Human autoimmune neuropathies

The effect of myelinating Schwann cells on axons

Myelinating Schwann cells control the number of neurofilaments and elevate the phosphorylation state of neurofilaments in the axon, eventually leading to the typical large axon caliber. Conversely, absence of myelin leads to lower amounts of neurofilaments, reduced phosphorylation levels, and smaller axon diameters. In addition, myelinating Schwann cells mediate the spacing of Na(+) channel clusters during development of the node of Ranvier. When axons are associated with mutant Schwann cells in inherited neuropathies, their calibers are reduced and their neurofilaments are less phosphorylated and more closely spaced. Also, axonal transport is reduced and axons degenerate at the distal ends of long nerves. Myelin-associated glycoprotein may mediate some aspects of Schwann cell-axon communication, but much remains to be learned about the molecular bases of Schwann cell-axon communication.

Campylobacter Enteritis and the Guillain-Barré Syndrome

Campylobacter jejuni is one of the most common causes of bacterial gastroenteritis in the United States and worldwide with approximately 2.4 million infections per year in the United States. A now clearly recognized sequelae following Campylobacter infection is the Guillain-Barré syndrome, an acute immune-mediated attack on the peripheral nervous system. How Campylobacter induces Guillain-Barré syndrome is the subject of intense investigation, and this article discusses some of the recent advances in our understanding of the clinical, epidemiologic, and pathogenic features of the disease.

The role of macrophages in demyelinating peripheral nervous system of mice heterozygously deficient in p0

Mice heterozygously deficient in the p0 gene (P0(+/-)) are animal models for some forms of inherited neuropathies. They display a progressive demyelinating phenotype in motor nerves, accompanied by mild infiltration of lymphocytes and increase in macrophages. We have shown previously that the T lymphocytes are instrumental in the demyelination process. This study addresses the functional role of the macrophage in this monogenic myelin disorder. In motor nerves of P0(+/)- mice, the number of macrophages in demyelinated peripheral nerves was increased by a factor of five when compared with motor nerves of wild-type mice. Immunoelectron microscopy, using a specific marker for mouse macrophages, displayed macrophages not only in the endoneurium of the myelin mutants, but also within endoneurial tubes, suggesting an active role in demyelination. To elucidate the roles of the macrophages, we crossbred the myelin mutants with a spontaneous mouse mutant deficient in macrophage colony-stimulating factor (M-CSF), hence displaying impaired macrophage activation. In the P0-deficient double mutants also deficient in M-CSF, the numbers of macrophages were not elevated in the demyelinating motor nerves and demyelination was less severe. These findings demonstrate an active role of macrophages during pathogenesis of inherited demyelination with putative impact on future treatment strategies.

Intravenous immunoglobulin treatment in peripheral nerve disorders--indications, mechanisms of action and side-effects

This review summarizes observations of clinical use of high dose intravenous immunoglobulin G (IVIg) in regards to administration, kinetics, known or postulated mechanisms of action, and adverse reactions. Indications and value of IVIg for the treatment of various neuropathies with presumed autoimmune aetiology are examined. New knowledge that advances the understanding of the pathogenesis of the neuropathies and of the mechanisms of action of IVIg is discussed.

Paraneoplastic syndromes: an unsolved murder

With neuroimmunology playing an ever greater role in child neurology, paraneoplastic syndromes--uncommon but often devastating complications of cancer--are in the forefront. Abnormalities of both humoral and cellular immunity support the immunological theory of causation. Through co-complicity of host and tumor factors, targets of immunologically mediated injury remote from the tumor may be damaged or destroyed, giving rise to discrete neurological deficits. In the nervous system, the main targets are neuronal nuclei or cell bodies, structural constituents, surface receptors, synapses, and ion channels. The clinical syndromes and response to treatment differ substantially between children and adults. Current pharmacological and biological therapies, which are nonselective, include noncytotoxic and cytotoxic drugs, intravenous immunoglobulins, plasma exchange, and immunoadsorption, some chosen for induction and others for maintenance. Tumor resection and thymectomy are surgical treatments. Combination immunotherapies allow steroid sparing, targeting of more than one immunologic effector pathway, and deploy an advantageous mixture of early- and late-acting drugs. More selective and efficacious immunotherapies are needed.

New concepts of Guillain-Barré syndrome

Guillain-Barré syndrome is an acute autoimmune polyradiculoneuropathy with a clinical presentation of flaccid paralysis with areflexia, variable sensory disturbance, and elevated cerebrospinal fluid protein without pleocytosis. Although Guillain-Barré syndrome previously had been viewed as a unitary disorder with variations, it currently is viewed as a group of syndromes with several distinctive subtypes. These include the principal subtype prevalent in the Western world (acute inflammatory demyelinating polyradiculoneuropathy, and others, each with distinctive electrodiagnostic and pathologic features, including acute motor axonal neuropathy), acute motor-sensory axonal neuropathy, Miller Fisher syndrome, and perhaps others. The clinical and pathologic features of these Guillain-Barré syndrome subtypes are reviewed, and the role of antecedent infections, particularly Campylobacter jejuni gastroenteritis, and the role of antiganglioside antibody responses are reviewed with respect to pathogenesis. Treatment of Guillain-Barré syndrome includes both important supportive measures and immunotherapies, specifically high-dose intravenous immunoglobulin and plasma exchange.

Neuromuscular disorders of childhood

Neuromuscular disorders are common causes of weakness and hypotonia in the infantile period and in childhood. Accurate diagnosis of specific neuromuscular disorders depends first on identification of which aspect of the peripheral neuromuscular system is affected--the motor neuron in the spinal cord, the nerve root or peripheral nerve, the neuromuscular junction, or the muscle--and then on the determination of the etiology and specific clinical entity. This review provides an overview of the major neuromuscular disorders of childhood with attention to recent advances and emerging areas of research.

Induction of adhesion molecules on human schwann cells by proinflammatory cytokines, an immunofluorescence study

The presence of cytokines in the peripheral nerve was positively correlated to the induction and progression of inflammation during experimental allergic neuritis (EAN) and Guillain Barré syndrome (GBS). We investigated the induction of adhesion molecules such as L-selectin, E-selectin, ICAM-1, VCAM-1 and Mac-1 on Schwann cells by proinflammatory cytokines. Cultured human Schwann cells from normal adult, fetal and diabetic nerves were studied by immunofluorescence at basal condition and after stimulation with cytokines for 6, 24, 48 and 96 h. Incubation of human Schwann cells with TNFalpha, IFNgamma and IL-1beta induces the expression of ICAM-1 starting at 6 h and reaching a peak at 24 h on more than 90% of cells. VCAM-1 expression was induced after 6 h of treatment with TNFalpha and IL-1beta on almost 100% of Schwann cells. Surprisingly, stimulation with TNFalpha, IFNgamma and IL-1beta also induced the expression of L-selectin on fetal and diabetic Schwann cells, but not on normal adult cells. E-selectin, an adhesion molecule classically upregulated during inflammation, as well as Mac-1, a ligand for ICAM-1, were not expressed on human Schwann cells at basal condition or after treatment with cytokines. No ICAM-1, VCAM-1 and L-selectin expression was found on unstimulated Schwann cells. Our results suggest that upregulation of adhesion molecules on Schwann cells may have a role in the pathogenesis of inflammation in the peripheral nerve.

Guillain-Barré syndrome

The concepts of Guillain-Barré syndrome have changed substantially over the last 10 years, and the last 2 years have been no exception. Guillain-Barré syndrome is now recognized as a heterogeneous disorder with many clinical manifestations. Most current investigations are centered on the hypothesis of molecular mimicry. The major challenge now is to identify the precise mechanisms of nerve fiber injury and to determine how to prevent immune injury.

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.

Mechanisms of immune regulation in the peripheral nervous system

The peripheral nervous system (PNS) is a target for heterogenous immune attacks mediated by different components of the systemic immune compartment. T cells, B cells, and macrophages can interact with endogenous, partially immune-competent glial cells and contribute to local inflammation. Cellular and humoral immune functions of Schwann cells have been well characterized in vitro. In addition, the interaction of the humoral and cellular immune system with the cellular and extracellular components in the PNS may determine the extent of tissue inflammation and repair processes such as remyelination and neuronal outgrowth. The animal model experimental autoimmune neuritis (EAN) allows direct monitoring of these immune responses in vivo. In EAN contributions to regulate autoimmunity in the PNS are made by adhesion molecules and by cytokines that orchestrate cellular interactions. The PNS has a significant potential to eliminate T cell inflammation via apoptosis, which is almost lacking in other tissues such as muscle and skin. In vitro experiments suggest different scenarios how specific cellular and humoral elements in the PNS may sensitize autoreactive T cells for apoptosis in vivo. Interestingly several conventional and novel immunotherapeutic approaches like glucocorticosteroids and high-dose antigen therapy induce T cell apoptosis in situ in EAN. A better understanding of immune regulation and its failure in the PNS may help to develop improved, more specific immunotherapies.

The role of integrins in immune-mediated diseases of the nervous system

Immune-mediated diseases of the CNS and PNS, such as multiple sclerosis and Guillain-Barré syndrome, respectively, constitute a major cause of transient and permanent neurological disability in the adult. The aetiology and pathogenesis of these disorders are only partially understood. On a cellular level, focal mononuclear-cell infiltration with demyelination and eventual axonal loss is a crucial pathogenetic event that leads to inflammation and subsequent dysfunction. Here, the evidence that integrins, a family of cell adhesion molecules, expressed on neural and immune cells might play a central role in immune cell recruitment to the CNS and PNS, and probably in tissue repair is reviewed. Distinct integrin expression patterns are observed in multiple sclerosis and Guillain-Barré syndrome. Therapeutic targeting of integrins has been very successful in the corresponding animal models and holds promise as a novel treatment strategy to combat human immune-mediated disorders of the nervous system.

Campylobacter species and Guillain-Barré syndrome

Since the eradication of polio in most parts of the world, Guillain-Barré syndrome (GBS) has become the most common cause of acute flaccid paralysis. GBS is an autoimmune disorder of the peripheral nervous system characterized by weakness, usually symmetrical, evolving over a period of several days or more. Since laboratories began to isolate Campylobacter species from stool specimens some 20 years ago, there have been many reports of GBS following Campylobacter infection. Only during the past few years has strong evidence supporting this association developed. Campylobacter infection is now known as the single most identifiable antecedent infection associated with the development of GBS. Campylobacter is thought to cause this autoimmune disease through a mechanism called molecular mimicry, whereby Campylobacter contains ganglioside-like epitopes in the lipopolysaccharide moiety that elicit autoantibodies reacting with peripheral nerve targets. Campylobacter is associated with several pathologic forms of GBS, including the demyelinating (acute inflammatory demyelinating polyneuropathy) and axonal (acute motor axonal neuropathy) forms. Different strains of Campylobacter as well as host factors likely play an important role in determining who develops GBS as well as the nerve targets for the host immune attack of peripheral nerves. The purpose of this review is to summarize our current knowledge about the clinical, epidemiological, pathogenetic, and laboratory aspects of campylobacter-associated GBS.