Anti-MAG antibody and antibody complexes: detection by radioimmunoassay

Myelinated dorsal root ganglion cultures activate both the alternative and classical pathways of complement

We used rat myelinated dorsal root ganglion (MDRG) cultures to study antibody and complement-mediated mechanisms of peripheral demyelinating diseases. Heat inactivated serum from a patient (LT) with peripheral neuropathy and a monoclonal IgM reactive with myelin-associated glycoprotein (anti-MAG) and sulfated glucuronosyl glycolipids (anti-SGGL) was used as an antibody source. Incubation of whole human serum (WHS) or WHS and anti-SGGL with MDRGs resulted in reduction of classical and alternative pathway hemolytic activities and the development of abnormal myelin sheaths. Incubation of MDRG cultures with C2-deficient serum showed activation of the alternative complement pathway. Classical pathway hemolytic activity was reduced when Factor B-depleted serum was incubated with MDRG cultures. The rat MDRG culture system provides a good model system of a peripheral nerve and has therefore been used by several investigators to study antibody and complement-mediated demyelination associated with peripheral neuropathies. However, our studies indicate a high degree of complement activation and membrane disruption of cultures incubated with WHS.

Sensitization of Lewis rats with sulfoglucuronosyl paragloboside: electrophysiological and immunological studies of an animal model of peripheral neuropathy

Antibodies against sulfoglucuronosyl glycosphingolipids (SGGLs) are known to be present in sera of patients with chronic polyneuropathy associated with IgM paraproteinemia. We recently studied rats sensitized with sulfoglucuronosyl paragloboside (SGPG), a major SGGL species, emulsified with keyhold limpet hemocyanin and Freund's adjuvant. The titer of the IgM class antibodies against SGPG increased up to 1:1,600, while that of the IgG class increased up to 1:800 2 weeks after sensitization. The antibodies showed a high degree of antigenic specificity; no cross-reactivity with other brain glycolipids could be detected. They, however, reacted with human myelin-associated glycoprotein (MAG) by Western blot analysis, but not with rat MAG. These animal models showed minor but clear clinical signs of neuropathy, consisting of mild tail muscle tone loss and walking disabilities. Electrophysiological examination of the sciatic nerves revealed nerve conduction abnormalities which consisted of conduction block and mild decrease in conduction velocity. Thus, our results support the concept that anti-SGPG antibodies may play an important pathogenetic role in this type of chronic neuropathy.

Neuropathies associated with monoclonal gammopathies

Approximately 10% of patients with idiopathic peripheral neuropathy have an associated serum monoclonal gammopathy or M-protein. This represents six times the incidence of M-proteins found in the general population. In 5% of idiopathic peripheral neuropathy patients the M-protein is associated with an identifiable plasma cell dyscrasia. Sclerotic myeloma is particularly important to recognize because treatment may result in amelioration of the neuropathy and remission of the tumor. Patients with primary systemic amyloidosis often have preferential small fiber involvement with a dissociated sensory loss and autonomic dysfunction. The nerve root infiltration of lymphoproliferative disorders may simulate a polyradiculoneuropathy. In cases without an identifiable cause for the M-protein, referred to as monoclonal gammopathy of undetermined significance (MGUS), the pathophysiologic basis for the neuropathy is poorly defined in most cases. A role for M-proteins with antibody activity to myelin-associated glycoprotein is provocative. This review summarizes current knowledge of this important group of disorders.

Clinical, neurophysiological and immunological evidence of polyneuropathy in patients with monoclonal gammopathies

In this study we estimated the prevalence of polyneuropathy (PN) in patients with monoclonal gammopathies. 31 patients with monoclonal gammopathies (19 with monoclonal gammopathy of uncertain significance (MGUS), 10 with multiple myeloma (MM), and 2 with Waldenström's macroglobulinemia), were studied by clinical and neurophysiological examination, blood tests to exclude other causes of PN, ELISA assays to detect antibodies to peripheral nerve myelin (PNM), and antibodies to myelin associated glycoprotein (MAG). 11 of 31 patients (36%) had a clinical PN, 3 (10%) had a probable PN (signs but no symptoms), and 4 (13%) had a subclinical PN (only neurophysiological signs of PN). Thus, in total 18 patients (58%) had some form of PN, in contrast to an age-matched control group (n = 33) where only 2 persons (6%) had some form of PN; 1 had a probable PN and 1 had a subclinical PN. 3 patients had anti-PNM and anti-MAG antibodies of IgM isotype, all 3 patients showing a demyelinating PN. The remaining patients with PN had a mild or moderate distal PN. One patient had a myelopathy and 1 had amyotrophic lateral sclerosis (ALS). IgM isotype of the M-protein was associated with a high risk of clinical PN (5 out of 6 (83%)), in contrast to IgG (5 out of 18 (28%)) and IgA (1 out of 6 (17%)). We conclude that PN is a common finding in patients with monoclonal gammopathies, but only some of them are of the demyelinating type and associated with antibodies to PNM or MAG.

Seric immune complexes in multiple sclerosis do not contain MBP epitopes

Immune complexes from sera of MS patients, other neurological diseases, and healthy donors were precipitated using polyethyleneglycol and analyzed by sodium dodecylsulfate-polyacrylamide gel electrophoresis. Silver staining evidenced additional protein bands whose molecular weights were 14-16, 38, and 43 kDa. These IC proteins were present in most MS patients studied. To identify their nature, immunoblotting was performed with antihuman immunoglobulins A, M, G antibodies. No immunoreactivity was found below a molecular weight of 66 kDa on a nitrocellulose sheet having the transferred protein pattern of MS IC. Using purified human myelin, MS IC transferred to an immobilon sheet and antihuman myelin basic protein antibodies, an immunoreactivity was seen only on purified human MBP. The small proteins of 14-16 kDa and the others of 38, 43 kDa were not immunoreactive. Identification of the nature of these additional proteins in MS IC is in progress.

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.

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.

Identification and characterization of anti-conjugated azelaic acid antibodies in multiple sclerosis

Human sera from patients with multiple sclerosis (MS) were tested using an enzyme-linked immunosorbent assay (ELISA) method on well plates coated with various dicarboxylic acid (C4 to C10) protein conjugates. Specific immunological binding was found with an azelaic acid (AzeA, C9) conjugate. The antibody titer was higher in the sera from the patients in acute relapse than with the progressive form, and higher than that from sera of patients with other neurological diseases and healthy subjects. Modifications of coating concentrations and of antibody dilutions, and experiments with preadsorption enabled determination of binding specificity. Competition experiments with related conjugates demonstrated that the AzeA residue was 167 times better recognized by antibodies from MS patients in acute relapse than those from controls. The suberic and sebasic acid conjugates which only differ from the AzeA conjugate by one methylene group were less well-recognized by MS sera (11 and 47 times, respectively) than the conjugate AzeA-BSA.

Familial aggregation of multiple myeloma and central nervous system diseases

Degenerative central nervous system diseases such as Alzheimer's disease and lymphoreticular malignancies such as multiple myeloma occur with increased frequency with advancing age. Relatives of early-onset Alzheimer's disease patients may have an increased risk of lymphoreticular malignancies. This led us to evaluate the family history of central nervous system diseases in a case-control study of multiple myeloma. Thirteen of 439 multiple myeloma cases had one or more first-degree relatives with degenerative or demyelinating central nervous system disease. In comparison, there were nine "positive" family histories in 1,317 matched hospital controls (relative risk = 4.4, 95% confidence interval = 1.9-10.3). Relative risks for the component categories of Parkinson's disease, multiple sclerosis, and miscellaneous degenerative central nervous system diseases were 3.0, 4.0 and 11.9, respectively. Our findings suggest that the degenerative and demyelinating central nervous system diseases and the lymphoreticular malignancies may comprise an etiologically related group of "protean diseases." These diseases may have a shared genetic susceptibility, possibly an immunologic abnormality. The varied disease manifestation in family members suggests a second necessary etiologic step of a variable and possibly environmental nature.

Antibodies to myelin-associated glycoprotein (MAG) in the cerebrospinal fluid of multiple sclerosis patients

Cerebrospinal fluids (CSF) and sera from patients with multiple sclerosis (MS), other neurological diseases (ONDs) and healthy controls were tested for antibodies to myelin-associated glycoprotein (MAG) by several different assays. Using a very sensitive, solid-phase radioimmunoassay with radioiodinated protein A, a statistically significant elevation of anti-MAG antibodies was detected in MS CSFs in comparison to those from ONDs and healthy controls. The antibodies reacted with human MAG, but not with rat MAG, and appeared to be directed towards carbohydrate determinants in the glycoprotein. The CSFs from high IgG producers had significantly greater anti-MAG antibody levels than those from low IgG producers, even though the assays were done on CSF samples that had been normalized to the same IgG concentration. The elevated antibodies were not detected when the same samples were tested with a liquid-phase radioimmunoassay or an enzyme-linked immunosorbent assay, and the antibodies in the MS CSF also could not be detected by Western blotting. An elevated level of antibodies was not found in sera from MS patients by any of the assays, possibly because these samples gave higher and more variable background. The results suggest that there is a low level of humoral immunity to MAG in MS patients that can only be detected by the most sensitive assays. This weak immune response to MAG may be secondary to the demyelinating process, but could play a role in the progression of the disease.

Humoral factors in inflammatory disorders of the central and peripheral nervous system

The immune-mediated disorders of the central and peripheral nervous systems all involve humoral mechanisms in which immunoglobulin, complement and/or other mediators are implicated. The disorders can be characterized by pattern of disease activity, site of immunoglobulin synthesis, humoral mechanism of injury, and presence of one or more concurrent cellular mechanisms of injury. Control of the humoral responses is presumably T-cell dependent. While these disorders should be viewed as having both humoral and cellular components, the specific components of each disorder might predict the response to specific therapeutic approaches.

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.

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.