Anti-MAG IgM antibodies in patients with neuropathy and IgM M proteins: detection by ELISA

A novel cell-based immunofluorescence assay for the detection of autoantibodies to myelin-associated glycoprotein

Peripheral neuropathy with antibodies to myelin-associated glycoprotein (MAG) is an autoimmune demyelinating disorder of the peripheral nervous system caused by pathogenic IgM recognizing the human natural killer-1 glycoepitope expressed on MAG. This study aimed to analyze the performance of a new indirect immunofluorescence cell-based assay (CBA, EUROIMMUN) for the detection of anti-MAG IgM. Antibody reactivity was determined in sera from 95 patients with clinical and neurophysiological evidence of anti-MAG-associated neuropathy and in control samples from 55 patients with other forms of peripheral neuropathy. Compared to the results of the gold standard method (ELISA, Bühlmann) and using samples at a dilution of 1:100, the CBA had a sensitivity of 98.9% and a specificity of 100% (PPV 100%, NPV 98.2%). In conclusion, the CBA allows the detection of antibodies to MAG using an easy and standardized technique, and it presents a sensitive and specific alternative to the more time-consuming ELISA. Larger studies are needed to address anti-MAG titer monitoring in parallel with clinical activity.

Antibody testing in neuropathy associated with anti-Myelin-Associated Glycoprotein antibodies: where we are after 40 years

PURPOSE OF REVIEW

The diagnosis of Myelin-Associated Glycoprotein (MAG) neuropathy is based on the presence of elevated titers of IgM anti-MAG antibodies, which are typically associated with IgM monoclonal gammopathy, and a slowly progressive, distal demyelinating phenotype. The condition, however, can be under or over diagnosed in patients with mildly elevated antibody titers, absent monoclonal gammopathy, or an atypical presentation. The purpose of this paper is to examine recent advances in our understanding of the currently available anti-MAG antibody assays, their reliability, and their use in deciding treatment or monitoring the response to therapy.

RECENT FINDINGS

Higher titers of anti-MAG antibodies are more likely to be associated with the typical MAG phenotype or response to therapy. Mildly elevated antibody levels can occur in patients with chronic inflammatory demyelinating polyneuropathy. Testing for cross-reactivity with HNK1 can add to the specificity of the antibody assays. Patients with MAG neuropathy can present with an atypical phenotype and in the absence of a detectable monoclonal gammopathy.

SUMMARY

Assays for anti-MAG antibodies by Enzyme-Linked Immunosorbent Assay can be improved by testing for antibody binding at multiple serum dilutions, the inclusion of antigen-negative microwells as internal controls for each sample, testing for cross-reactivity with HNK1, and formal validation. The diagnosis needs to be considered in patients with demyelinating neuropathy, even in the absence of a monoclonal gammopathy or typical phenotype. The change in antibody levels needs to be considered in evaluating the response to therapy with B-cell depleting agents.

Aberrant Expression of Nodal and Paranodal Molecules in Neuropathy Associated With IgM Monoclonal Gammopathy With Anti-Myelin-Associated Glycoprotein Antibodies

To clarify the pathogenesis of anti-myelin-associated glycoprotein (MAG) antibody neuropathy associated with IgM monoclonal gammopathy (anti-MAG neuropathy), sural nerve biopsy specimens from 15 patients were investigated. Sodium channels, potassium channels, contactin-associated protein 1 (Caspr1), contactin 1, and neurofascin were evaluated by immunofluorescence in teased-fiber preparations. Immunoreactivity to the pan-sodium channel in both anti-MAG neuropathy patients and in normal controls was concentrated at the node of Ranvier unless there was demyelination, which was defined as the widening of the node of Ranvier. However, this immunoreactivity became weak or disappeared as demyelination progressed. In contrast, KCNQ2 immunostaining was nearly absent even in the absence of demyelination. The lengths of Caspr1, contactin 1, and pan-neurofascin immunostaining sites at the paranode were significantly increased compared with those of normal controls despite the absence of demyelination. The length of paranodal neurofascin staining correlated with the anti-MAG antibody titer, nerve conduction indices, the frequency of de/remyelination in teased-fiber preparations, and the frequency of widely spaced myelin (p < 0.05, p < 0.05, p < 0.01, and <0.05, respectively). These findings suggest that nodal and paranodal molecular alterations occur in early stages preceding the morphological changes associated with demyelination in anti-MAG neuropathy.

Diagnosis and treatment of chronic acquired demyelinating polyneuropathies

Chronic neuropathies are operationally classified as primarily demyelinating or axonal, on the basis of electrodiagnostic or pathological criteria. Demyelinating neuropathies are further classified as hereditary or acquired-this distinction is important, because the acquired neuropathies are immune-mediated and, thus, amenable to treatment. The acquired chronic demyelinating neuropathies include chronic inflammatory demyelinating polyneuropathy (CIDP), neuropathy associated with monoclonal IgM antibodies to myelin-associated glycoprotein (MAG; anti-MAG neuropathy), multifocal motor neuropathy (MMN), and POEMS syndrome. They have characteristic--though overlapping--clinical presentations, are mediated by distinct immune mechanisms, and respond to different therapies. CIDP is the default diagnosis if the neuropathy is demyelinating and no other cause is found. Anti-MAG neuropathy is diagnosed on the basis of the presence of anti-MAG antibodies, MMN is characterized by multifocal weakness and motor conduction blocks, and POEMS syndrome is associated with IgG or IgA λ-type monoclonal gammopathy and osteosclerotic myeloma. The correct diagnosis, however, can be difficult to make in patients with atypical or overlapping presentations, or nondefinitive laboratory studies. First-line treatments include intravenous immunoglobulin (IVIg), corticosteroids or plasmapheresis for CIDP; IVIg for MMN; rituximab for anti-MAG neuropathy; and irradiation or chemotherapy for POEMS syndrome. A correct diagnosis is required for choosing the appropriate treatment, with the aim of preventing progressive neuropathy.

Neuropathy and monoclonal gammopathy

The association of neuropathy with monoclonal gammopathy has been known for several years, even if the clinical and pathogenetic relevance of this association is not completely defined. This is not a marginal problem since monoclonal gammopathy is present in 1-3% of the population above 50 years in whom it is often asymptomatic, and in at least 8% of patients is associated with a symptomatic neuropathy, representing one of the leading causes of neuropathy in aged people. Monoclonal gammopathy may result from malignant lymphoproliferative diseases including multiple myeloma or solitary plasmocytoma, Waldenström's macroglobulinemia (WM), other IgM-secreting lymphoma or chronic lymphocytic leukemia, and primary systemic amyloidosis (AL). In most instances it is not associated with any of these disorders and is defined monoclonal gammopathy of undetermined significance (MGUS) for its possible, though infrequent, evolution into malignant forms. Several data support the pathogenetic role of the monoclonal gammopathy in the neuropathy particularly when of IgM isotype where IgM reactivity to several neural antigens has been reported. Increased levels of VEGF have been implicated in POEMS syndrome. However, there are as yet no defined therapies for these neuropathies, as their efficacy has not been confirmed in randomized trials.

Paraproteinemic neuropathies

The occurrence of a peripheral neuropathy (PN) in association with a monoclonal gammopathy is quite common and suggests that monoclonal proteins may play a pathogenetic role in peripheral nervous system damage. In fact, paraproteinemic PN constitute an heterogeneous group of disorders related to various pathogenetic factors, and the histopathologic features in peripheral nerve biopsies differ from one condition to another. In several well defined disorders, the responsibility of the monoclonal component in the development of the PN has been evidenced. This is the case for most of the PN associated with an IgM monoclonal gammopathy, either a monoclonal gammopathy of undetermined significance (MGUS) or Waldenstrom's macroglobulinemia. The responsibility of the monoclonal protein in the occurrence of amyloid neuropathy related to multiple myeloma is also recognized. However, most IgG or IgA MGUS, as well as the monoclonal component in POEMS syndrome, have an uncertain causal relationship with the neuropathy. PN associated with monoclonal cryoglobulin (type 1) are occasional and differ from those associated with mixed cryoglobulins (types 2 or 3).

Anti-alpha- and beta-tubulin IgM antibodies in dysimmune neuropathies

An increased frequency of serum IgM antibodies to beta-tubulin has been found by ELISA in patients with chronic inflammatory demyelinating polyneuropathy (CIDP) and the Guillain-Barré syndrome (GBS). We used an immunoblot technique to compare the frequency, titer and specificity of anti-tubulin IgM antibodies in 207 patients with different neuropathies, 109 with other neurological disease (OND) and 110 non-neurological controls. High titers of serum anti-tubulin IgM antibodies (> 1:1600) were present in 2 patients with CIDP (10.5%), 1 with multifocal motor neuropathy (MMN) (11%), 1 with GBS (1.8%), two with IgM monoclonal gammopathy, one with (1.3%) and one without neuropathy (2.1%), and in two with OND (1.8%). Even if the relative binding to alpha- and beta-tubulin differed among positive patients, in all IgM bound to both tubulin subunits. All positive patients had a similarly intense IgM reactivity with tubulin by ELISA that showed high anti-tubulin IgM in 4 additional CIDP patients (total positive by ELISA 30%) and in 7 of 23 normal subjects (30%). Even if high anti-tubulin IgM were slightly more frequent by immunoblot in chronic dysimmune neuropathies than in other diseases, possibly reflecting a secondary response to neural damage during an ongoing immune response, their relatively low frequency in these diseases does not seem to justify their measurement for diagnostic application.

Axonal degeneration accompanied by conduction block induced by toxin mediated immune reactivity to GM1 ganglioside in rat nerves

Immune mechanisms have been implicated in the pathogenesis of motor neuropathy with conduction blocks and of acute axonal neuropathy, and GM1 ganglioside has been identified as a potential target antigen. In these experiments, the B subunit of cholera toxin (CT-B), which binds to GM1, was used to target an antibody response to GM1 in peripheral nerve. CT-B was injected into the sciatic nerves of rats, in which anti-CT antibodies were previously induced by immunization, so that the circulating anti-CT-B antibodies bound to the CT-B-GM1 complex in the nerve. Electrophysiological studies revealed the presence of conduction block, and in pathological studies there was axonal degeneration with little demyelination. Control animals, in which keyhole limpet hemocyanin was substituted for CT, did not develop conduction block or axonal degeneration. These studies indicate that antibodies directed at GM1 sites in peripheral nerve could cause an axonal neuropathy with conduction block.

Serum anti-GM1 and anti-GD1a antibodies in patients with motor neuron disease

Using an enzyme-linked immunosorbent assay (ELISA) sera from 100 individuals, 20 with motor neuron disease (MND), 25 with peripheral neuropathy (PN), 15 with degenerative dementia and 40 controls, were examined in order to detect serum IgM and IgG anti-GM1 and anti-GD1a antibodies. Patients with MND showed statistically significant higher levels of IgM anti-GM1 antibody compared to the control group. Three patients with peripheral neuropathy had very high levels of anti-GM1 and anti-GD1a antibodies. Antibody levels in patients with degenerative dementia showed no difference compared to the controls. These results suggest that a further inquiry into the role of serum anti-GM1 and anti-GD1a activity in motor neuron disease and peripheral neuropathy is necessary.

Castleman's disease in POEMS syndrome with elevated interleukin-6

POEMS syndrome is a rare multisystem affliction known for its signs, from which it also takes its acronym name "peripheral neuropathy, organomegaly, endocrinopathy, monoclonal (M) protein, and skin lesions." Our study chronicles the course of this syndrome in a young woman with Castleman's disease (angiofollicular lymph node hyperplasia). Cerebrospinal fluid (CSF) and serum interleukin-6 (IL-6) levels were abnormally elevated at various times during a 9-month period. The authors conclude that the plasma cell dyscrasia associated with the POEMS syndrome of this patient was Castleman's disease. Elevation of serum IL-6 levels might contribute to the pathogenesis of the POEMS syndrome.

Antibodies to peripheral nerve myelin may occur without clinical neuropathy in healthy persons

To study the role of autoantibodies against peripheral nerve myelin (PNM), sera from 255 healthy blood donors were investigated by enzyme-linked immunosorbent assay (ELISA), and persons with anti-PNM antibodies were further studied clinically and by neurography, 25 blood donors (10%) had anti-PNM antibodies of IgM, IgG or IgA isotype. The 12 blood donors with anti-PNM antibodies of IgM isotype showed only slightly decreased nerve conduction velocities compared to 12 blood donors without anti-PNM antibodies. Two blood donors with anti-PNM antibodies of IgM and IgG isotype respectively showed a clinical, previously undiagnosed polyneuropathy (PN), verified by neurography. However, also one blood donor without anti-PNM antibodies had a clinical and neurography-verified PN. We conclude that antibodies against PNM may occur in healthy persons without evidence of a clinical or subclinical PN.

Polyneuropathy associated with IgM monoclonal gammopathy. Immunological and pathological study in 31 patients

Quantitative, immunopathological, light and electron microscopic studies of superficial peroneal nerve biopsies from 31 patients with IgM monoclonal gammopathy were carried out. Six patients had Waldenström's macroglobulinemia and 25 had IgM monoclonal gammopathy of undetermined significance. Serum samples from 28 of these patients were assayed for anti-myelin-associated glycoprotein (anti-MAG) activity. Anti-MAG activity was found in 25 of the samples. There was a relationship between the widening of some myelin lamellae observed on ultrastructural examination and the serum anti-MAG activity (23 cases). Immunopathological examination showed IgM binding to myelin sheaths in 17 cases.

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.

AAEE case report #17: Peripheral neuropathy in monoclonal gammopathy of undetermined significance

Monoclonal gammopathy of undetermined significance (MGUS) is the most common paraproteinemia associated with polyneuropathy. Although the clinical and electrodiagnostic manifestations most resemble those of chronic inflammatory demyelinating polyneuropathy, some patients manifest a pure sensory neuropathy or neuronopathy. The M protein is usually IgM, and its concentration in serum is low. Nerve pathology from patients with demyelinating disease shows a reduction of large myelinated fibers and segmental demyelination with remyelination. In some cases, the M protein possesses antibody activity against components of the myelin sheath or axon. These neuropathies may respond to treatment with steroids, immunosuppressant agents, and plasma exchange.

Treatment of patients with neuropathy and anti-MAG IgM M-proteins

Five patients with neuropathy and IgM M-proteins that reacted with myelin-associated glycoprotein (MAG) were treated for 10 to 20 months with cytostatic agents. In 2 patients, a decrease in serum M-protein and in anti-MAG IgM levels coincided with a progressive improvement of neuropathy. No clinical improvement and no decrease of anti-MAG IgM were observed in the other patients. The close relationship between the decrease of anti-MAG M-proteins and clinical improvement in these patients supports the pathogenetic role of the M-protein in the neuropathy.

Antibodies to sulfated glucuronic acid containing glycosphingolipids in neuropathy associated with anti-MAG antibodies and in normal subjects

Serum of patients with neuropathy and IgM monoclonal antibodies (M-proteins) that bind to the myelin-associated glycoprotein (MAG) were tested for binding to the major cross-reactive sulfated glucuronic acid containing glycosphingolipid, sulfated glucuronic acid paragloboside (SGPG). IgM binding to the glycolipid was detectable at serum dilutions of 1:10,000 and reactivity was greatest at 4 degrees C. Low titers of IgM binding to the glycolipid were also detected in sera from normal subjects and from patients with neurologic or rheumatologic diseases without serum M-proteins. Binding activity was present in 25% of the sera tested, and titers ranged between 1:25 and 1:400. One patient with peripheral neuropathy, however, had a measurable titer of 1:12,800 in the absence of monoclonal gammopathy. The study indicates that cold reacting anti-SGPG IgM antibodies are frequent constituents of the normal human antibody repertoire, and that monoclonal or polyclonal expansion of B cells that secrete these antibodies, is associated with peripheral neuropathy.

Subcellular localization of sulfated glucuronic acid-containing glycolipids reacting with anti-myelin-associated glycoprotein antibody

Peripheral nerve glycolipids, with which anti-myelin-associated glycoprotein (MAG) antibodies from patients with demyelinating neuropathy and plasma cell dyscrasia cross-react, proved to be novel glycosphingolipids containing a sulfated glucuronyl residue. Consequently, there has been much interest in the immunological role that these sulfated glucuronyl-glycosphingolipids (SGGLs) may play in the pathogenesis of this disorder. For the determination of the distribution of these glycolipids in various nervous tissues and, thereby, the elucidation of their pathogenicity, a quantitative immunostaining-TLC method for their detection has been devised. Using this method, we demonstrated that these glycolipids were distributed in greatly different amounts in the peripheral nerves from human, bovine, chicken, rat, and rabbit. Subcellular localization studies of bovine peripheral nerve also demonstrated that they were enriched in the axolemma-enriched fraction and present in glial-related membranes in lower concentrations. In addition, these glycolipids were present in bovine dura mater and transformed rat Schwann cells. These biochemical results suggest that not only myelin but also axons could be involved as targets of the anti-MAG antibody in macroglobulinemia neuropathy, and it may also be necessary to examine anti-SGGL activity in patients with axonal neuropathy associated with plasma cell dyscrasia.

Generation of human B-cell hybridomas secreting monoclonal anti-myelin-associated glycoprotein antibodies from a patient with neuropathy

Human hybridomas that secrete monoclonal IgM anti-myelin-associated glycoprotein antibodies were generated by fusion with cells from a patient with peripheral neuropathy and IgM monoclonal gammopathy. Karyotypic analysis of the hybridoma cells revealed no chromosomal abnormalities. The cells were positive for cell-surface idiotype HLA-DR and the plasma cell antigen PCA-1, and negative for the B-cell determinant B4 and for Leu-1, which has been postulated to distinguish a subpopulation of B cells that secrete IgM with autoantibody activity.

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.

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.

Benign monoclonal IgAK gammopathy associated with polyneuropathy and dysautonomia

The first case of benign IgAK monoclonal gammopathy associated with peripheral neuropathy is described. Dysautonomia is an unusual, yet prominent, manifestation of neuropathy in this patient. Electrodiagnostic testing and nerve biopsy were compatible with demyelination and axonal loss. Myelin sheath, perineural, and endoneural interstitial tissue fixation of anti-IgA and anti-kappa light chains was demonstrated by direct immunofluorescence microscopy. Absorption studies utilizing human peripheral nerve myelin resulted in complete removal of the paraprotein band. Analytic procedures with myelin-associated glycoprotein and gangliosides, however, were negative. Based on these findings, an alternative etiology for this neuropathy is hypothesized.

Peripheral neuropathy and monoclonal IgM with antibody activity against peripheral nerve myelin; effect of plasma exchange

Serum IgM antibodies directed against peripheral nerve myelin were demonstrated using enzyme-linked immunosorbent assay, mixed haemagglutination and indirect immunofluorescence in 3 patients with chronic polyneuropathy and monoclonal serum IgM. Isoelectric focusing followed by antigen immunofixation and autoradiography showed that the antimyelin antibodies co-migrated with the monoclonal IgM. Plasma exchange alone, without chemotherapy, proved beneficial in 2 patients. In one patient, plasma exchange was discontinued because of low IgG levels. Serum IgM and antimyelin antibodies decreased during plasma exchange and no increase beyond initial levels was noted after cessation of treatment.

Immunofluorescence study of patients with neuropathy and IgM M proteins

Immunofluorescence histochemistry was used to study the pathogenesis of polyneuropathy in patients with an IgM M protein. Seventeen patients had an M protein that reacted with myelin-associated glycoprotein (MAG), and their serum immunostained myelin sheaths of normal peripheral nerve of humans and certain other species. The staining was specific for the M protein idiotype and was abolished by prior absorption of serum with MAG. The sural nerve biopsy specimens from these 17 patients had pathological features of primary demyelination and deposits of IgM on the myelin sheaths. Sural nerve specimens of 2 patients with an M protein reactive with chondroitin sulfate showed axonal degeneration and diffuse deposits of IgM in the endoneurium. Serum of one of these patients immunostained connective tissue; the staining was specific for the M protein idiotype and was blocked by absorption of the serum with chondroitin sulfate. The antigenic specificity of the IgM M protein in another 9 patients with neuropathy is not known; however, sural nerve specimens obtained from some of the patients showed axonal degeneration and endoneurial deposits of IgM, and the serum IgM immunostained axons in some instances. The findings suggest that IgM M proteins may cause the neuropathy and that more than one autoantigen is involved.

Neuropathy and anti-myelin-associated glycoprotein IgM M proteins: T cell regulation of M protein secretion in vitro

In patients with plasma cell dyscrasia, individual clones of antibody-producing cells proliferate abnormally and secrete monoclonal antibodies or M proteins in excess. The cause of the monoclonal proliferation of lymphocytes and M protein secretion is unknown and it is not known whether the M protein-secreting B cells are autonomous or capable of responding to regulatory T cells. We carried out experiments using lymphocytes from a patient with neuropathy and plasma cell dyscrasia whose IgM M protein bound to the myelin-associated glycoprotein (MAG) to determine whether secretion of the M protein in vitro was responsive to T cell help or suppression. M protein secretion was measured by an enzyme-linked immunosorbent assay system for measuring anti-MAG IgM, and the number of M protein-secreting lymphocytes was enumerated by a reverse hemolytic plaque assay specific for the M protein idiotype. The patient's B cells were maximally stimulated by pokeweed mitogen-activated autologous OKT4+ T-helper cells and the helper effect was inhibited by OKT8+ suppressor/cytotoxic T cells. Low levels of M protein secretion in the absence of T cells were also observed and there was partial stimulation of M protein secretion by T cells in the absence of pokeweed mitogen.

Antibody to glycolipid in a patient with IgM paraproteinemia and polyradiculoneuropathy

Serum from a patient with IgM paraproteinemia and polyradiculoneuropathy, diagnosed as malignant lymphoma reacted specifically with a lipid component in a crude ganglioside fraction isolated from human peripheral nerve, but did not react with myelin proteins including myelin-associated glycoprotein (MAG). The reactive glycolipid migrated between GM1 and GD1a gangliosides on TLC, and there was no distinct band corresponding to this glycolipid on examination with resorcinol reagent. Antibody to glycolipid in this case may play a role in the pathogenesis of neuropathy.

Peripheral neuropathies associated with monoclonal proteins: a clinical review

Over the last decade, the increasing use of serum and urine protein electrophoretic screening of patients with idiopathic peripheral neuropathy has led to greater recognition of peripheral neuropathy syndromes that are associated with monoclonal proteins and plasma cell dycrasias. After careful evaluation, most of these patients have benign monoclonal gammopathy, followed in frequency by primary systemic amyloidosis and osteosclerotic myeloma, with occasional cases associated with osteolytic multiple myeloma, Waldenstrom's macroglobulinemia, gamma heavy chain disease, and other rare disorders. Several of these syndromes have distinctive presentations and are recognizable clinically, whereas others (especially multiple myeloma neuropathy) are diverse clinically and are not clearly distinguishable from other chronic neuropathies. The discovery of IgM-kappa monoclonal proteins directed at myelin antigens in some patients with benign monoclonal gammopathy and the delineation of the syndrome of neuropathy and multiorgan involvement in osteosclerotic myeloma are important developments which may shed light on the mechanism of the remote effects of malignancies on the nervous system.

The binding of human IgM paraprotein from cases of polyneuropathy associated with benign monoclonal gammopathy to specific neurons of the rodent brain

Human sera from patients with IgM paraproteinaemia were screened for IgM binding to frozen sections of the rat cerebellum by the indirect immunoperoxidase procedure. Out of 18 patients with a benign IgM gammopathy and associated demyelinating polyneuropathy (PPN), 17 showed binding to the surface of specific neurons, i.e. those of the deep cerebellar nuclei and the intermediate cell of Lugaro. Examination of other regions of the mouse brain suggests that the reactivity is restricted to cells of certain nuclei of the sensory-motor system. The use of F(ab)2 and monoclonal anti-idiotype antibodies demonstrate that the binding involves the antigen binding sites of the paraprotein. This reactivity indicates that some neurons have on their surface an antigen having an hapten in common with human myelin-associated glycoprotein (MAG) and the pi granules of human Schwann cells and furthermore is an additional serological characteristic of this group of patients. In addition 3 sera from the PPN group stained a particulate component in the cytoplasm of all medium-sized and large neurons. A similar staining was found with 7 out of 52 other unselected IgM paraproteinaemias.