Anti-GM2 IgM antibodies: clinical correlates and reactivity with a human neuroblastoma cell line

IgM anti-GM2 antibodies in patients with multifocal motor neuropathy target Schwann cells and are associated with early onset

BACKGROUND

Multifocal motor neuropathy (MMN) is a rare, chronic immune-mediated polyneuropathy characterized by asymmetric distal limb weakness. An important feature of MMN is the presence of IgM antibodies against gangliosides, in particular GM1 and less often GM2. Antibodies against GM1 bind to motor neurons (MNs) and cause damage through complement activation. The involvement of Schwann cells (SCs), expressing GM1 and GM2, in the pathogenesis of MMN is unknown.

METHODS

Combining the data of our 2007 and 2015 combined cross-sectional and follow-up studies in Dutch patients with MMN, we evaluated the presence of IgM antibodies against GM1 and GM2 in serum from 124 patients with MMN and investigated their binding to SCs and complement-activating properties. We also assessed the relation of IgM binding and complement deposition with clinical characteristics.

RESULTS

Thirteen out of 124 patients (10%) had a positive ELISA titer for IgM anti-GM2. Age at onset of symptoms was significantly lower in MMN patients with anti-GM2 IgM. IgM binding to SCs correlated with IgM anti-GM2 titers. We found no correlation between IgM anti-GM2 titers and MN binding or with IgM anti-GM1 titers. IgM binding to SCs decreased upon pre-incubation of serum with soluble GM2, but not with soluble GM1. IgM anti-GM2 binding to SCs correlated with complement activation, as reflected by increased C3 fixation on SCs and C5a formation in the supernatant.

CONCLUSION

Circulating IgM anti-GM2 antibodies define a subgroup of patients with MMN that has an earlier onset of disease. These antibodies probably target SCs specifically and activate complement, similarly as IgM anti-GM1 on MNs. Our data indicate that complement activation by IgM antibodies bound to SCs and MNs underlies MMN pathology.

The cancer glycocode as a family of diagnostic biomarkers, exemplified by tumor-associated gangliosides

One unexploited family of cancer biomarkers comprise glycoproteins, carbohydrates, and glycolipids (the Tumor Glycocode).A class of glycolipid cancer biomarkers, the tumor-marker gangliosides (TMGs) are presented here as potential diagnostics for detecting cancer, especially at early stages, as the biological function of TMGs makes them etiological. We propose that a quantitative matrix of the Cancer Biomarker Glycocode and artificial intelligence-driven algorithms will expand the menu of validated cancer biomarkers as a step to resolve some of the challenges in cancer diagnosis, and yield a combination that can identify a specific cancer, in a tissue-agnostic manner especially at early stages, to enable early intervention. Diagnosis is critical to reducing cancer mortality but many cancers lack efficient and effective diagnostic tests, especially for early stage disease. Ideal diagnostic biomarkers are etiological, samples are preferably obtained via non-invasive methods (e.g. liquid biopsy of blood or urine), and are quantitated using assays that yield high diagnostic sensitivity and specificity for efficient diagnosis, prognosis, or predicting response to therapy. Validated biomarkers with these features are rare. While the advent of proteomics and genomics has led to the identification of a multitude of proteins and nucleic acid sequences as cancer biomarkers, relatively few have been approved for clinical use. The use of multiplex arrays and artificial intelligence-driven algorithms offer the option of combining data of known biomarkers; however, for most, the sensitivity and the specificity are below acceptable criteria, and clinical validation has proven difficult. One strategic solution to this problem is to expand the biomarker families beyond those currently exploited. One unexploited family of cancer biomarkers comprise glycoproteins, carbohydrates, and glycolipids (the Tumor Glycocode). Here, we focus on a family of glycolipid cancer biomarkers, the tumor-marker gangliosides (TMGs). We discuss the diagnostic potential of TMGs for detecting cancer, especially at early stages. We include prior studies from the literature to summarize findings for ganglioside quantification, expression, detection, and biological function and its role in various cancers. We highlight the examples of TMGs exhibiting ideal properties of cancer diagnostic biomarkers, and the application of GD2 and GD3 for diagnosis of early stage cancers with high sensitivity and specificity. We propose that a quantitative matrix of the Cancer Biomarker Glycocode and artificial intelligence-driven algorithms will expand the menu of validated cancer biomarkers as a step to resolve some of the challenges in cancer diagnosis, and yield a combination that can identify a specific cancer, in a tissue-agnostic manner especially at early stages, to enable early intervention.

Aiming for the Sweet Spot: Glyco-Immune Checkpoints and γδ T Cells in Targeted Immunotherapy

Though a healthy immune system is capable of recognizing and eliminating emergent cancerous cells, an established tumor is adept at escaping immune surveillance. Altered and tumor-specific expression of immunosuppressive cell surface carbohydrates, also termed the “tumor glycocode,” is a prominent mechanism by which tumors can escape anti-tumor immunity. Given their persistent and homogeneous expression, tumor-associated glycans are promising targets to be exploited as biomarkers and therapeutic targets. However, the exploitation of these glycans has been a challenge due to their low immunogenicity, immunosuppressive properties, and the inefficient presentation of glycolipids in a conventional major histocompatibility complex (MHC)-restricted manner. Despite this, a subset of T-cells expressing the gamma and delta chains of the T-cell receptor (γδ T cells) exist with a capacity for MHC-unrestricted antigen recognition and potent inherent anti-tumor properties. In this review, we discuss the role of tumor-associated glycans in anti-tumor immunity, with an emphasis on the potential of γδ T cells to target the tumor glycocode. Understanding the many facets of this interaction holds the potential to unlock new ways to use both tumor-associated glycans and γδ T cells in novel therapeutic interventions.

Sensitivity and predictive value of anti-GM1/galactocerebroside IgM antibodies in multifocal motor neuropathy

BACKGROUND

Increased titres of serum IgM antibodies to GM1 ganglioside are often associated with multifocal motor neuropathy (MMN). Testing for IgM antibodies to other antigens including GM2, the mixture of GM1 and galactocerebroside (GM1/GalC) and the disulfated heparin disaccharide NS6S were reported to increase the sensitivity of antibody testing in MMN even if it is unclear whether the specificity and positive (PPV) or negative predictive value (NPV) for MMN were also affected.

METHODS

We measured IgM antibodies to GM1, GM2, galactocerebroside, GM1/GalC and NS6S in 40 consecutive patients with MMN and 142 controls with other neuropathies or related diseases and compared their sensitivity, specificity and PPV for MMN.

RESULTS

With the only exception of anti-GM2 and, partially, anti-NS6S antibodies, IgM antibodies to the antigens tested were more frequent in MMN than in controls. Increased titres of anti-GM1 IgM were found in 48% of MMN patients with a specificity of 93% and PPV for MMN of 66%. Anti-GM1/GalC antibodies were present in all anti-GM1 positive MMN patients and in 11 additional patients (28%) with MMN raising the sensitivity of antibody testing to 75%. The specificity (85%) and PPV (59%) for MMN was, however, moderately reduced compared to anti-GM1 IgM, even if they rose with increasing anti-GM1/GalC titres. IgM antibodies to GM2, NS6S and galactocerebroside were found in 8%, 23% and 60% of MMN patients but had a low specificity and PPV for MMN.

CONCLUSIONS

Testing for anti-GM1/GalC IgM significantly increased the sensitivity of antibody testing in MMN compared to anti-GM1 alone (p=0.021) and may represent a preferred option for GM1 reactivity testing in MMN.

Antibody testing in peripheral nerve disorders

The identification of autoantibodies associated with dysimmune neuropathies was a major contribution to the characterization of peripheral nerve disorders, the understanding of their pathophysiology, and the clinical diagnosis of neuropathies. Antibodies directed to GM1, GQ1b, and disyalilated gangliosides, and anti-MAG antibodies are very useful in the diagnosis of acute or chronic motor or sensory-motor neuropathies with or without monoclonal IgM. Anti-onconeural anti-Hu and anti-CV2/CRMP antibodies allow when they are detected the diagnosis of paraneoplastic neuropathies. This chapter focuses on the description of these antibodies as diagnostic markers and on their immunopathogenesis. We give a background overview on the origin of these antibodies, their detection, and review those studies, which clearly show that these antibodies are capable of binding to the target tissues in peripheral nerve and thereby can exert a variety of pathophysiological effects. The corresponding electrophysiological and histological changes observed both in human and animal models are exemplified in order to get a better understanding of the immune mechanisms of these antibody-mediated neuropathies.

Multifocal motor neuropathy

Multifocal motor neuropathy (MMN) is a rare disorder in which the symptoms are caused by persistent conduction block lesions. The mononeuropathy multiplex progresses over time with increasing axonal loss. The cause of the conduction blocks and axonal loss are not completely understood but immune mechanisms are involved and response to intravenous immunoglobulin has been established. The importance of MMN goes beyond its clinical incidence as the increasing understanding of the pathogenesis of this disorder has implications for other peripheral nerve diseases and for our knowledge of peripheral nerve biology.

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.

Guillain-Barre syndrome: first description of a snake envenomation aetiology

BACKGROUND

Guillain-Barre syndrome (GBS) is considered as an acute, immune-mediated polyradiculoneuropathy with different clinical phenotypes arising after viral or bacterial infections, vaccination or surgery. However, in 40% of GBS patients the aetiology remains unknown. In this manuscript, we report the occurrence of GBS in a patient bitten by a snake (Vipera aspis) for which a cross-reaction was shown between GM2 ganglioside and glycosidic epitopes of venom proteins.

METHODS

The venom of the snake implied in the patient's envenomation was collected. Its composition was characterised by ELISA and SELDI-TOF MS. Cross-reactivities between venom proteins and GM2 gangliosides were identified by Western blot after immunoabsorption of patient's serum with increasing amounts of purified GM2. Enzymatic deglycosylation of the venom was performed to determine the specificity of the patient's serum cross-reaction.

FINDINGS

We proved the absence of neurotoxicity of the viper venom. The patient's serum presented specific cross-reactions with several glycosylated venom proteins. After deglycolysation of these proteins, the patient's serum cross-reactivity was abolished. Furthermore, we compared the immune response to venom proteins of sera from two groups of patients. The first group showed IgM reactivity against GM2 ganglioside associated with GBS, and cross-reacted with venom proteins. The second group presented an IgM reactivity against CMV, without neurological disorders, and reacted with neither venom proteins nor gangliosides.

INTERPRETATION

Our study proved the auto-immunological aetiology of GBS in our patient based on molecular mimicry mechanisms between venom proteins and GM2 ganglioside.

How useful are anti-neural IgM antibodies in the diagnosis of chronic immune-mediated neuropathies?

Antibodies against several neural antigens have been associated with different chronic immune-mediated neuropathies but their practical clinical relevance remains unclear. To determine the possible diagnostic usefulness of these antibodies we reviewed the clinical correlate of IgM antibodies to the myelin-associated glycoprotein (MAG), sulfatide, the gangliosides GM1, GM2, GD1a and GD1b in 539 consecutive patients examined for neuropathy or related diseases in our Neuropathy Clinics and tested for these antibodies in our laboratory since 1985. 302 patients (56%) had an established diagnosis of definite or possible chronic immune-mediated neuropathy while 237 had a neuropathy of non-immune-mediated origin or of unknown aetiology or a closely related disease. Antibodies to one or more antigen were more frequent (chi(2)=63.32; p<0.00001) in patients with chronic immune-mediated neuropathy (37.7%) than with other neuropathy or related diseases (7.2%) and their presence was associated in 87% of the patients with an immune-mediated neuropathy, incrementing by 31% the probability of having this form. Testing for MAG permitted to identify 24.8% of patients with an immune-mediated neuropathy, GM1 an additional 9.9%, while GM2, GD1b, GD1a and sulfatide altogether an additional 3% of the patients. Concerning clinical correlations, all 75 patients with anti-MAG IgM had neuropathy and IgM monoclonal gammopathy (PN+IgM) with a positive predictive value for this neuropathy of 100%. A similarly high predictive value for neuropathy (91.4%) was observed among 269 patients with IgM monoclonal gammopathy including 103 patients without neuropathy. Anti-sulfatide IgM, though rare, were also significantly and constantly associated with PN+IgM and permitted to identify few patients not bearing anti-MAG IgM. Anti-GM1 IgM were significantly associated with multifocal motor neuropathy (MMN) (29.2%) but where also found in a few patients with other immune or non-immune neuropathies or related diseases with a positive predictive value for MMN of 25.5%. Anti-GM2 IgM were also significantly associated with MMN and increased the sensitivity (36.2%) for MMN obtained with anti-GM1 IgM only, without affecting its specificity and positive predictive value. Anti-GD1a, GD1b, though not significantly more frequent in patients with immune-mediated neuropathy, were associated in 80 to 100% of patients with these neuropathies. In conclusion anti-neural IgM antibodies may help in identifying patients with a chronic immune-mediated neuropathy, even if only anti-MAG and anti-sulfatide IgM appear to be strictly associated with a definite clinical syndrome.

Multifocal motor neuropathy: current concepts and controversies

Multifocal motor neuropathy (MMN) is now a well-defined purely motor multineuropathy characterized by the presence of multifocal partial motor conduction blocks (CB), frequent association with anti-GM1 IgM antibodies, and usually a good response to high-dose intravenous immunoglobulin (IVIg) therapy. However, several issues remain to be clarified in the diagnosis, pathogenesis, and therapy of this condition including its nosological position and its relation to other chronic dysimmune neuropathies; the degree of CB necessary for the diagnosis of MMN; the existence of an axonal form of MMN; the pathophysiological basis of CB; the pathogenetic role of antiganglioside antibodies; the mechanism of action of IVIg treatments in MMN and the most effective regimen; and the treatment to be used in unresponsive patients. These issues are addressed in this review of the main clinical, electrophysiological, immunological, and therapeutic features of this neuropathy.

Neuropathies motrices multifocales avec blocs de conduction persistants : 18 ans après

Multifocal motor neuropathy with persistent conduction blocks was firstly reported in 1986 and outlined from the group of purely motor diseases of the peripheral nervous system. The main criterion is the presence of conduction blocks located only on the motor nerves; additionally 30 percent of patients have IgM subclass serum antibodies directed against GM1 ganglioside. The clinical picture is a multifocal, asymmetrical, neuropathy, starting and predominant in the upper limbs, occurring in males aged 50 years and more, and having a progressive course. There is no biological sign besides elevated anti-GM1 antibodies. CSF analysis discloses mild increased protein count. The course is unpredictable, the neuropathy may be strictly limited to one or two motor nerves, or spread to other motor nerves in the four limbs. There is no involvement of the sensory and the cranial nerves, no involvement of the autonomic and the central nervous system. The pathophysiology is unknown, animal models do not allow to confirm the role of humoral immunity, and the role of anti-GM1 antibodies is controversial. Randomized controlled trials have assessed the efficacy of intravenous immunoglobulins which dramatically improve strength in 70-80 percent of patients in the short term, but remain unable to prevent motor deterioration in most patients, together with the occurrence of new conduction blocks. Corticosteroids and plasma exchanges do not improve the patients and may be followed by transient worsening. Long-term efficacy of immunosuppressive agents is not known.

Multifocal motor neuropathy

Multifocal motor neuropathy (MMN) is a recently identified peripheral nerve disorder characterized by progressive, predominantly distal, asymmetric limb weakness mostly affecting upper limbs, minimal or no sensory impairment, and by the presence on nerve conduction studies of multifocal persistent partial conduction blocks on motor but not sensory nerves. The etiopathogenesis of MMN is not known, but there is some evidence, based mostly on the clinical improvement after immunological therapies, that the disease has an immunological basis. Antibodies, mostly IgM, to the gangliosides GM1, and though less frequently, GM2 and GD1a, are frequently detected in patients' sera, helping in the diagnosis of this disease. Even if there is some experimental evidence that these antibodies may be pathogenic in vitro, their role in the neuropathy remains to be established. Patients with MMN do not usually respond to steroids or plasma exchange, which may occasionally worsen the symptoms, while the efficacy of cyclophosphamide is limited by its relevant side effects. More than 80% of MMN patients rapidly improve with high dose intravenous immunoglobulin therapy (IVIg). The effect of this therapy is, however, transient and improvement has to be maintained with periodic infusions. A positive response to interferon-beta has been recently reported in a minority of patients, some of whom were resistant to IVIg. Even if many progresses have been made on the diagnosis and therapy of MMN, there are still several issues on the nosological position, etiopathogenesis and long-term treatment of this neuropathy that need to be clarified.

Anti-GM(2) IgM antibody-induced complement-mediated cytotoxicity in patients with dysimmune neuropathies

Anti-GM2 IgM antibodies have been reported in some patients with dysimmune neuropathy or lower motor neuron syndrome. To determine whether these antibodies can induce complement-dependent cytolysis we performed a cytotoxicity assay on neuroblastoma cells with sera from seven patients with demyelinating dysimmune neuropathies and high titers of anti-GM2 IgM. As controls we used sera from seven patients with other anti-neural reactivities, six with the same neuropathies but no anti-GM2 or other anti-neural reactivity and from eight normal subjects. Of the seven positive sera tested, six induced complement-mediated cytotoxicity, while none of the controls had any relevant effect on neuroblastoma cells. Preincubation of positive sera with purified GM2 removed cytotoxic activity. Affinity purified anti-GM2 IgM had the same cytotoxic anti-GM2 effect of whole serum while serum or complement alone did not have any effect. In four anti-GM2-positive patients the percentage of cell lysis correlated with anti-GM2 titers and with IgM staining of neuroblastoma cells while in two the cytotoxic effect was higher than expected from antibody titers. Complement-mediated cell lysis induced by anti-GM2 IgM antibodies may be a possible mechanism of neural damage in patients with dysimmune neuropathy and high titers of anti-GM2 IgM antibodies.

The role of antiglycolipid antibodies in peripheral neuropathies

The role of antiglycolipid antibodies in peripheral neuropathy continues to be defined in terms of clinical-serological associations and innovative experimental work establishing the role of these antibodies in pathogenesis. The present review focuses on the major developments in this field over the past 12 months.

Peripheral neuropathy associated with anti-GM2 ganglioside antibodies: clinical and immunopathological studies

GM2 ganglioside is a potential peripheral nerve antigen for neuropathy-associated autoantibodies. However little data are available on their pathogenic effects, if any. In this study we have screened both neuropathy-associated and control sera for anti-GM2 antibodies and subsequently used high titre sera for immunohistological and complement mediated cytotoxicity studies. We identified abnormally elevated anti-GM2 antisera in the normal population, as well as in patients with peripheral neuropathies and other neurological diseases. GM2 antibodies were either mono-reactive, cross-reactive with GM1a, or cross-reactive with GalNAc-GM1b and/or GalNAc-GD1a. All GM2 antisera from neuropathy subjects and normal controls bound to, and were capable of complement-mediated lysis of the NSC-34 cell line which expresses high levels of membrane-associated GM2. However, in immunohistological studies on human and rodent peripheral nervous system tissues, no specific binding was seen with GM2 antisera, either cross-reactive with GalNAc-GM1b and GalNAc-GDla, or with GM1a. These data indicate that although GM2 antisera can lyse neural membranes containing GM2, this antigen(s) is not detectable by standard immunohistological techniques in human or rodent peripheral nerve. This raises doubts about their pathophysiological significance in human autoimmune neuropathy.

Anti-sulfatide IgM antibodies in peripheral neuropathy

Anti-sulfatide IgM antibodies have been recently associated with neuropathy but the clinical and electrophysiological correlations of this reactivity remains unclear. We reviewed the clinical and electrophysiological features of patients with high anti-sulfatide titers detected in our laboratory from 1991 to 1998. Of the 564 patients with different neurological diagnosis tested by enzyme-linked immunosorbent assay (ELISA), 11 had high anti-sulfatide IgM titers (>1/8000), 26 had titers of 1/8000 while 78 had titers of 1/4000. All patients with high anti-sulfatide IgM titers had a chronic, dysimmune, mostly sensorimotor neuropathy that in seven was associated with IgM monoclonal gammopathy. In most of these patients electrophysiological and morphological studies were consistent with a predominantly demyelinating neuropathy frequently associated with prominent axonal loss. Antibody titers of 1/8000, though always associated with neuropathy, did not correlate with a particular form or cause of neuropathy, while lower titers were equally distributed in patients with different neurological disorders. Our study indicate that high anti-sulfatide IgM titers (>1/8000) are highly predictive for a chronic, dysimmune, mostly demyelinating neuropathy often associated with IgM monoclonal gammopathy, and may therefore have potential diagnostic relevance.

Autoantibodies associated with peripheral neuropathy

High titers of serum antibodies to neural antigens occur in several forms of neuropathy. These include neuropathies associated with monoclonal gammopathy, inflammatory polyneuropathies, and paraneoplastic neuropathies. The antibodies frequently react with glycosylated cell surface molecules, including glycolipids, glycoproteins, and glycosaminoglycans, but antibodies to intracellular proteins have also been described. There are several correlations between antibody specificity and clinical symptoms, such as anti-MAG antibodies with demyelinating sensory or sensorimotor neuropathy, anti-GM1 ganglioside antibodies with motor nerve disorders, antibodies to gangliosides containing disialosyl moieties with sensory ataxic neuropathy and Miller-Fisher syndrome, and antibodies to the neuronal nuclear Hu antigens with paraneoplastic sensory neuronopathy. These correlations suggest that the neuropathies may be caused by the antibodies, but evidence for a causal relationship is stronger in some examples than others. In this review, we discuss the origins of the antibodies, evidence for and against their involvement in pathogenic mechanisms, and the implications of these findings for therapy.