic subpopulation of rat-brain synaptosomes--and only this subpopulation--to lysis by the complement system and, in an immunocytochemical study, selectively stained choline acetyltransferase-positive cholinergic neurons in the rat spinal cord. However, two of the three antisera failed to recognize Chol-1 alpha and -beta, two closely related minor gangliosides already identified as the cholinergic-specific antigens recognized by previous anti-Torpedo presynaptic plasma membrane antisera or indeed any other ganglioside and the third recognized only Chol-1 alpha. A further investigation of the antigen(s) recognized by the most antigenic of the new antisera indicated that it is proteinaceous in nature, but has epitopes in common with electric organ gangliosides.

Immunological identification of a Cl- channel protein in electric organs of Narke japonica

A Cl- channel in electric organs of Narke japonica was reconfirmed, using a polyclonal antibody, to be a 180k protein composed of two identical 90k units. The specific antibody against the 180k protein from electric organs reduced, when added in the cis side solution, the open probability of the Cl- channel in a planar bilayer membrane without affecting the single channel conductance, ion selectivity nor voltage dependency. Furthermore, the antibody added in the trans side also affected the channel to increase the open probability. The eluate of the immuno-affinity chromatography was found to contain only the 180k protein. These results indicate that 180k protein to be an integral membrane protein and to form the Cl- channel.

Suppression of experimental autoimmune myasthenia gravis with new immunosuppressants: 15-deoxyspergualin and actinobolin

In the search for a new drug to treat myasthenia gravis, we studied the efficacy of new immunosuppressants on experimental autoimmune myasthenia gravis (EAMG). 15-Deoxyspergualin (15-DSP), bactobolin and actinobolin were administered to some groups at the time of immunization and to other groups 10 days after. The most effective results were achieved with doses of 2.5 mg/kg daily of 15-DSP and 30 mg/kg daily of actinobolin administered from day 1. In both groups, the body weights of the rats increased as normally as those of controls and signs of myasthenia were mild. Immunoelectron microscopic examination of the neuromuscular junctions in rats treated with 2.5 mg/kg of 15-DSP appeared normal, even in the chronic phase (induced by a booster at week 4). Levels of anti-acetylcholine receptor antibodies were almost completely suppressed. Although the effects of these drugs were more remarkable when administered from day 1 than from day 10, the results suggest that they may prove useful in treating myasthenic patients.

Monoclonal antibody Tor 23 binds a subset of neural cells in the human cortex and displays an altered binding distribution in Alzheimer's disease

Recent evidence suggests that alterations in molecules of the external neuronal surface may be pivotal factors in Alzheimer's disease (AD) either as primary or secondary lesions. We are studying neuronal surface components with a library of monoclonal antibodies (MAbs) made to highly purified, exclusively cholinergic nerve terminals of the Torpedo ray. The most extensively characterized of the Tor MAbs. Tor 23, binds the external membrane of some human neuronal cells in culture. Our present findings demonstrate that Tor 23, in situ, binds the apparent limiting membrane of rare neurons of the human isocortex. Tor 23 binds, in addition, internally within a subpopulation of subcortical white matter astrocytes, as identified by colocalization with glial fibrillary acidic protein. Neuronal surface binding of Tor 23 parallels our findings in other species: astrocyte staining was not observed in other species and may be unique to human. Immunoblot analysis of white matter reveals one polypeptide band with a relative mobility of 115,000 +/- 15,000 daltons. In the mid-frontal cortex from cases of AD. Tor 23 immunopositive neurons are greatly reduced in number and immunopositive astrocytes are completely absent. The reduction of the neuronal surface epitope defined by Tor 23 supports the recent hypothesis that surface molecules are altered in AD. The absence of Tor 23 positive astrocytes opens an area for specific investigation: namely, the role subcortical astrocytes may play in the pathogenesis of AD.

Monoclonal antibodies against the main immunogenic region of the acetylcholine receptor. Mapping on the intact molecule

About two-thirds of the antibodies to the nicotinic acetylcholine receptor (AChR) in myasthenic patients, and in rats immunized with intact AChR, bind to the main immunogenic region (MIR) on the alpha-subunit. We tested all available anti-MIR monoclonal antibodies (mAbs) by competition experiments for binding on the intact AChR from Torpedo electric organ and human muscle. Practically complete competition between all possible paired combinations of anti-MIR mAbs was found. As a consequence, the MIR must be a very concrete and small region. Furthermore, the location of the MIR relative to some other less immunogenic regions was also determined.

Immunization of rats with cholinergic neurons induces behavioral deficits

We have previously shown that sera from patients with Alzheimer's disease (AD) contain a significantly high level of antibodies to the cell bodies (Perikarya; PK) but not to the nerve terminals (synaptosomes) of purely cholinergic neurons from the electric fish Torpedo. In the present study we examined the effect of repeated immunization of rats with either of these antigens for one year. Immunoblot studies revealed that sera of cholinergic PK immunized rats contained a high level of antibodies to cholinergic PK proteins, in particular to a 200 kilodalton protein, to which there are specifically high levels of antibodies in AD. Sera from rats immunized with cholinergic synaptosomes and from control rats contained very low levels of these antibodies. Behavioral studies performed one year after the initial immunization revealed that the cholinergic PK immunized rats were impaired in spatial learning and memory tasks (Morris swim test and T-maze alternation) when compared to control rats and that the synaptosome-immunized rats showed no such deficit. In contrast, the three groups performed similarly in general activity, active avoidance and conditioned emotional response tests. Further experiments revealed that the cholinergic PK immunized rats displayed a significant deficit in short term memory. The association of antibodies to cholinergic neurons with cognitive deficits in this rat model suggests that such antibodies may be involved in the pathogenesis of AD.

Passive transfer of experimental autoimmune myasthenia gravis by monoclonal antibodies to the main immunogenic region of the acetylcholine receptor

Experimental autoimmune myasthenia gravis (EAMG) was passively transferred to rats by injecting monoclonal antibodies (mAbs) directed at the main immunogenic region (MIR) of the nicotinic acetylcholine receptor (AChR). The MIR is located on the extracellular part of the AChR alpha-subunit. All four mAbs directed at the MIR which were tested were very efficient in inducing EAMG: within 2 days the rats became moribund or very weak and their muscle AChR content decreased to about 50% of normal. These mAbs are of two different IgG subclasses (IgG1 and IgG2a) and derived from rats immunized with AChR from either fish electric organs or mammalian muscles. One mAb directed at the extracellular side of the beta-subunit did not cause AChR loss or induce symptoms of EAMG. mAbs to the cytoplasmic side were, as expected, ineffective.

Interactions of antinicotinic acetylcholine receptor antibodies with rat brain and muscle antigenic determinants

Studies were performed to determine whether antibodies prepared against nicotinic acetylcholine receptors (nAcChoR) from electric tissue are reactive toward nAcChoR-like antigenic determinants in rat brain. Reference experiments involved the use of Torpedo electroplax and rat innervated muscle as tissue controls and an anti-alpha-bungarotoxin antiserum as a probe for curaremimetic neurotoxin binding sites. As evinced by their ability to inhibit immunoprecipitation of Torpedo nAcChoR, brain or muscle membranes specifically interact with polyclonal antisera raised against Electrophorus electroplax nAcChoR. When the extent of polyclonal anti-nAcChoR antibody binding to muscle membranes is measured by protein A binding protocols, receptor-like antigenic determinants and toxin binding sites are found to be present in approximately equal quantities. In contrast, nAcChoR-like antigenic determinants on rat brain membranes are present at concentrations in excess of those of toxin binding sites. The results are consistent with the earlier observation that some antibodies prepared against nAcChoR from peripheral tissues recognize rat brain high-affinity alpha-bungarotoxin binding sites. The results also suggest the existence of nAcChoR-like entities in brain that do not bind toxin with a high affinity.

Ultrastructural study of neuromuscular junctions in experimental autoimmune myasthenia gravis (EAMG) in rabbits

Experimental autoimmune myasthenia gravis (EAMG) was produced in rabbits by the injection of acetylcholine receptor (AChR) protein from electric organ of Narkacion tokyonis with complete Freund's adjuvant, and the ultrastructural alterations of the neuromuscular junctions were studied. A lesion comparable to human myasthenia gravis could be observed in these animals. In acute EAMG, which showed a rapidly progressive severe paralysis 19 to 24 days after the first inoculation, distinct degeneration of the postsynaptic membrane was observed. Sometimes an irregular gap was found between the nerve terminal and postsynaptic sarcoplasm. In chronic EAMG with mild and prolonged muscle weakness, which appeared 23 to 54 days after the first inoculation, poorly developed junctional folds with little degenerative change were seen. By a morphometric analysis, some of the changes were detected even in a subclinical EAMG. In the presynaptic region, there was no ultrastructural alteration except that an increase of nerve terminal area was observed in chronic and subclinical EAMG. The pathogenesis of these alterations was discussed.

Monoclonal antibodies associated with sodium channel block nerve impulse and stain nodes of Ranvier

Monoclonal antibodies were generated against native eel electroplax sodium channels in their natural membrane. These antibodies block nerve conduction in rat central (optic) and peripheral (sciatic) nerve. The antibody binding to eel electroplax membrane fragments and to rat brain synaptosomes can be modulated by neurotoxins. Thus it implies that active sites of the sodium channels are immunogenic in their natural membrane. Unlike the antibodies described in the past, our antibodies recognize antigenic determinants which are associated with the physiological activity of the channel and have been conserved through evolution.

A synaptic vesicle antigen is restricted to the junctional region of the presynaptic plasma membrane

The plasma membrane of electric organ nerve terminals has two domains that can be distinguished by monoclonal antibodies. A library of 111 mouse monoclonal antibodies raised to nerve terminals from Torpedo californica contains 4 antibodies that bind specifically to the outside of intact synaptosomes. The distribution of the binding sites of these monoclonal antibodies on the outside of intact nerve terminals was examined by immunofluorescence and immunoelectron microscopy. The binding sites of 3 (tor23, 25, and 132) are distributed uniformly over nerve trunks and fine terminal branches. The binding site of the fourth (tor70) is restricted to synaptic junctional regions. This antibody, but not the other 3, recognizes a major component of synaptic vesicles, a proteoglycan associated with the inner surface of the vesicle membrane. The difference in the pattern of binding of these monoclonal antibodies suggests that the region of the plasma membrane containing active zones is antigenically distinguishable from other nerve terminal plasma membrane. We suggest that the antigen recognized by tor70 is externalized by exocytosis of synaptic vesicles while other plasma antigens take a different route to the surface. The unexpected observation that the vesicle antigen remains on the surface after exocytosis and is prevented from diffusion from the synaptic junctional region would be consistent with an interaction between the vesicle proteoglycan and elements of the synaptic cleft.

Production and characterization of a monoclonal antibody directed against the 43,000-dalton v1 polypeptide from Torpedo marmorata electric organ

Subsynaptic membrane fragments prepared from Torpedo marmorata electric organ contain, in addition to the acetylcholine receptor polypeptides, a major protein band of apparent molecular mass 43,000 daltons. On two-dimensional gels, this band yields three spots referred to as v1, v2, and v3. Monoclonal antibodies against the 43,000-dalton proteins were developed in CBA mice. One of them reacted exclusively with the v1 polypeptide but not with v2 and v3. Staining by the "immunogold" reaction followed by observation by electron microscopy showed that this antibody exclusively labeled the innervated membrane of T. marmorata electroplaque on its cytoplasmic face. Electroblots of one-dimensional gels of membrane preparations from 80-mm embryo electric organ were prepared. After reaction with the anti-v1 monoclonal antibody, a strongly stained 43,000-dalton band was revealed.

Selective interactions of electrolectins from eel electric organ and mouse thymus with mouse immature thymocytes

The pure electrolectin, a beta-D-galactoside binding lectin from the electric organ of the electric eel Electrophorus electricus, was found to agglutinate selectively a subpopulation of mouse thymocytes. This cell population could be separated from non-agglutinated cells by 1 g sedimentation over fetal calf serum. The agglutinated cells could be identified as immature thymocytes on the basis of the density of theta-antigen they bear on their surfaces, their mitotic activity and the absence of response to the mitogenic action of phytohemagglutinin. The immature mouse thymocytes were found to bind the endogenous mouse thymic lectin (MTL) a protein that displays the same saccharide specificity as the eel electrolectin and with which it cross-reacts immunologically. MTL is secreted by mouse thymic reticulocytes in tissue culture and its specific activity is markedly increased after depleting the thymus of its thymocytes. This finding is an indication of the possible localization of MTL in the thymic epithelium. These results are discussed in the light of our recent findings that the eel electrolectin has prophylactic and therapeutic actions on the experimental auto-immune myasthenia gravis in rabbits.

Use of a monoclonal antibody to purify the tetrodotoxin binding component from the electroplax of Electrophorus electricus

The tetrodotoxin binding component of the voltage-sensitive sodium channel from Electrophorus electricus electroplax was purified by using a monoclonal antibody. An impure preparation of tetrodotoxin binding component was mixed with the pure monoclonal antibody, and the immune complex so formed was isolated by affinity chromatography on a protein A-Sepharose column. Excess antibody was removed by ion-exchange chromatography. The purified material has a specific activity of over 1,800 pmol of [3H]tetrodotoxin bound per mg of protein. By assuming that the immune complex has a stoichiometry of 1:1, this specific activity then represents an actual specific activity of 3,000 pmol of [3H]tetrodotoxin bound per mg of eel electroplax protein, or 75% of the theoretical specific activity expected for a pure toxin binding component of Mr 250,000. The peptide composition of the purified material was simple with the predominant species present being of Mr approximately equal to 250,000. Minor components were also present with Mrs of approximately equal to 95,000, approximately equal to 44,000, and approximately equal to 23,000.

Isolation and characterization of a monoclonal antibody against the saxitoxin-binding component from the electric organ of the eel Electrophorus electricus

A monoclonal hybridoma cell line secreting antibody against the saxitoxin-binding component from the eel Electrophorus electricus has been isolated. The specificity of this monoclonal antibody was established by (i) its ability to immunoprecipitate bound [3H]saxitoxin from a detergent extract of electroplax membranes in a dose-dependent manner, (ii) the inability of unrelated monoclonal antibodies to immunoprecipitate the toxin-binding activity in a similar assay, and (iii) the ability of excess unlabeled tetrodotoxin to displace [3H]saxitoxin from the immunoprecipitated component. The antibody is of the subclass IgG1 and binds specifically to a polypeptide component of Mr approximately 250,000 on NaDodSO4/polyacrylamide gels. The antigenic determinant is associated with the same polypeptide component throughout the purification procedure, indicating that this component is not a result of artifactual aggregation or degradation during isolation. We conclude that the 250,000-dalton polypeptide is part of the saxitoxin binding/sodium channel protein in the native electroplax membrane.

Immunohistochemical localization of a synaptic-vesicle antigen in a cholinergic neuron under conditions of stimulation and rest

An antiserum against a specific component (a glycosamino glycan) of the cholinergic synaptic-vesicle of Torpedo marmorata has been used to investigate the localization of the component in the cell body, its movement within the electromotor axon and its fate within the nerve terminal upon electrical stimulation. After immunofluorescent staining, spots are observed throughout the cytoplasm of the lobe perikarya, although they are concentrated in the region of the axon hillock. Ligation of the electromotor nerves leading from the lobe to electric organ produces a proximal build-up of material which stains readily with the antivesicle antiserum, indicating that the vesicle antigen is transported from the cell body to the nerve terminal. A marked increase in indirect immunofluorescent staining of the electric organ is observed in the nerve ending upon electrical stimulation. We interpret this result as fusion of the vesicles with the presynaptic plasma membrane and exteriorization of the vesicle antigen to the extracellular space, thereby facilitating its staining. After recovery of the system the fluorescence declines, a result that is consistent with the reinternalization of the vesicle antigen into the core of reformed vesicles. The results support a mechanism whereby vesicles recycle within the nerve terminal and transmitter is released by exocytosis.

Presynaptic plasma membranes and synaptic vesicles of cholinergic nerve endings demonstrated by means of specific antisera

Antisera were raised to cholinergic presynaptic plasma membranes and synaptic vesicles isolated from the electric organ of Torpedo marmorata and tested by immunochemical and immunohistochemical methods. The antisera responded to many antigens not specific to nerve endings, but it was possible to eliminate these antibodies by means of simple absorption procedures with fractions containing the unwanted antigens. After absorption, staining of thin sections of electric organ by immunofluorescence was limited to the region of nerve endings in the tissue. The remaining antibodies responded in the case of the plasma membrane antisera predominantly to a 33,000 molecular-weight polypeptide and a chloroform/methanol-soluble antigen. In cross reactivity studies it was found that this antiserum not only stains cholinergic nerve endings in Torpedo but also those in mammalian tissue. The antigen responsible for the cross reactivity is restricted to the chloroform/methanol-soluble material. The vesicle antiserum labels cholinergic nerve endings in mammalian tissue as well; the relevant antigen in this case is different from the one described above and is likely to be a glycosaminoglycan. The antisera provide valuable markers for cholinergic nerve terminals. In addition, the vesicle antiserum may now be used to study axonal transport and the life cycle of this organelle in the cholinergic neurone.

The antigenic structure of the acetylcholine receptor from Torpedo californica

The immunological structure of the acetylcholine receptor (AChR) from the electric organ of Torpedo californica was studied using a large number of monoclonal antibodies which were initially selected for their abilities to bind to intact AChRs. The monoclonal antibodies were tested for their ability to bind to denatured AChR subunits labeled with 125I. Antibodies derived from rats immunized with individual denatured subunits or a mixture of subunits of Torpedo AChR reacted well in the assay. A much smaller proportion of antibodies derived from rats immunized with native Torpedo AChR or native AChR from Electrophorus electricus electric organ, bovine muscle, or human muscle reacted with denatured subunits of Torpedo AChR. Many monoclonal antibodies reacted with more than one subunit, but they always reacted best with the subunit used for immunization. Those monoclonal antibodies that bound to intact subunits were mapped more precisely by their ability to bind characteristic fragments of each subunit generated by proteolysis with Staphylococcal V8 protease. These fragments were analyzed by SDS polyacrylamide gel electrophoresis, and monoclonal antibodies that precipitated the same fragment pattern were placed in groups. By this method, we define a minimum of 28 determinants on Torpedo AChR.

An antiserum specific for cholinergic synaptic vesicles from electric organ

Rabbit antisera to highly purified synaptic vesicles from the electric organ of Narcine brasiliensis, an electric ray, reveal a unique population of synaptic vesicle antigens in addition to a population shared with other electric organ membranes. Synaptic vesicle antigens were detected by binding successively rabbit antivesicle serum and radioactive goat anti-rabbit serum. To remove antibodies directed against antigens common to synaptic vesicles and other electric organ fractions, the antivesicle serum was extensively preadsorbed against an electric organ membrane fraction that was essentially free of synaptic vesicles. The adsorbed serum retained 40% of its ability to bind to synaptic vesicles, suggesting that about half of the antigenic determinants are unique. Vesicle antigens were quantified with a radioimmunoassay (RIA) that utilized precipitation of antibody-antigen complexes with Staphylococcus aureus cells. By this assay, the vesicles, detected by their acetylcholine (ACh) content and the antigens detected by the RIA, have the same buoyant density after isopycnic centrifugation of crude membrane fractions on sucrose and glycerol density gradients. The ratio of ACh to antigenicity was constant across the vesicle peaks and was close to that observed for vesicles purified to homogeneity. Even though the vesicles make up only approximately 0.5% of the material in the original homogenate, the ratio of acetylcholine to vesicle antigenicity could still be measured and also was indistinguishable from that of pure vesicles. We conclude that synaptic vesicles contain unique antigenic determinants not present to any measurable extent in other fractions of the electric organ. Consequently, it is possible to raise a synaptic vesicle-specific antiserum that allows vesicles to be detected and quantified. These findings are consistent with earlier immunohistochemical observations of specific antibody binding to motor nerve terminals.

Antibodies to synaptic vesicles purified from Narcine electric organ bind a subclass of mammalian nerve terminals

Antibodies were raised in rabbits to synaptic vesicles purified to homogeneity from the electric organ of Narcine brasiliensis, a marine electric ray. These antibodies were shown by indirect immunofluorescence techniques to bind a wide variety of nerve terminals in the mammalian nervous system, both peripheral and central. The shared antigenic determinants are found in cholinergic terminals, including the neuromuscular junction, sympathetic ganglionic and parasympathetic postganglionic terminals, and in those synaptic areas of the hippocampus and cerebellum that stain with acetylcholinesterase. They are also found in some noncholinergic regions, including adrenergic sympathetic postganglionic terminals, the peptidergic terminals in the posterior pituitary, and adrenal chromaffin cells. They are, however, not found in many noncholinergic synapse-rich regions. Such regions include the molecular layer of the cerebellum and those laminae of the dentate gyrus that receive hippocampal associational and commissural input. We conclude that one or more of the relatively small number of antigenic determinants in pure electric fish synaptic vesicles have been conserved during evolution, and are found in some but not all nerve terminals of the mammalian nervous system. The pattern of antibody binding in the central nervous system suggests unexpected biochemical similarities between nerve terminals heretofore regarded as unrelated.

Specificities of antibodies to acetylcholine receptors

Antisera to acetylcholine receptor purified from the electric organs of Torpedo and Electrophorus were highly species specific, but showed limited cross-reaction with receptors from all mammalian species tested. Antisera to receptor purified from rat muscle cross-reacted extensively with receptor from the muscles of other mammals. Antibodies to receptor from Electrophorus cross-reacting with receptor from Torpedo were affinity purified. Subsequently these showed increased cross-reaction with receptor from mammalian muscle. Sera from patients with myasthenia gravis reacted best with receptor from human muscle, but such sera also cross-reacted with receptor from other mammals, especially squirrel monkeys. These sera cross-reacted slightly with receptor from Torpedo, but not detectably with receptor from Electrophorus,

[Autoimmune response following administration of a protein preparation from the caudate nuclei of cattle brains to rabbits]

Plasma membranes of bovine caudate nuclei were solubilized by means of Triton X-100. Detergent-extracted membrane proteins were separated by chromatography on DEAE-cellulose and the affinity adsorbent proposed for the isolation of nicotinic cholinergic receptor protein (N-ChR) from Torpedo electrical organ. Half of the rabbits immunized with purified protein preparation developed a syndrome of myasthenia type. This effect resembled the autoimmune response to N-ChR from fish electrical organs. It is assumed that the N-ChR present in the caudate nucleus has antigen determinants similar to N-ChRs of the electrical organs and skeletal muscles.

Experimental autoimmune myasthenia: A model of myasthenia gravis in rats and guinea pigs

Immunization of animals with acetylcholine receptor (AChR) protein from the electric organs of Electrophorus electricus and Torpedo californica induces an autoimmune response to the AChR of mammalian skeletal muscle. Rats and guinea pigs develop experimental autoimmune myasthenia gravis (EAMG) after a single inoculation with small quantities of AChR and adjuvant. The indicence and severity of disease appears to depend on the dose of AChR and stability of the emulsion. EAMG is strikingly similar to myasthenia gravis (MG) of man in its clinical picture and its electrophysiological abnormalities. The presence of antibodies to syngeneic rat muscle AChR in the serum of rats with EAMG documents the existence of autoimmunity in the experimental disease. A common immunopathogenesis is suggested for both EAMG and mg.

Neuromuscular transmission after immunization against acetylcholine receptors

Injection of acetylcholine receptors from the electric organ of Torpedo into rabbits or rats, produces antibodies which bind to acetylcholine receptors in the muscle membrane or in solution. Binding of antibody to the receptors results in diminished acetylcholine sensitivity of the muscle fibres, reduced amplitude of miniature end-plate potentials, block of neuromuscular transmission and a decrease in the ability of the receptors to bind a -bungarotoxin. Antibodies raised against acetylcholine receptors from Torpedo cross-react with acetylcholine receptors from rabbit, rat and frog muscle.