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

Evidence for the role of B cells and immunoglobulins in the pathogenesis of multiple sclerosis

The pathogenesis of multiple sclerosis (MS) remains elusive. Recent reports advocate greater involvement of B cells and immunoglobulins in the initiation and propagation of MS lesions at different stages of their ontogeny. The key role of B cells and immunoglobulins in pathogenesis was initially identified by studies in which patients whose fulminant attacks of demyelination did not respond to steroids experienced remarkable functional improvement following plasma exchange. The positive response to Rituximab in Phase II clinical trials of relapsing-remitting MS confirms the role of B cells. The critical question is how B cells contribute to MS. In this paper, we discuss both the deleterious and the beneficial roles of B cells and immunoglobulins in MS lesions. We provide alternative hypotheses to explain both damaging and protective antibody responses.

Distinct cytokine patterns associated with different forms of chronic dysimmune neuropathy

To better understand the presumed immune system dysregulation of chronic dysimmune neuropathy (CDN) patients, we designed a study to evaluate the levels of pro- and anti-inflammatory cytokines in the most common forms of CDN: chronic inflammatory demyelinating polyneuropathy (CIDP), and anti-myelin-associated glycoprotein (MAG)-related polyneuropathy (MAGnp). Sixteen patients fulfilled diagnostic criteria for CIDP, 14 were diagnosed with MAGnp, and 36 were classified as exhibiting "chronic idiopathic polyneuropathy" (CIP). Cytokine production in mitogen-stimulated peripheral blood mononuclear cells (PBMCs) was analyzed by flow cytometry. CIDP and MAGnp patients were compared with CIP patients, those with monoclonal gammopathy without polyneuropathy (MGUS), and healthy controls (HC). We observed an increase in pro-inflammatory cytokines in the CIDP group, whereas interleukin-10 (IL-10) was augmented in the MAGnp patients. These distinctive immune alterations may represent a biological tool in differential diagnosis and future therapeutic approaches.

Myelin protein P0-specific IgM producing monoclonal B cell lines were established from polyneuropathy patients with monoclonal gammopathy of undetermined significance (MGUS)

Monoclonal expansion of B cells and plasma cells, producing antibodies against 'self' molecules, can be found not only in different autoimmune diseases, such as peripheral neuropathy (PN), but also in malignancies, such as Waldenström's macroglobulinaemia and B-type of chronic lymphocytic leukaemia (B-CLL), as well as in precancerous conditions including monoclonal gammopathy of undetermined significance (MGUS). About 50% of patients with PN-MGUS have serum antibodies against peripheral nerve myelin, but the specific role of these antibodies remains uncertain. The aims of the study were to establish, and characterize, myelin-specific B cell clones from peripheral blood of patients with PN-MGUS, by selection of cells bearing specific membrane Ig-receptors for myelin protein P0, using beads coated with P0. P0-coated magnetic beads were used for selection of cells, which subsequently were transformed by Epstein--Barr virus. The specificity of secreted antibodies was tested by ELISA. Two of the clones producing anti-P0 antibodies were selected and expanded. The magnetic selection procedure was repeated and new clones established. The cells were CD5+ positive, although the expression declined in vitro over time. The anti-P0 antibodies were of IgM-lambda type. The antibodies belonged to the VH3 gene family with presence of somatic mutations. The IgM reacted with P0 and myelin-associated glycoprotein (MAG), and showed no evidence for polyreactivity, in contrast to other IgM CD5+ clones included in the study as controls. The expanded clones expressed CD80 and HLA-DR, which is compatible with properties of antigen-presenting cells. The immunomagnetic selection technique was successfully used for isolation of antimyelin protein P0-specific clones. The cell lines may provide useful tools in studies of monoclonal gammopathies, leukaemia, and autoimmune diseases, including aspects of antigen-presentation by these cells followed by T cell activation.

Pathogenesis of Guillain-Barré syndrome

Recent neurophysiological and pathological studies have led to a reclassification of the diseases that underlie Guillain-Barré syndrome (GBS) into acute inflammatory demyelinating polyradiculoneuropathy (AIDP), acute motor and sensory axonal neuropathy (AMSAN) and acute motor axonal neuropathy (AMAN). The Fisher syndrome of ophthalmoplegia, ataxia and areflexia is the most striking of several related conditions. Significant antecedent events include Campylobacter jejuni (4-66%), cytomegalovirus (5-15%), Epstein-Barr virus (2-10%), and Mycoplasma pneumoniae (1-5%) infections. These infections are not uniquely associated with any clinical subtype but severe axonal degeneration is more common following C. jejuni and severe sensory impairment following cytomegalovirus. Strong evidence supports an important role for antibodies to gangliosides in pathogenesis. In particular antibodies to ganglioside GM1 are present in 14-50% of patients with GBS, and are more common in cases with severe axonal degeneration associated with any subtype. Antibodies to ganglioside GQ1b are very closely associated with Fisher syndrome, its formes frustes and related syndromes. Ganglioside-like epitopes exist in the bacterial wall of C. jejuni. Infection by this and other organisms triggers an antibody response in patients with GBS but not in those with uncomplicated enteritis. The development of GBS is likely to be a consequence of special properties of the infecting organism, since some strains such as Penner 0:19 and 0:41 are particularly associated with GBS but not with enteritis. It is also likely to be a consequence of the immunogenetic background of the patient since few patients develop GBS after infection even with one of these strains. Attempts to match the subtypes of GBS to the fine specificity of anti-ganglioside antibodies and to functional effects in experimental models continue but have not yet fully explained the pathogenesis. T cells are also involved in the pathogenesis of most or perhaps all forms of GBS. T cell responses to any of three myelin proteins, P2, PO and PMP22, are sufficient to induce experimental autoimmune neuritis. Activated T cells are present in the circulation in the acute stage, up-regulate matrix metalloproteinases, cross the blood-nerve barrier and encounter their cognate antigens. Identification of the specificity of these T cell responses is still at a preliminary stage. The invasion of intact myelin sheaths by activated macrophages is difficult to explain according to a purely T cell mediated mechanism. The different patterns of GBS are probably due to the diverse interplay between antibodies and T cells of differing specificities.

GM1 ganglioside for acute ischemic stroke. Trial design issues

GM1 ganglioside decreases the severity of ischemic brain lesions in experimental models, although the mechanism is uncertain. In clinical trials involving patients with stroke, efficacy has been reported in some but not in others. However, some of the latter also showed efficacy after analyses not planned before the trial began. Analyses of the trials done to date revealed design differences sufficiently large so as to preclude meta-analysis of the results. Moreover, flaws in these studies may account for some of their failure to demonstrate that GM1 therapy is efficacious in ischemic stroke. Several of these flaws are discussed, including small sample size; attrition of the study cohort; inclusion of stroke severity and type that made demonstrations of a beneficial effect difficult; use of inappropriate clinical and outcome measuring instruments; delay in enrollment; inappropriate statistical analyses; inadequate dose; inappropriate route of administration; a too short duration of treatment. Improvements in these design features in future clinical trials of GM1 may yet demonstrate efficacy of this drug in acute ischemic stroke.

Cytokine production and the pathogenesis of experimental autoimmune neuritis and Guillain-Barré syndrome

Acute inflammatory demyelinating polyradiculoneuropathy (Guillain-Barré syndrome, GBS) and its animal model experimental autoimmune neuritis (EAN) are prototypes of T cell-mediated autoimmune diseases affecting the peripheral nervous system (PNS). Perivascular accumulation of macrophages and T lymphocytes in the PNS, and high levels systemically of PNS myelin antigen-reactive T cells are characteristic features of both diseases, thereby suggesting a pathogenic role for immunoregulatory cytokines. Here we summarise recent studies that have clearly documented that Th1/Th2/Th3 cytokines are differently upregulated during various clinical phases of EAN and GBS. The observations indicate that the role of cytokines in immune regulation and autoimmune disease is more complex than a simple Th1-Th2 dichotomy would suggest. New treatments may be searched for that counteract this complex cytokine imbalance. Treatments with antibodies that selectively target certain pro-inflammatory cytokines, as well as with immunomodulatory preparations that promote cytokines that beneficially influence the disease course should be in focus of future therapeutic trials.

Vascular permeability in the peripheral autonomic and somatic nervous systems: controversial aspects and comparisons with the blood-brain barrier

Endothelium, choroidal epithelium, and arachnoid exclude plasma proteins from most parts of the mammalian central nervous system (CNS). Nerve roots, in contrast, have permeable capillaries and permeable pia-arachnoid sheaths. Diffusion of plasma proteins into the cerebrospinal fluid is probably prevented by slow bulk flow along a pressure gradient from the subarachnoid space into the veins of the roots. In nerves, the perineurium prevents diffusion of proteins from the epineurium into the endoneurium. Capillaries within fascicles are permeable to macromolecules, though less so than the microvessels of roots and ganglia. Endoneurial vascular permeability is lowest in rats and mice, but even in these species albumin is normally present in the extracellular spaces around the nerve fibers. The so-called blood-nerve barrier is not equivalent to the blood-brain barrier. Capillaries in sensory and sympathetic ganglia are fully permeable to macromolecules, and extravasated protein is in contact with neuronal cell bodies and neurites. An impenetrable perineurium surrounds each ganglion, but serves no obvious purpose when the vessels inside are as permeable as those outside. The enteric nervous system lacks a perineurium, and the neurons in its avascular ganglia and tracts are exposed to extracellular fluid formed by permeable vessels in adjacent tissues of the gut. The reasons for excluding macromolecules from some parts of the nervous system are obscure. Carrier-mediated transport, which maintains a constant supply of ions, glucose, and other metabolites to cells in the CNS, would be impossible if larger molecules could diffuse freely. Presumably the metabolic needs of ganglia are adequately met by exchange vessels similar to those of nonnervous tissues. Most of the CNS is protected from exogenous toxic substances that bind to plasma proteins. Peripheral neurons and glial cells are damaged by some such substances because of the lack of blood-tissue barriers.

CD5 expression on B cells may be an activation marker for secretion of anti-myelin antibodies in patients with polyneuropathy associated with monoclonal gammopathy

B cells expressing the CD5 marker belong to a subpopulation with potential autoreactive properties. Increased proportions of CD5+ B cells have been reported in autoimmune diseases. In patients with monoclonal gammopathy and demyelinating polyneuropathy, the M-component often consists of autoantibodies reacting with myelin components. We therefore investigated if CD5+ B cells were involved in the production of anti-myelin antibodies. There was no difference of mean value of CD5+ B cells between patients and controls. However, the proportion of CD5+ B cells was significantly correlated with the amount of anti-myelin antibodies. In seven patients, CD5+ B cells were enriched using an immunomagnetic technique. The number of CD5+ and CD5- B cells secreting anti-myelin antibodies was determined by ELISPOT. In two patients with high levels of antibodies, antibody-secreting cells were mainly, but not exclusively, CD5+ B cells. In five patients with low levels of antibodies, most cells secreting anti-myelin antibodies were CD5-. We conclude that CD5 expressed on B cells may be an activation marker, reflecting B cells producing high amounts of anti-myelin antibodies in patients with polyneuropathy associated with monoclonal gammopathy.

Avidity distribution of antibodies against peripheral nerve myelin in patients with polyneuropathy associated with IgM monoclonal gammopathy and in healthy controls

To elucidate the role and nature of antibodies against peripheral nerve myelin (PNM) we studied their avidity distribution. Twelve patients with demyelinating polyneuropathy associated with IgM monoclonal gammopathy were compared with 12 healthy blood donors previously found to have anti-PNM antibodies of IgM isotype. For comparison, the avidity distribution of IgM antibodies against the varicella zoster antigen in 10 patients with herpes zoster infection was also studied. Microtitre plates containing antibody bound to antigen were exposed to increasing concentrations of sodium thiocyanate (NaSCN) followed by an ELISA assay. NaSCN changes the ion strength and the pH, and thereby the critical conditions for antibody-antigen binding. Resistance to NaSCN was used as a measure of antibody avidity. Anti-PNM antibodies from patients with monoclonal gammopathy were of predominantly low avidity whereas antibodies from blood donors were of predominantly high avidity. Avidity index, representing the molar concentration of NaSCN required to reduce the initial absorbance values by 50%, was on average 11.7 times higher in blood donors (range 0.24-2.65, mean = 0.82) than in patients with monoclonal gammopathy (range 0.04-0.10, mean = 0.07) (p = 0.002). On the other hand, patients with monoclonal gammopathy had on average a 100-fold higher relative concentration of antibodies against PNM compared to blood donors (range 4.1-392.6 AU, mean 85.0 AU, and range 0.2-1.7 AU, mean 0.85 AU, respectively) (p = 0.002). Antibodies against the varicella zoster antigen from patients with herpes zoster showed a high avidity index (range 0.25-2.6, mean = 1.24). Using Western blot, several 14-30 kDa proteins in PNM were found to be the target antigen for IgM anti-PNM antibodies in both patients with monoclonal gammopathy and polyneuropathy, and in blood donors.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification and characterization of natural antibodies that recognize a human brain lectin

We have recently identified oligoclonal IgG antibodies that are related to a human brain lectin (HBL14) from serum and cerebrospinal fluid of patients with neurological disorders. They were termed lectin-like IgG (L-IgG) (Joubert-Caron et al., 1994a,b). In this paper, the occurrence of antibodies reactive both towards HBL14 and L-IgG was investigated. Binding of antibodies to HBL14 was demonstrated by solid-phase ELISA and chromatography on immobilized HBL14. Fab fragments of these antibodies were also shown to bind to HBL14. The specificity of the antibodies towards HBL14 was studied using a panel of different antigens. Our data show that individual sera from healthy people as well as a pool of immunoglobulins from 80 blood donors contain an IgG autoreactivity to HBL14, while no IgM autoreactivity was detected. Anti-HBL14 antibodies from sera were purified using affinity chromatography on immobilized HBL14. Affinity chromatography further allowed us to demonstrate that the binding of anti-HB14 antibodies was mediated through their Fab fragments. A higher amount of anti-HBL14 antibodies was purified using a L-IgG-depleted fraction of sera. The binding of anti-HBL14 antibodies to L-IgG was confirmed by ELISA. Finally, anti-HBL14 antibodies were found to be polyreactive. These results indicate the occurrence of a novel class of natural antibodies reactive towards a human brain lectin and suggest that these antibodies may participate in immunoregulatory mechanisms probably though idiotypic/anti-idiotypic interaction.

Immunopathogenesis and treatment of the Guillain-Barré syndrome--Part I

The etiology of the Guillain-Barré syndrome (GBS) still remains elusive. Recent years have witnessed important advances in the delineation of the mechanisms that may operate to produce nerve damage. Evidence gathered from cell biology, immunology, and immunopathology studies in patients with GBS and animals with experimental autoimmune neuritis (EAN) indicate that GBS results from aberrant immune responses against components of peripheral nerve. Autoreactive T lymphocytes specific for the myelin antigens P0 and P2 and circulating antibodies to these antigens and various glycoproteins and glycolipids have been identified but their pathogenic role remains unclear. The multiplicity of these factors and the involvement of several antigen nonspecific proinflammatory mechanisms suggest that a complex interaction of immune pathways results in nerve damage. Data on disturbed humoral immunity with particular emphasis on glycolipid antibodies and on activation of autoreactive T lymphocytes and macrophages will be reviewed. Possible mechanisms underlying initiation of peripheral nerve-directed immune responses will be discussed with particular emphasis on the recently highlighted association with Campylobacter jejuni infection.

Abnormalities in T-lymphocyte populations in blood from patients with demyelinating polyneuropathy associated with monoclonal gammopathy

Patients with monoclonal gammopathy secrete monoclonal antibodies (M-component), that in some patients are associated with polyneuropathy. The M-component has been shown to react with peripheral nerve myelin in some of these patients. However, it is not known whether the M-component secreting B-cells are autonomous or subject to regulation by T-cells or if other cellular abnormalities may occur. In order to define circulating lymphocyte subpopulations, flow cytometry was done on blood samples from patients with monoclonal gammopathy and demyelinating polyneuropathy (n = 13) and patients with monoclonal gammopathy without polyneuropathy (n = 11), and were compared to healthy controls. Significantly increased proportions of primed T-helper (CD4+) cells, i.e. those expressing helper/inducer function (CD29+ CD4+), providing help for antibody secretion, as well as decreased proportions of naive, unprimed suppressor/inducer (CD45RA+ CD4+) T-helper cells were found in patients with M-component associated polyneuropathy. Within the T-cytotoxic/suppressor population (CD8+) we found an increased proportion of killer/effector (S6F1+ CD8+) cells and a decreased proportion of suppressor/effector (S6F1- CD8+) cells in patients with monoclonal gammopathy and polyneuropathy. Similar findings were found in monoclonal gammopathy patients without polyneuropathy, although the deviations in general were less pronounced and did not reach statistical significance compared to the controls. The proportion of natural killer (NK) cells (CD56+) was markedly decreased in all patients with monoclonal gammopathy. In the whole group of patients with monoclonal gammopathy, we found clear proportions of interleukin-2 receptor (CD25+) expressing lymphocytes, indicating the presence of activated T-cells. No clear correlation between abberations in T-cell subtypes and clinical severity of the demyelinating polyneuropathy or titres of anti-PNM antibodies was found.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunofixation superior to plasma agarose electrophoresis in detecting small M-components in patients with polyneuropathy

Monoclonal immunoglobulins (M-components) in blood are found in some patients with polyneuropathy and are thought to be of pathogenetic importance, especially if the M-component is of IgM isotype. As the finding of an M-component may indicate a treatable polyneuropathy, the potential of the method to uncover an M-component is of importance. Cellulose acetate or agarose electrophoresis used in routine practice may miss small M-components covered by other proteins. We therefore applied the uncovering and specific method of immunofixation in comparison with agarose electrophoresis on patients investigated for polyneuropathy. Of 83 consecutive patients, 5 had M-components. Two of these 5 patients, one with an axonal polyneuropathy and the other with a lower motor neuron syndrome, had extra bands on agarose electrophoresis, verified as IgG M-components by immunofixation. In the 3 additional patients an M-component was uncovered only by immunofixation, not seen in the agarose electrophoresis of plasma; 2 of them were of IgM isotype and one was of IgG isotype. These 3 patients were diagnosed as having a demyelinating (i.e., possibly immune-mediated) polyneuropathy by means of neurophysiology and in one by means of nerve biopsy. A 6th patient had 2 small bands in the gamma region on the agarose electrophoresis, verified as oligoclonal bands of IgG isotype by immunofixation but was not judged as an M-component. Three out of the 83 patients, were judged as having motor neuron diseases. All remaining 80 were found to have polyneuropathy.(ABSTRACT TRUNCATED AT 250 WORDS)

Interleukin-6 levels in the cerebrospinal fluid and serum of patients with Guillain-Barré syndrome and chronic inflammatory demyelinating polyradiculoneuropathy

Clinical and experimental findings suggest that humoral factors, such as anti-peripheral nerve antibodies and cytokines, may be implicated in the immunopathogenesis of Guillain-Barré syndrome (GBS) and chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). Interleukin-6 (IL-6) is a multifunctional cytokine that promotes immunoglobulin synthesis by B lymphocytes. Increased IL-6 release is associated with autoantibody production in a number of immune-mediated and neoplastic disorders. To investigate the possible involvement of abnormal IL-6 release in inflammatory polyneuropathies, we assayed IL-6 levels in the cerebrospinal fluid (CSF) and serum of 23 patients with acute GBS and seven with CIDP. We also studied 69 patients with other non-inflammatory neurological diseases (NIND), 25 with other inflammatory neurological diseases (IND), four with brain tumors (BT), and 15 normal donors (serum alone) as controls. We found detectable levels of IL-6 in the CSF of 57% of GBS, 43% of CIDP, 60% of IND, 75% of BT, and 4% of NIND. In GBS patients, no correlation was found between CSF IL-6 values and other laboratory or clinical parameters, such as CSF total protein, CSF albumin, CSF IgG, CSF/serum albumin ratio, functional disability score, and time elapsed from disease onset. Serum IL-6 levels were increased in six of 23 (26%) GBS, in one of 39 (3%) NIND, and in one of seven (14%) IND, but in none of the CIDP or BT patients. There was no correlation between serum and CSF IL-6 values, but cytokine levels in GBS sera correlated with time elapsed from clinical onset.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Immunochemical and clinical effects of immunosuppressive treatment in monoclonal IgM neuropathy

A pathogenic role of the M protein in monoclonal IgM neuropathy has been suggested. This is based among other things on a close relation between immunosuppressive treatment, lowered concentration of M protein, and clinical effect. We studied five patients with monoclonal IgM and antibodies to peripheral nerve myelin. The immunosuppressive treatment was beneficial in three of the patients. In three patients there was a relationship between antibody concentration and clinical effect (in one there was no change in antibody concentrations and correspondingly no change in clinical status, and in two patients clinical improvement corresponded to decreased antibody concentrations). In two patients, however, there was no clear correlation, since one patient improved despite increasing antibody concentrations and one patient did not improve despite a lowered antibody concentration. It is therefore possible that other mechanisms may contribute to the effect of treatment.