Animal models of immune-mediated neuropathies

Immune Modifying Effect of Drug Free Biodegradable Nanoparticles on Disease Course of Experimental Autoimmune Neuritis

Guillain-Barre syndrome (GBS) is an autoimmune disease of demyelination and inflammation of peripheral nerves. Current treatments are limited to plasma exchange and intravenous immunoglobulins. Cargo-free nanoparticles (NPs) have been evaluated here for their therapeutic benefit on the disease course of experimental autoimmune neuritis (EAN), mimicking the human GBS. NPs prepared from poly-lactic co-glycolic acid (PLGA) with variable size and surface charge (i.e., 500 nm vs. 130 nm, polyvinyl alcohol (PVA) vs. sodium cholate), were intravenously administered in before- or early-onset treatment schedules in a rat EAN model. NP treatment mitigated distinctly the clinical severity of EAN as compared to the P2-peptide control group (P2) in all treatments and reduced the trafficking of inflammatory monocytes at inflammatory loci and diverted them towards the spleen. Therapeutic treatment with NPs reduced the expression of proinflammatory markers (CD68 (P2: 34.8 ± 6.6 vs. NP: 11.9 ± 2.3), IL-1β (P2: 18.3 ± 0.8 vs. NP: 5.8 ± 2.2), TNF-α (P2: 23.5 ± 3.7 vs. NP: 8.3 ± 1.7) and elevated the expression levels of anti-inflammatory markers CD163 (P2: 19.7 ± 3.0 vs. NP: 41.1 ± 6.5; all for NP-PVA of 130 nm; relative to healthy control). These results highlight the therapeutic potential of such cargo-free NPs in treating EAN, which would be easily translatable into clinical use due to their well-known low-toxicity profile.

Nerve pathology in animal models of neuropathies

To understand the pathology of axonal degeneration and demyelination in peripheral neuropathy, histological investigations in different animal models that mimic some aspects of human peripheral neuropathy are needed. Thus, in the following section of this special issue, the main pathological features of experimental autoimmune neuritis, animal models of chemotherapy-induced peripheral neuropath and of human inherited peripheral neuropathies (IPNs) will be illustrated. When possible, micrographs from animal models and selected human biopsy will be shown side by side.

[Autologous hematopoietic stem cell transplantation for chronic inflammatory demyelinating polyneuropathy]

Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is a dysimmune neuropathy with sensory and/or motor symptoms due to destruction of the myelin sheat secondary to an auto-immune attack. A quarter to a third of patients do not respond to immunomodulatory first line recommended therapies. No second line treatment has shown its effectiveness with a sufficient level of evidence. Autologous hematopoietic stem cell transplantation (AHSCT) is a promising therapy for autoimmune disease, especially for CIDP in recent works. We present in this article an update on the diagnosis of CIDP, its conventional treatments as well as the results of AHSCT in this indication, which was the subject of French recommendations under the aegis of the SFGMTC and neuromuscular disease french faculty (FILNEMUS) as a third line therapy after failure of two first-line and one second-line treatments.

Partial deletion of p75NTR in large-diameter DRG neurons exerts no influence upon the survival of peripheral sensory neurons in vivo

The p75 neurotrophin receptor (p75NTR ) is required for maintaining peripheral sensory neuron survival and function; however, the underlying cellular mechanism remains unclear. The general view is that expression of p75NTR by the neuron itself is required for maintaining sensory neuron survival and myelination in the peripheral nervous system (PNS). Adopting a neuronal-specific conditional knockout strategy, we demonstrate the partial depletion of p75NTR in neurons exerts little influence upon maintaining sensory neuron survival and peripheral nerve myelination in health and after demyelinating neuropathy. Our data show that the density and total number of dorsal root ganglion (DRG) neurons in 2-month-old mice is not affected following the deletion of p75NTR in large-diameter myelinating neurons, as assessed by stereology. Adopting experimental autoimmune neuritis induced in adult male mice, an animal model of demyelinating peripheral neuropathy, we identify that deleting p75NTR in myelinating neurons exerts no influence upon the disease progression, the total number of DRG neurons, and the extent of myelin damage in the sciatic nerve, indicating that the expression of neuronal p75NTR is not essential for maintaining peripheral neuron survival and myelination after a demyelinating insult in vivo. Together, results of this study suggest that the survival and myelination of peripheral sensory neurons is independent of p75NTR expressed by a subtype of neurons in vivo. Thus, our findings provide new insights into the mechanism underpinning p75NTR -mediated neuronal survival in the PNS.

Sulfatides ameliorate experimental autoimmune neuritis by suppressing Th1/Th17 cells

Sulfatides have immunomodulatory functions, and play protective roles in multiple autoimmune diseases. In the present study, we showed that sulfatides ameliorated experimental autoimmune neuritis in Lewis rats induced with bovine peripheral myelin, which was associated with decreased proportions of Th1 and Th17 cells. Furthermore, compared control group, cells from sulfatide-treated rats exhibited lower potential in proliferation and IL-17 secretion in the presence of BPM or ConA in vitro. Moreover, sulfatides also reduced the proportions of NK and NKT cells. In summary, our study indicated that sulfatides might become a new therapeutic agent in Guillain-Barré syndrome in the future.

Immune-mediated neuropathies

Since the discovery of an acute monophasic paralysis, later coined Guillain-Barré syndrome, almost 100 years ago, and the discovery of chronic, steroid-responsive polyneuropathy 50 years ago, the spectrum of immune-mediated polyneuropathies has broadened, with various subtypes continuing to be identified, including chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) and multifocal motor neuropathy (MMN). In general, these disorders are speculated to be caused by autoimmunity to proteins located at the node of Ranvier or components of myelin of peripheral nerves, although disease-associated autoantibodies have not been identified for all disorders. Owing to the numerous subtypes of the immune-mediated neuropathies, making the right diagnosis in daily clinical practice is complicated. Moreover, treating these disorders, particularly their chronic variants, such as CIDP and MMN, poses a challenge. In general, management of these disorders includes immunotherapies, such as corticosteroids, intravenous immunoglobulin or plasma exchange. Improvements in clinical criteria and the emergence of more disease-specific immunotherapies should broaden the therapeutic options for these disabling diseases.

Trapped in the epineurium: early entry into the endoneurium is restricted to neuritogenic T cells in experimental autoimmune neuritis

Background

Autoimmune polyneuropathies are acquired inflammatory disorders of the peripheral nervous system (PNS) characterized by inflammation, demyelination, and axonal degeneration. Although the pathogenesis has not been fully elucidated, T cells recognizing self-antigens are believed to initiate inflammation in a subgroup of patients. However, the route and time of T cell entry into the PNS have not yet been described in detail. In this study, we analyzed both kinetics as well as localization of retrovirally transfected green fluorescent protein (GFP)-expressing neuritogenic T lymphocytes in experimental autoimmune neuritis (EAN).

Methods

T lymphocytes obtained from rats following EAN induction by immunization with peripheral nerve protein peptide P2_55–78 were retrovirally engineered to express GFP. Non-specific T cells were negatively selected by in vitro restimulation, whereas GFP-expressing neuritogenic T cells (reactive to P2_55–78) were adoptively transferred into healthy rats (AT-EAN). Antigen-specific T cell tracking and localization was performed by flow cytometry and immunohistochemistry during the course of disease.

Results

After induction of autoimmune neuritis, P2-reactive T cells were detectable in the liver, spleen, lymph nodes, lung, peripheral blood, and the sciatic nerves with distinct kinetics. A significant number of GFP⁺ T cells appeared early in the lung with a peak at day four. In the peripheral nerves within the first days, GFP-negative T cells rapidly accumulated and exceeded the number of GFP-expressing cells, but did not enter the endoneurium. Very early after adoptive transfer, T cells are found in proximity to peripheral nerves and in the epineurium. However, only GFP-expressing neuritogenic T cells are able to enter the endoneurium from day five after transfer.

Conclusions

Our findings suggest that neuritogenic T cells invade the PNS early in the course of disease. However, neuritogenic T cells cross the blood-nerve barrier with a certain delay without preference to dorsal roots. Further understanding of the pathophysiological role of autoagressive T cells may help to improve therapeutic strategies in immune-mediated neuropathies.

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.

A Brain-Derived Neurotrophic Factor-Based p75NTR Peptide Mimetic Ameliorates Experimental Autoimmune Neuritis Induced Axonal Pathology and Demyelination

Axonal damage and demyelination are major determinants of disability in patients with peripheral demyelinating neuropathies. The neurotrophin family of growth factors are essential for the normal development and myelination of the peripheral nervous system (PNS), and as such are potential therapeutic candidates for ameliorating axonal and myelin damage. In particular, BDNF promotes peripheral nerve myelination via p75 neurotrophin receptor (p75NTR) receptors. Here, we investigated the therapeutic efficacy of a small structural mimetic of the region of BDNF that binds to p75NTR (cyclo-dPAKKR) in experimental autoimmune neuritis (EAN), an established animal model of peripheral demyelinating neuropathy. Examination of rodents induced with EAN revealed that p75NTR is abundantly expressed in affected peripheral nerves. We found that systemic administration of cyclo-dPAKKR ameliorates EAN disease severity and accelerates recovery. Animals treated with cyclo-dPAKKR displayed significantly better motor performance compared to control animals. Histological assessment revealed that cyclo-dPAKKR administration limits the extent of inflammatory demyelination and axonal damage, and protects against the disruption of nodal architecture in affected peripheral nerves. In contrast, a structural control peptide of cyclo-dPAKKR exerted no influence. Moreover, all the beneficial effects of cyclo-dPAKKR in EAN are abrogated in p75NTR heterozygous mice, strongly suggesting a p75NTR-dependent effect. Taken together, our data demonstrate that cyclo-dPAKKR ameliorates functional and pathological defects of EAN in a p75NTR-dependant manner, suggesting that p75NTR is a therapeutic target to consider for future treatment of peripheral demyelinating diseases and targeting of p75NTR is a strategy worthy of further investigation.

Characterization of a new rat model for chronic inflammatory demyelinating polyneuropathies

Our objective was to develop a chronic model of EAN which could be used as a tool to test treatment strategies for CIDP. Lewis rats injected with S-palmitoylated P0(180-199) peptide developed a chronic, sometimes relapsing-remitting type of disease. Our model fulfills electrophysiological criteria of demyelination with axonal degeneration, confirmed by immunohistopathology. The late phase of the chronic disease was characterized by accumulation of IL-17(+) cells and macrophages in sciatic nerves and by high serum IL-17 levels. In conclusion, we have developed a reliable and reproducible animal model resembling CIDP that can now be used for translational drug studies.

FoxP3+ regulatory T cells determine disease severity in rodent models of inflammatory neuropathies

Inflammatory neuropathies represent disabling human autoimmune disorders with considerable disease variability. Animal models provide insights into defined aspects of their disease pathogenesis. Forkhead box P3 (FoxP3)+ regulatory T lymphocytes (Treg) are anti-inflammatory cells that maintain immune tolerance and counteract tissue damage in a variety of immune-mediated disorders. Dysfunction or a reduced frequency of Tregs have been associated with different human autoimmune disorders. We here analyzed the functional relevance of Tregs in determining disease manifestation and severity in murine models of autoimmune neuropathies. We took advantage of the DEREG mouse system allowing depletion of Treg with high specificity as well as anti-CD25 directed antibodies to deplete Tregs in mice in actively induced experimental autoimmune neuritis (EAN). Furthermore antibody-depletion was performed in an adoptive transfer model of chronic neuritis. Early Treg depletion increased clinical EAN severity both in active and adoptive transfer chronic neuritis. This was accompanied by increased proliferation of myelin specific T cells and histological signs of peripheral nerve inflammation. Late stage Treg depletion after initial disease manifestation however did not exacerbate inflammatory neuropathy symptoms further. We conclude that Tregs determine disease severity in experimental autoimmune neuropathies during the initial priming phase, but have no major disease modifying function after disease manifestation. Potential future therapeutic approaches targeting Tregs should thus be performed early in inflammatory neuropathies.

Laquinimod exerts strong clinical and immunomodulatory effects in Lewis rat experimental autoimmune neuritis

Laquinimod is an immunomodulatory drug with neuroprotective potential. We used the animal model of experimental autoimmune neuritis (EAN) in the Lewis rat to study the effects of laquinimod treatment. After immunization with the neuritogenic peptide aa 53-78 of P2 myelin protein, preventive therapy with 12.5mg/kg laquinimod once daily inhibited neuritis in clinical and electrophysiological terms. Histology corroborated a lower degree of inflammatory lesions and demyelination in the sciatic nerve. The proportion of FoxP3-positive regulatory T cells in the peripheral lymph nodes of treated rats remained unchanged. We conclude that laquinimod may represent a therapeutic option in human autoimmune neuropathies.

A new animal model of spontaneous autoimmune peripheral polyneuropathy: implications for Guillain-Barré syndrome

BACKGROUND

Spontaneous autoimmune peripheral neuropathy including Guillain-Barré Syndrome (GBS) represents as one of the serious emergencies in neurology. Although pathological changes have been well documented, molecular and cellular mechanisms of GBS are still under-explored, partially due to short of appropriate animal models. The field lacks of spontaneous and translatable models for mechanistic investigations. As GBS is preceded often by viral or bacterial infection, a condition can enhance co-stimulatory activity; we sought to investigate the critical role of T cell co-stimulation in this autoimmune disease.

RESULTS

Our previous study reported that transgene-derived constitutive expression of co-stimulator B7.2 on antigen presenting cells of the nervous tissues drove spontaneous neurological disorders. Depletion of CD4+ T cells in L31 mice accelerated the onset and increased the prevalence of the disease. In the current study, we further demonstrated that L31/CD4-/- mice exhibited both motor and sensory deficits, including weakness and paresis of limbs, numbness to mechanical stimuli and hypersensitivity to thermal stimulation. Pathological changes were characterized by massive infiltration of macrophages and CD8+ T cells, demyelination and axonal damage in peripheral nerves, while changes in spinal cords could be secondary to the PNS damage. In symptomatic L31/CD4-/- mice, the disruption of the blood neural barriers was observed mainly in peripheral nerves. Interestingly, the infiltration of immune cells was initiated in pre-symptomatic L31/CD4-/- mice, prior to the disease onset, in the DRG and spinal roots where the blood nerve barrier is virtually absent.

CONCLUSIONS

L31/CD4-/- mice mimic most parts of clinical and pathological signatures of GBS in human; thus providing an unconventional opportunity to experimentally explore the critical events that lead to spontaneous, autoimmune demyelinating disease of the peripheral nervous system.

Immune mechanisms in spontaneously occurring CIDP in NOD mice

Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is an autoimmune disease affecting the peripheral nervous system (PNS) and is thought to involve both cellular and humoral immunity. Although its etiology remains to be fully elucidated, the use of animal models has provided some important information regarding its pathogenetic mechanisms. The development of a spontaneous autoimmune polyneuropathy (SAP) in B7-2 knockout non-obese diabetic (NOD) mice underscores the importance of co-stimulatory pathways such as B7-1/B7-2:CD28/CTLA-4 molecules in inflammatory neuropathies. These co-stimulatory molecules regulate the balance between pathogenic and regulatory T cells (Tregs). In SAP, pathogenic T cells are directed against myelin protein zero (P0), the most prominent PNS myelin protein that is a member of immunoglobulin gene superfamily.

Quinpramine ameliorates rat experimental autoimmune neuritis and redistributes MHC class II molecules

Activation of inflammatory cells is central to the pathogenesis of autoimmune demyelinating diseases of the peripheral nervous system. The novel chimeric compound quinpramine—generated from imipramine and quinacrine—redistributes cholesterol rich membrane domains to intracellular compartments. We studied the immunological and clinical effects of quinpramine in myelin homogenate induced Lewis rat experimental autoimmune neuritis (EAN), a model system for acute human inflammatory neuropathies, such as the Guillain-Barré syndrome. EAN animals develop paresis of all limbs due to autoimmune inflammation of peripheral nerves. Quinpramine treatment ameliorated clinical disease severity of EAN and infiltration of macrophages into peripheral nerves. It reduced expression of MHC class II molecules on antigen presenting cells and antigen specific T cell proliferation both in vitro and in vivo. Quinpramine exerted its anti-proliferatory effect on antigen presenting cells, but not on responder T cells. Our data suggest that quinpramine represents a candidate pharmaceutical for inflammatory neuropathies.

Autoimmune diseases of the peripheral nervous system

Autoimmune-mediated diseases targeting the peripheral nerve represent a group of disorders often associated with high clinical disability. At present, therapeutic options are limited. The application of innovative and cutting-edge technologies to the study of immune-mediated disorders of the peripheral nervous system (PNS) have generated a better understanding of underlying principles of the organization of the immune network present in the peripheral nerve and its dialogue with the systemic immune system. These insights may foster the development of specific and highly effective therapies for autoimmune diseases of the peripheral nerve. Of great interest in this context is the application of monoclonal antibodies, such as rituximab or alemtuzumab, which in small observational studies provided promising clinical results. But also other immunomodulatory or immunosuppressive drugs used in other indications currently find their way to PNS autoimmunity. Clearly, prospective controlled clinical trials are warranted before making firm conclusions on the feasibility of these innovative therapeutic approaches for treating immune-mediated disease of the peripheral nerve.

Immunodominant T cell determinants of aquaporin-4, the autoantigen associated with neuromyelitis optica

Autoantibodies that target the water channel aquaporin-4 (AQP4) in neuromyelitis optica (NMO) are IgG1, a T cell-dependent Ig subclass. However, a role for AQP4-specific T cells in this CNS inflammatory disease is not known. To evaluate their potential role in CNS autoimmunity, we have identified and characterized T cells that respond to AQP4 in C57BL/6 and SJL/J mice, two strains that are commonly studied in models of CNS inflammatory diseases. Mice were immunized with either overlapping peptides or intact hAQP4 protein encompassing the entire 323 amino acid sequence. T cell determinants identified from examination of the AQP4 peptide (p) library were located within AQP4 p21-40, p91-110, p101-120, p166-180, p231-250 and p261-280 in C57BL/6 mice, and within p11-30, p21-40, p101-120, p126-140 and p261-280 in SJL/J mice. AQP4-specific T cells were CD4⁺ and MHC II-restricted. In recall responses to immunization with intact AQP4, T cells responded primarily to p21-40, indicating this region contains the immunodominant T cell epitope(s) for both strains. AQP4 p21-40-primed T cells secreted both IFN-γ and IL-17. The core immunodominant AQP4 21-40 T cell determinant was mapped to residues 24-35 in C57BL/6 mice and 23-35 in SJL/J mice. Our identification of the AQP4 T cell determinants and characterization of its immunodominant determinant should permit investigators to evaluate the role of AQP4-specific T cells in vivo and to develop AQP4-targeted murine NMO models.

Circulating subsets and CD4(+)CD25(+) regulatory T cell function in chronic inflammatory demyelinating polyradiculoneuropathy

Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is an inflammatory disease of the peripheral nervous system that is probably autoimmune in origin. Different components of the adaptive and innate immunity may be responsible for the aberrant response towards nerve antigens. To investigate this, we examined lymphocyte subsets and regulatory T cell (Treg) function in the blood of CIDP patients, healthy controls (HC) and subjects with non-immune mediated neuropathies (other neuropathies, ON). We used flow cytometry to determine the frequency of monocytes, B cells, natural killer (NK) and NK-T cells, total and activated CD4(+) and CD8(+) T cells, effector memory and central memory CD4(+) and CD8(+) T cells, and CD4(+)CD25(high)Foxp3(+) Tregs. Treg function was studied after polyclonal stimulation and antigen specific stimulation with myelin protein peptides in CIDP and HC. There was an increased frequency of monocytes (p = 0.02) and decreased frequency of NK cells (p = 0.02) in CIDP compared with HC but not ON. There were no significant differences in other populations. Treg function was impaired in CIDP compared to HC (p = 0.02), whilst T cell proliferation to myelin protein peptides before and after depletion of Tregs was not different between patients and controls. This study shows increased circulating monocytes and reduced NK cells in CIDP. Although Treg frequency was not altered, we confirm that Tregs display a defect of suppressive function. Myelin protein peptides were not the target of the altered peripheral regulation of the immune response. The mechanisms of peripheral immune tolerance in CIDP and their relevance to the pathogenesis deserve further exploration.

Chronic inflammatory demyelinating polyradiculoneuropathy: a role for haematopoietic stem cell transplantation?

Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is a clinical syndrome of a chronic progressive or relapsing and remitting, symmetrical, sensory and motor radiculoneuropathy. The immune reaction in CIDP is characterised by selective inflammation of peripheral nerves and is probably due to the interaction of cellular and humoral responses. Only three treatments for CIDP have demonstrated benefit in randomised studies, corticosteroids, plasma exchange and intravenous immunoglobulin. 25% of patients fail to respond or do not respond adequately to these treatments. Experimental data in animal models have shown that several autoimmune disorders, either congenital or acquired, can be transferred and/or treated by the transplantation of bone marrow stem cells. Haematopoietic stem cell transplantation (HSCT) has been performed with varying success in over 700 patients with autoimmune disorders throughout Europe. The experience in CIDP is very limited. This article will review current understanding of CIDP and experience of the use of HSCT in refractory CIDP.

[The significance of intravenous immunoglobulin in treatment of immune-mediated polyneuropathies]

Long-term treatment of immune-mediated polyneuropathies remains difficult. For acute polyneuritis, or Guillain-Barré syndrome, the established standard therapy utilizes high doses of polyvalent intravenous immunoglobulins (IVIG). A recently published randomized placebo-controlled study of patients with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) showed IVIG to be clinically effective also for this disorder in both short and long term. This survey presents data of this so-called ICE study ("Intravenous immune globulin for the treatment of chronic inflammatory demyelinating polyradiculoneuropathy"). It also discusses the value of IVIG in the treatment of immune-mediated polyneuropathies.

Administration of dehydroepiandrosterone ameliorates experimental autoimmune neuritis in Lewis rats

Dehydroepiandrosterone (DHEA) is an abundant adrenal steroid in serum of humans, and has been reported to have anti-inflammatory, anti-proliferative, and certain immune-regulating properties. Experimental autoimmune neuritis (EAN) is a Th1 cell-mediated animal model of Guillain-Barré syndrome (GBS) in humans. In the present study, DHEA was administered subcutaneously to Lewis rats immunized with bovine peripheral myelin (BPM) in Freund's complete adjuvant. Rats treated with DHEA displayed significant delay in onset, decreased inflammatory cell infiltration in the PNS. Benefit was associated with significant decreases in numbers of IFN-gamma and TNF-alpha expressing cells in the PNS, BPM-stimulated T cell proliferation and IFN-gamma, TNF-alpha-secretion in the spleen cells. Only 2 mg DHEA-treated EAN rats decreased peak clinical score. No significant difference of supernatant IL-10 was found among the treatment and control groups. These results suggest that DHEA can ameliorate the severity of EAN by suppressing the proliferation of autoreactive T cell and expression of pro-inflammatory cytokines.

Intravenous immunoglobulins in the treatment of immune neuropathies

PURPOSE OF REVIEW

The aim of this review is to describe the value of high-dose polyclonal intravenous immunoglobulins as a treatment option in autoimmune disorders affecting the peripheral nervous system.

RECENT FINDINGS

A randomized placebo-controlled trial in patients with chronic inflammatory demyelinating polyradiculoneuropathy revealed short-term and long-term efficacy and safety of intravenous immunoglobulins as a treatment option for the chronically inflamed peripheral nervous system. Case reports suggest that the subcutaneous administration of immunoglobulins may represent a convenient alternative.

SUMMARY

Intravenous immunoglobulin represents an effective and safe treatment option in patients with autoimmune-mediated diseases affecting the peripheral nerves.

The master switch: the role of mast cells in autoimmunity and tolerance

There are many parallels between allergic and autoimmune responses. Both are considered hypersensitivity responses: pathologies that are elicited by an exuberant reaction to antigens that do not pose any inherent danger to the organism. Although mast cells have long been recognized as central players in allergy, only recently has their role in autoimmunity become apparent. Because of the commonalities of these responses, much of what we have learned about the underlying mast cell-dependent mechanisms of inflammatory damage in allergy and asthma can be used to understand autoimmunity. Here we review mast cell biology in the context of autoimmune disease. We discuss the huge diversity in mast cell responses that can exert either proinflammatory or antiinflammatory activity. We also consider the myriad factors that cause one response to predominate over another in a particular immune setting.

The immunocompetence of Schwann cells

Schwann cells are the myelinating glial cells of the peripheral nervous system that support and ensheath axons with myelin to enable rapid saltatory signal propagation in the axon. Immunocompetence, however, has only recently been recognized as an important feature of Schwann cells. An autoimmune response against components of the peripheral nervous system triggers disabling inflammatory neuropathies in patients and corresponding animal models. The immune system participates in nerve damage and disease manifestation even in non-inflammatory hereditary neuropathies. A growing body of evidence suggests that Schwann cells may modulate local immune responses by recognizing and presenting antigens and may also influence and terminate nerve inflammation by secreting cytokines. This review summarizes current knowledge on the interaction of Schwann cells with the immune system, which is involved in diseases of the peripheral nervous system.

Expression of RhoA by inflammatory macrophages and T cells in rat experimental autoimmune neuritis

RhoA is one of the best-studied members of Rho GTPases. Experimental autoimmune neuritis (EAN), which is characterized by infiltration of T cells and macrophages into the peripheral nervous system, is an autoantigen-specific T-cell-mediated animal model of human Guillain-Barré Syndrome. In this study, RhoA expression has been investigated in the dorsal/ventral roots of EAN rats by immunohistochemistry. A significant accumulation of RhoA+ cells was observed on Day 12, with a maximum around Day 15, correlating to the clinical severity of EAN. In dorsal/ventral roots of EAN, RhoA+ cells were seen in perivascular areas but also in the parenchyma. Furthermore, double-labelling experiments showed that the major cellular sources of RhoA were reactive macrophages and T cells. In conclusion, this is the first demonstration of the presence of RhoA in the dorsal/ventral roots of EAN. The time courses and cellular sources of RhoA together with the functions of RhoA indicate that RhoA may function to facilitate macrophage and T-cell infiltration in EAN and therefore could be a potential therapeutic target.

Effective treatment of experimental autoimmune neuritis with human immunoglobulin

High-dose intravenous immunoglobulin (IVIg) is an effective treatment for inflammatory demyelinating neuropathies, although the mechanism(s) of action remain incompletely understood. Experimental autoimmune neuritis (EAN) is an animal model of inflammatory demyelinating neuropathies; however, there have been conflicting reports regarding the efficacy of human IVIg in EAN. To obtain a model suitable for the study of the mechanism(s) of action of IVIg in Guillain-Barré syndrome, we investigated the effect of IVIg in EAN in the rat using clinical, electrophysiological and morphological measures. Human IVIg administered at the onset of signs of disease proved effective in preventing further progression of disease and shortening disease duration. This effectiveness was associated with significant differences in electrophysiological parameters including less prolongation of somatosensory evoked potential (S wave) latencies, better maintained S wave amplitudes, less reduction of distal motor nerve conduction velocity, and better maintained amplitudes of compound muscle action potentials of the dorsal foot muscles after stimulation at ankle and hip. Moreover, treatment with IVIg resulted in significantly lower histological grades in rat EAN. The current study provides evidence that human IVIg is effective in the treatment of EAN in the rat, indicating that this model may facilitate further investigation of the mechanism(s) of action of IVIg in inflammatory demyelinating neuropathies.

From bench to bedside--experimental rationale for immune-specific therapies in the inflamed peripheral nerve

Guillain-Barré syndrome and chronic inflammatory demyelinating polyradiculoneuropathy are autoimmune-mediated inflammatory diseases of the PNS. In recent years, substantial progress has been made towards understanding the immune mechanisms that underlie these conditions, in large part through the study of experimental models. Here, we review the available animal models that partially mimic human Guillain-Barré syndrome and chronic inflammatory demyelinating polyneuropathy, and discuss the wide range of therapeutic approaches that have been successfully established in these models of inflammatory neuropathies. Transfer of this preclinical knowledge to patients has been far less successful, and inflammatory neuropathies are still associated with significant morbidity and mortality. We will summarize successful therapeutic trials in human autoimmune neuropathies to provide a vantage point for the transfer of experimental treatment strategies to clinical practice in immune-mediated diseases of the peripheral nerve.

Immune circuitry in the peripheral nervous system

PURPOSE OF REVIEW

The aim of this review is to describe the local immune circuitry in the peripheral nervous system and its dialogue with systemic immunity under pathological conditions. Specifically, interactions of the immune system with cellular and extracellular components within peripheral nerve and immune functions of tissue-resident endoneurial macrophages and Schwann cells will be discussed.

RECENT FINDINGS

New insights into the elements involved in the pathogenesis of immune-mediated disorders of the peripheral nervous system provide a better understanding of the complex interplay of these cellular and molecular components in the immunology of the peripheral nervous system.

SUMMARY

The application of innovative and cutting-edge technologies to the study of immunoinflammatory disorders of the peripheral nervous system provides a better understanding of underlying principles of the organization of the immune network present in the peripheral nerve and its dialogue with the systemic immune system. This may foster the development of specific and highly effective therapies for immune-mediated disorders of the peripheral nerve.

An experimental model of peripheral neuropathy induced in rats by Karwinskia humboldtiana (buckthorn) fruit

Intoxication by Karwinskia humboldtiana (buckthorn) fruit presents a neurological picture similar to that of Guillain-Barré syndrome. In this report, we describe an experimental animal model of peripheral neuropathy induced by buckthorn fruit. Four groups of Wistar rats received one oral dose of 1.5 g/kg followed by oral doses of 0.5 g/kg at days 3, 7, 10, and 14 of dried and ground buckthorn fruit in aqueous suspension. Rats were sacrificed at 24, 48, 58, and 112 days after initial dose. Treated animals developed progressive paralysis through 58 days, then completely recovered by 112 days. Sciatic nerves showed segmental demyelination and cellular infiltrates until 58 days after exposure and then remyelinating changes at 112 days. This experimental model for peripheral neuropathy is reproducible and easy to handle. Its manipulation is relatively innocuous and allows us to study reversible peripheral nerve damage. This model can be developed in other animal species and may be useful to test new therapies for peripheral neuropathy.

Immunolocalization and activation of nuclear factor-κB in the sciatic nerves of rats with experimental autoimmune neuritis

Recent data support an important role played by nuclear factor kappa B (NF-kappaB) in peripheral neuropathies. We investigated expression and activation of NF-kappaB in experimental autoimmune neuritis (EAN) in rat sciatic nerves removed after 7, 14 and 21 days after immunization. Immunoreactivity for the activated form of NF-kappaB was found in the nuclei of T cells and macrophages at days 14 and 21, and also in the nuclei of few Schwann cells and of vascular endothelial cells at all time points, especially during the peak stage. Western blot showed a single band corresponding to 65 kDa in all EAN animals. NF-kappaB DNA-binding activity was revealed by electrophoretic mobility shift assay. Our results support NF-kappaB activation in EAN during the induction stage as well as in the disease remission.

Pathogenesis of chronic inflammatory demyelinating polyradiculoneuropathy

The acute lesions of chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) consist of endoneurial foci of chemokine and chemokine receptor expression and T cell and macrophage activation. The myelin protein antigens, P2, P0, and PMP22, each induce experimental autoimmune neuritis in rodent models and might be autoantigens in CIDP. The strongest evidence incriminates P0, to which antibodies have been found in 20% of cases. Failure of regulatory T-cell mechanism is thought to underlie persistent or recurrent disease, differentiating CIDP from the acute inflammatory demyelinating polyradiculoneuropathy form of Guillain-Barré syndrome. Corticosteroids, intravenous immunoglobulin and plasma exchange each provide short term benefit but the possible long-term benefits of immunosuppressive drugs have yet to be confirmed in randomised, controlled trials.

Distinct effector mechanisms in the development of autoimmune neuropathy versus diabetes in nonobese diabetic mice

NOD mice deficient for the costimulatory molecule B7-2 (NOD-B7-2KO mice) are protected from autoimmune diabetes but develop a spontaneous autoimmune peripheral neuropathy that resembles human diseases Guillain-Barre syndrome and chronic inflammatory demyelinating polyradiculoneuropathy. Similar observations have now been made in conventional NOD mice. We have shown previously that this disease was mediated by autoreactive T cells inducing demyelination in the peripheral nervous system. In this study, we analyzed the molecular pathways involved in the disease. Our data showed that neuropathy developed in the absence of perforin or fas, suggesting that classic cytotoxicity pathways were dispensable for nerve damage in NOD-B7-2KO mice. In contrast, IFN-gamma played an obligatory role in the development of neuropathy as demonstrated by the complete protection from disease and infiltration in the nerves in NOD-B7-2KO mice deficient for IFN-gamma. This result was consistent with the inflammatory phenotype of T cells infiltrating the peripheral nerves. Importantly, the relative role of perforin, fas, and IFN-gamma appears completely different in autoimmune diabetes vs neuropathy. Thus, there are sharp contrasts in the pathogenesis of autoimmune diseases targeting different tissues in the same NOD background.

[Autoimmune neuropathies--current aspects of immunopathologic diagnostics and therapy]

The group of autoimmune neuropathies includes the Guillain-Barré syndrome, chronic inflammatory demyelinating polyneuritis, multifocal motor neuropathy, neuropathies associated with monoclonal gammopathies, and vasculitic neuropathies. This educational review first addresses diagnostic pathways that facilitate more rational diagnostic decisions. Many therapies are effective for treating immune neuropathies. Unfortunately, none of the available therapies are specific. In the acute phase, glucocorticosteroids, plasmapheresis, and intravenous immunoglobulins play key roles. The list of long-term therapies includes azathioprine, cyclosporine, cyclophosphamide, and immunoglobulins. The therapeutic mechanisms involved are not clear for most of these compounds. Modern immunotherapy has to consider medical aspects, available therapeutic evidence, and long-term economic burden.

A rat model of slow Wallerian degeneration (WldS) with improved preservation of neuromuscular synapses

The slow Wallerian degeneration phenotype, Wld(S), which delays Wallerian degeneration and axon pathology for several weeks, has so far been studied only in mice. A rat model would have several advantages. First, rats model some human disorders better than mice. Second, the larger body size of rats facilitates more complex surgical manipulations. Third, rats provide a greater yield of tissue for primary culture and biochemical investigations. We generated transgenic Wld(S) rats expressing the Ube4b/Nmnat1 chimeric gene in the central and peripheral nervous system. As in Wld(S) mice, their axons survive up to 3 weeks after transection and remain functional for at least 1 week. Protection of axotomized nerve terminals is stronger than in mice, particularly in one line, where 95-100% of neuromuscular junctions remained intact and functional after 5 days. Furthermore, the loss of synaptic phenotype with age was much less in rats than in mice. Thus, the slow Wallerian degeneration phenotype can be transferred to another mammalian species and synapses may be more effectively preserved after axotomy in species with longer axons.

Experimental autoimmune neuritis induces differential microglia activation in the rat spinal cord

The reactive spatial and temporal activation pattern of parenchymal spinal cord microglia was analyzed in rat experimental autoimmune neuritis (EAN). We observed a differential activation of spinal cord microglial cells. A significant increase in ED1(+) microglia predominantly located in the dorsal horn grey matter of lumbar and thoracic spinal cord levels was observed on Day 12. As revealed by morphological criteria and by staining with further activation markers [allograft inflammatory factor 1 (AIF-1), EMAPII, OX6, P2X(4)R], reactive microglia did not reach a macrophage-like state of full activation. On Day 12, a significant proliferative response could be observed, affecting all spinal cord areas and including ED1(+) microglial cells and a wide range of putative progenitor cells. Thus, in rat EAN, a reactive localized and distinct microglial activation correlating with a generalized proliferative response could be observed.

Neuroregenerative and neuroprotective actions of neuroimmunophilin compounds in traumatic and inflammatory neuropathies

FK506 (tacrolimus, Prograf is an immunosuppressant drug that also has profound neuroregenerative and neuroprotective actions independent of its immunosuppressant activity. The separation of these properties has led to the development of non-immunosuppressant derivatives that retain the neurotrophic activity. This review focuses on the peripheral nerve actions of these compounds following mechanical injury (nerve crush or transection with graft repair) and in models of inflammatory neuropathies. Whereas FK506 may be indicative for the treatment of inflammatory neuropathies where its immunosuppressive action would be advantageous, non-immunosuppressant derivatives represent a new class of potential therapeutic agents for the treatment of human neurological conditions in general. Moreover, these studies have led to the discovery of a novel mechanism whereby these compounds activate intrinsic neuroregenerative and neuroprotective pathways in the neuron.

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.