Guillain-Barré syndrome serum and anti-Campylobacter antibody do not exacerbate experimental autoimmune neuritis

Novel pathomechanisms in inflammatory neuropathies

Inflammatory neuropathies are rare autoimmune-mediated disorders affecting the peripheral nervous system. Considerable progress has recently been made in understanding pathomechanisms of these disorders which will be essential for developing novel diagnostic and therapeutic strategies in the future. Here, we summarize our current understanding of antigenic targets and the relevance of new immunological concepts for inflammatory neuropathies. In addition, we provide an overview of available animal models of acute and chronic variants and how new diagnostic tools such as magnetic resonance imaging and novel therapeutic candidates will benefit patients with inflammatory neuropathies in the future. This review thus illustrates the gap between pre-clinical and clinical findings and aims to outline future directions of development.

Inflammatory neuropathies: pathology, molecular markers and targets for specific therapeutic intervention

Inflammatory neuropathies encompass groups of heterogeneous disorders characterized by pathogenic immune-mediated hematogenous leukocyte infiltration of peripheral nerves, nerve roots or both, with resultant demyelination or axonal degeneration or both. Inflammatory neuropathies may be divided into three major disease categories: Guillain-Barré syndrome (particularly the acute inflammatory demyelinating polyradiculoneuropathy variant), chronic inflammatory demyelinating polyradiculoneuropathy and nonsystemic vasculitic neuropathy (or peripheral nerve vasculitis). Despite major advances in molecular biology, pathology and genetics, the pathogenesis of these disorders remains elusive. There is insufficient knowledge on the mechanisms of hematogenous leukocyte trafficking into the peripheral nervous system to guide the development of specific molecular therapies for immune-mediated inflammatory neuropathies compared to disorders such as psoriasis, inflammatory bowel disease, rheumatoid arthritis or multiple sclerosis. The recent isolation and characterization of human endoneurial endothelial cells that form the blood-nerve barrier provides an opportunity to elucidate leukocyte-endothelial cell interactions critical to the pathogenesis of inflammatory neuropathies at the interface between the systemic circulation and peripheral nerve endoneurium. This review discusses our current knowledge of the classic pathological features of inflammatory neuropathies, attempts at molecular classification and genetic determinants, the utilization of in vitro and in vivo animal models to determine pathogenic mechanisms at the interface between the systemic circulation and the peripheral nervous system relevant to these disorders and prospects for future potential molecular pathology biomarkers and targets for specific therapeutic intervention.

Cellular targets and mechanistic strategies of remyelination-promoting IgMs as part of the naturally occurring autoantibody repertoire

Immunoglobulins with germline sequences occur in invertebrates and vertebrates and are named naturally occurring autoantibodies (NAbs). NAbs may target foreign antigens, self- or altered self-components and are part of the normal immunoglobulin repertoire. Accumulating evidence indicates that naturally occurring antibodies can act as systemic surveillance molecules, which tag, damaged or stressed cells, invading pathogens and toxic cellular debris for elimination by the immune system. In addition to acting as detecting molecules, certain types of NAbs actively signal in different cell types with a broad range of responses from induction of apoptosis in cancer cells to stimulation of remyelination in glial cells. This review emphasizes functions and characteristics of NAbs with focus on remyelination-promoting mouse and human antibodies. Human remyelination-promoting NAbs are potential therapeutics to combat a wide spectrum of disease processes including demyelinating diseases like multiple sclerosis. We will highlight the identified glycosphingolipid (SL) antigens of polyreactive remyelination-promoting antibodies and their proposed mechanism(s) of action. The nature of the identified antigens suggests a lipid raft-based mechanism for remyelination-promoting antibodies with SLs as most essential raft components. However, accumulating evidence also suggests involvement of other antigens in stimulation of remyelination, which will be discussed in the text.

Lewis rats immunized with GM1 ganglioside do not develop peripheral neuropathy

Elevated levels of anti-GM1 antibodies are associated with motor nerve syndromes. Although there is a lot of circumstantial evidence that anti-GM1 antibodies may be causing the disease, their precise role remains unclear. In order to study the role of anti-GM1 antibodies in the pathogenesis of peripheral neuropathy, eight Lewis rats were injected with GM1 ganglioside mixed with keyhole limpet hemocyanin (KLH) and emulsified with Freund's adjuvant and three rats were immunized with GM1 in liposomes. Although IgM class anti-GM1 antibodies were detected in all animals immunized with GM1, none of the animals exhibited overt signs of neuropathy during 6 months after initial immunization. IgG antibody to GM1 was not produced in any of the animals. There was no pathological evidence of nerve damage. These studies suggest that elevated levels of IgM anti-GM1 antibodies by themselves do not cause nerve damage in rats.

Lipooligosaccharide of Campylobacter jejuni prevents myelin-specific enteral tolerance to autoimmune neuritis—a potential mechanism in Guillain-Barré syndrome?

Campylobacter jejuni-induced enteritis is the most common infection preceding Guillain-Barre syndrome (GBS), an immune-mediated polyradiculoneuritis. The acute autoimmune attack is thought to be based on C. jejuni antigens which may mimick antigens of the peripheral nervous system. Additional pathomechanisms, like disturbance of natural T cell immunoregulation by C. jejuni, have not been evaluated so far. In experimental autoimmune neuritis (EAN), a T lymphocyte-mediated animal model of human GBS, tolerance to myelin-derived autoantigens can be induced by oral feeding of the respective antigen. Here we investigated whether the lipooligosaccharide (LOS) fraction of C. jejuni may directly alter immunologic tolerance through gastrointestinal pathways. While EAN, actively induced by immunization with bovine peripheral nerve myelin could be ameliorated by precedent feeding of myelin, feeding of C. jejuni LOS along with the myelin antigen not only prevented the tolerizing effects of oral myelin but even accelerated the onset of overt EAN and augmented the myelin-specific B cell response. These findings provide evidence that LOS of C. jejuni, as produced in the gut during C. jejuni-induced enteritis, can disturb natural tolerance to definite proteins which may be or may mimic peripheral nerve antigens. In human patients this may be one of the potential mechanisms to explain why C. jejuni enteritis is a common trigger of GBS.

Antiglycolipid antibodies in Guillain-Barré syndrome and related diseases: Review of clinical features and antibody specificities

Guillain-Barré syndrome (GBS) is an acute inflammatory polyradiculoneuropathy that usually develops following a respiratory or intestinal infection. Although the pathogenic mechanisms of GBS have not been fully established, both humoral and cell-mediated immune factors have been shown to contribute to the disease process. Several antiglycosphingolipid (anti-GSL) antibodies have been found in the sera of patients with GBS or related diseases. Measurements of these antibody titers are very important in the diagnosis of GBS and in evaluating the effectiveness of treatments in clinical trials. The most common treatment strategies for these disorders involve plasmapheresis and the use of steroids for reducing anti-GSL antibody titers to ameliorate patients' clinical symptoms. Administration of intravenous immunoglobulin may also be beneficial in the treatment of neuropathies by suppressing the immune-mediated processes that are directed against antigenic targets in myelin and axons. In certain demyelinating neuropathies, the destruction or malfunctioning of the blood-nerve barrier, which results in the leakage of circulating antibodies into the peripheral nerve parenchyma, has been considered to be an initial step in development of the disease process. In addition, anti-GSL antibodies, such as anti-GM1, may cause nerve dysfunction and injury by interfering with the ion channel function at the nodes of Ranvier, where carbohydrate epitopes of glycoconjugates are located. These malfunctions thus contribute to the pathogenic mechanisms of certain demyelinating neuropathies.

An anti-ganglioside antibody-secreting hybridoma induces neuropathy in mice

Immune responses against gangliosides are strongly implicated in the pathogenesis of some variants of Guillain-Barré syndrome (GBS). For example, IgG antibodies against GM1, GD1a, and related gangliosides are frequently present in patients with post-Campylobacter acute motor axonal neuropathy (AMAN) variant of GBS, and immunization of rabbits with GM1 has produced a model of AMAN. However, the role of anti-ganglioside antibodies in GBS continues to be debated because of lack of a passive transfer model. We recently have raised several monoclonal IgG anti-ganglioside antibodies. We passively transfer these antibodies by intraperitoneal hybridoma implantation and by systemic administration of purified anti-ganglioside antibodies in mice. Approximately half the animals implanted with an intraperitoneal clone of anti-ganglioside antibody-secreting hybridoma developed a patchy, predominantly axonal neuropathy affecting a small proportion of nerve fibers. In contrast to hybridoma implantation, passive transfer with systemically administered anti-ganglioside antibodies did not cause nerve fiber degeneration despite high titre circulating antibodies. Blood-nerve barrier studies indicate that animals implanted with hybridoma had leaky blood-nerve barrier compared to mice that received systemically administered anti-ganglioside antibodies. Our findings suggest that in addition to circulating antibodies, factors such as antibody accessibility and nerve fiber resistance to antibody-mediated injury play a role in the development of neuropathy.

Blood ?? T cells,Campylobacter jejuni, and GM1 titers in Guillain-Barr� syndrome

The gammadelta T cells participate in microbial defense, are prevalent in intestinal epithelia, and are activated in autoimmune diseases. We studied whether peripheral blood gammadelta cells and gammadelta subsets are increased in Guillain-Barré syndrome (GBS) and whether elevations are associated with Campylobacter jejuni infection or GM1 elevations. In 20 GBS patients, we performed serial flow cytometry studies of blood gammadelta, Vdelta1, and Vdelta2 cells (+/- CD8+), C jejuni, and ganglioside titers. There was no significant difference in median gammadelta T-cell percentages between GBS patients and controls at onset and at convalescence. However, 5 patients had marked Vdelta1/CD8+ elevations. Elevated Vdelta1 or Vdelta1/CD8+ cells occurred in 3 of 6 patients with C jejuni or GM1 titer elevations. A minority of GBS patients have elevations of Vdelta1/CD8+ cells, possibly associated with elevated C jejuni or GM1 titers. The gammadelta T cells may have a cytotoxic (or suppressor) role in the disease.

Advances in understanding and treatment of immune-mediated disorders of the peripheral nervous system

During recent years, novel insights in basic immunology and advances in biotechnology have contributed to an increased understanding of the pathogenetic mechanisms of immune-mediated disorders of the peripheral nervous system. This increased knowledge has an impact on the management of patients with this class of disorders. Current advances are outlined and their implication for therapeutic approaches addressed. As a prototypic immune-mediated neuropathy, special emphasis is placed on the pathogenesis and treatment of the Guillain-Barré syndrome and its variants. Moreover, neuropathies of the chronic inflammatory demyelinating, multifocal motor, and nonsystemic vasculitic types are discussed. This review summarizes recent progress with currently available therapies and--on the basis of present immunopathogenetic concepts--outlines future treatment strategies.

The relation of clinical symptoms and anti-ganglioside antibodies to MEPPs frequency increase in 8 cases of variant type Guillain-Barré syndrome

Many patients with variant forms of Guillain-Barré syndrome (vGBS) associated with anti-ganglioside antibodies, including Miller Fisher syndrome (MFS), sometimes exhibit miniature endplate potential (MEPP) frequency increases (MFI, described as alpha-latrotoxin-like effects in a previous report) and the factor to produce this effect is present in their sera. MFI-positive sera increase the frequency of MEPPs, then block neuromuscular transmission at the mouse neuromuscular junction. A connection between this effect at the neuromuscular junction and some vGBS symptoms is suspected. We measured MFI directly at several points during the clinical course of 8 vGBS patients who had various symptoms and courses. Six patients had confirmed MFI and this activity decreased with convalescence. In 3 clinically mild cases, we were able to elicit MFI using normal serum to supply complement after exposure to the patient's serum. The anti-GQ1b/GT1a IgG titer, the extent of ophthalmoplegia and the extent of MFI were significantly correlated. They did not correlate with the severity of limb weakness or the occurrence of respiratory failure. These results support the hypothesis that MFI caused by anti-ganglioside antibodies is the pathogenic mechanism responsible for ophthalmoplegia in vGBS; different mechanisms or antibodies may explain limb weakness and respiratory failure. Furthermore, MFI may be an important indicator of how serum injures the nerve terminals. The symptoms of vGBS may result from multiple pathogenic factors.