New minimum length requirement for a T cell epitope for experimental allergic neuritis

Structural and functional characterization of human peripheral nervous system myelin protein P2

The myelin sheath is a tightly packed multilayered membrane structure insulating selected axons in the central and the peripheral nervous systems. Myelin is a biochemically unique membrane, containing a specific set of proteins. In this study, we expressed and purified recombinant human myelin P2 protein and determined its crystal structure to a resolution of 1.85 A. A fatty acid molecule, modeled as palmitate based on the electron density, was bound inside the barrel-shaped protein. Solution studies using synchrotron radiation indicate that the crystal structure is similar to the structure of the protein in solution. Docking experiments using the high-resolution crystal structure identified cholesterol, one of the most abundant lipids in myelin, as a possible ligand for P2, a hypothesis that was proven by fluorescence spectroscopy. In addition, electrostatic potential surface calculations supported a structural role for P2 inside the myelin membrane. The potential membrane-binding properties of P2 and a peptide derived from its N terminus were studied. Our results provide an enhanced view into the structure and function of the P2 protein from human myelin, which is able to bind both monomeric lipids inside its cavity and membrane surfaces.

Experimental autoimmune encephalomyelitis in the rat

There are several diverse rat models of experimental autoimmune encephalomyelitis (EAE) that can be used to investigate the pathogenesis and regulation of autoimmunity against CNS myelin. The disease course of these models ranges from an acute monophasic disease with limited demyelination to a chronic relapsing or chronic progressive course marked by severe demyelination. These models enable the study of encephalitogenic T cells and demyelinating antibody specific for major neuroantigens such as myelin basic protein (MBP), myelin oligodendrocyte glycoprotein (MOG), or proteolipid protein (PLP), among other important CNS autoantigens. Overall, this unit provides an overview of common methods for induction of active and passive EAE, assessment and analysis of clinical disease, preparation and purification of myelin basic protein, and derivation of neuroantigen-specific rat T cell lines. This unit also provides a brief discussion of the basic characteristics of these models.

CD4 T cells mediate axonal damage and spinal cord motor neuron apoptosis in murine p0106-125-induced experimental autoimmune neuritis

The pathogenesis of inflammatory autoimmune diseases of the peripheral nervous system, leading to demyelination and/or axonal damage, remains incompletely understood. In particular, it is controversial regarding the extent to which (i) autoimmune-mediated destruction of peripheral nerves results in secondary damage of the central nervous system, and (ii) CD4 and CD8 T cells contribute to disease. To address these issues, we applied the murine model of P0(106-125)-induced experimental autoimmune neuritis. Immunization of C57BL/6 mice with P0(106-125) resulted in severe axonal damage and mild demyelination. Importantly, these mice developed a "dying-back" axonopathy with apoptosis of a large fraction of neurons in the anterior horn of the lumbar and thoracic spinal cord and a progressive neurogenic muscular atrophy. T cell-depletion experiments identified CD4, but not CD8, T cells as important mediators of experimental autoimmune neuritis. CD4 T cells represented the major cellular source of antigen-specific interferon-gamma and interleukin-17 production, regulated the number of tumor necrosis factor-positive and inducible nitric oxide synthase-positive macrophages in the diseased sciatic nerve, and mediated axonal damage and subsequent neuronal apoptosis and neurogenic muscular atrophy. In contrast, the demyelination of peripheral nerves was only slightly ameliorated in CD4 T cell-depleted mice. In conclusion, P0(106-125)-induced experimental autoimmune neuritis is a CD4 T cell-mediated autoimmune disease that affects both the peripheral and central nervous systems.

Antibody responses to peptides of peripheral nerve myelin proteins P0 and P2 in patients with inflammatory demyelinating neuropathy

BACKGROUND

Antibodies with reactivity to peripheral nerve myelin have previously been found in the serum, and bound to peripheral nerves of patients with Guillain-Barré syndrome (GBS) and chronic inflammatory demyelinating polyradiculoneuropathy (CIDP).

AIM

To investigate the presence of antibodies reactive to specific peptide sequences within the myelin proteins P0 and P2 in patients with GBS, in patients with CIDP, in healthy controls and in patients with other neuropathies (ON).

METHODS

Blood was obtained from 48 patients with GBS, 36 with CIDP, 48 with ON and 38 controls. ELISA was used to detect antibody responses to peptides of the human peripheral myelin proteins P0 and P2. Blood samples were collected from patients with GBS in early, peak and recovery stages of GBS to analyse antibody levels throughout the course of the disease.

RESULTS

Significantly increased total IgG levels were found in patients with GBS compared with other groups. A higher percentage of patients with GBS at the peak of disease had antibody reactivity to P2(14-25) compared with patients with CIDP and control groups. In patients with GBS and CIDP, the percentages of patients with antibody reactivity to P2(61-70), and peptides derived from P0, were comparable to the control groups. Although some individual patients with GBS had high titres of reactivity to the peptide antigens tested, most patients with GBS and CIDP had levels of antibody similar to controls.

CONCLUSION

Our data suggest that increased IgG levels and increased antibody reactivity to P2(14-25) in patients with GBS at the peak of disease may play a contributory role in the disease process in some patients with demyelinating forms of GBS.

MHC and non-MHC gene regulation of disease susceptibility and disease course in experimental inflammatory peripheral neuropathy

With a panel of rat strains, we demonstrate a strong impact of the MHC genotype on susceptibility and disease course in experimental autoimmune neuritis induced with peripheral nerve myelin or the P2 peptide 58-81 (KNTEISFKLGQEFEETTADNRKTK). Beside the MHC genotype, non-MHC genes determined disease susceptibility and resistance. The type of disease induced with P2 58-81 was strongly correlated to the strength of the MHC class II isotype interaction with P2 58-81. These findings suggest a link between susceptibility and acute versus chronic disease courses on one hand and the strength of the MHC class II molecule/peptide affinity on the other hand.

Biphasic form of experimental autoimmune neuritis in dark Agouti rats and its oral therapy by antigen-specific tolerization

A new and biphasic form of experimental autoimmune neuritis (EAN) is described in dark agouti rats (DA rats) and is inducible by a single immunization with bovine peripheral nerve myelin (BPM) in complete Freund's adjuvant (DA-EAN). Animals develop a mild episode of disease; after recovery, 66-100% of the rats suffer from a more severe bout of EAN with paraparesis 25-30 days after immunization. By histology, DA-EAN is an inflammatory and demyelinating polyradiculoneuropathy virtually without axonal damage. Demyelination affects mainly spinal roots. This is also reflected by markedly increased F-wave latencies in nerve conduction studies of sciatic nerves. In sciatic nerves, inflammation and demyelination are found only focally and may be the histopathologic basis for conduction failure in some fibers. Immunologic investigations revealed stronger proliferative responses of DA than of Lewis rat lymph node cells to BPM and various peptides derived from the P2 protein. Proliferative and Th1-cytokine responses were particularly pronounced in spleen during the late phase of DA-EAN as compared to the monophasic EAN of Lewis rats. The data suggest that persistent lymphocyte proliferation with secretion of interferon (IFN)-gamma may be relevant for the relapsing course of DA-EAN whereas epitope spreading may explain the increased severity of the second bout of disease. The extended Th1 response in DA rats did not go along with a lack of downregulatory mechanisms, because the second DA-EAN attack was self-limited and splenocytes from DA rats produced considerable amounts of interleukin (IL)-10 and transforming growth factor (TGF)-beta. To substantiate further a functional immunoregulation in DA rats, we modulated DA-EAN by antigen-specific oral tolerization, which is known to involve active suppressor mechanisms. Preventive feeding of BPM in combination with cholera toxin (CT) induced a long-lasting resistance to DA-EAN. Even therapeutic administration of BPM or BPM/CT after onset of signs of disease significantly mitigated the further course of disease and prevented development of paraparesis. Because DA-EAN is easily inducible and leads consistently to relapses in most rats, it can be used for studies of immune factors that determine a relapsing course of autoimmunity. Furthermore, DA-EAN may serve as a model for relapsing inflammatory demyelinating polyneuropathies such as chronic inflammatory demyelinating polyneuropathy (CIDP) and for treatment studies. Our findings on effective prevention and therapy of DA-EAN by oral application of myelin/CT corroborate this form of immunomodulation as a treatment strategy for cell-mediated processes in chronic inflammatory neuropathies.

Inflammation and proinflammatory cytokine production, but no demyelination of facial nerves, in experimental autoimmune neuritis in Lewis rats

Experimental autoimmune neuritis (EAN) is a CD4(+) T cell-mediated, inflammatory demyelinating disease of the peripheral nervous system (PNS) that serves as a model for Guillain-Barré syndrome (GBS) in humans. The facial nerve paralysis is relatively commonly found in GBS patients. Here, EAN was established in Lewis rats by immunization with P2 peptide 57-81, a purified component of peripheral nerve myelin, and Freund's complete adjuvant (FCA). To study whether the facial nerves are involved in the pathogenic process during the EAN course, we observed the clinical and pathological changes as well as cytokine production in facial nerves on Day 14 postimmunization (p.i.), i.e. at height of clinical EAN. As a result, all rats immunized with P2 peptide 57-81 developed severe EAN on Day 14 p.i., but none of the rats manifested clinical signs of facial nerve paralysis. Additionally, only mild inflammatory cell infiltration and proinflammatory cytokine, interferon-gamma (IFN-gamma) and tumour necrosis factor (TNF-alpha) production as well as devoid demyelination were seen in facial nerves of the EAN rats. On the contrary, severe inflammation and demyelination as well as upregulated IFN-gamma and TNF-alpha production were observed in sciatic nerves of the same EAN rats. The underlying mechanism for the difference of the local manifestation of the disease process of EAN remains to be resolved.

Animal models of immune-mediated neuropathies

PURPOSE OF REVIEW

This article gives an overview on animal models for immune-mediated demyelinating disorders of the peripheral nervous system. As insight into human disease is mainly based on biopsy material and ex-vivo analysis, an understanding of the pathogenetic mechanism of these complex and heterogeneous disorders is mainly based on animal models.

RECENT FINDINGS

Besides experimental autoimmune neuritis in rats, recent efforts to establish this model in mice are discussed. In addition, models for spontaneous autoimmune neuropathies and secondary immune reactions in degenerative disorders of the peripheral nervous system are reviewed.

SUMMARY

Recently described animal models offer the possibility to analyse the complex interaction of genetic and immunological factors. The entire panel of animal models for immune-mediated disorders of the peripheral nervous system provides a rational basis for studying the mechanisms of pathogenesis and new immunotherapeutic strategies for human autoimmune demyelinating neuropathies.

Truncation of the neuritogenic peptide bP2(60-70) results in the generation of altered peptide ligands with the potential to interfere with T cell activation

Due to the central role of T cells in the pathogenesis of inflammatory diseases of the peripheral nervous system like the Guillain-Barré syndrome, specific immunotherapies aim at modifying T cell responses. Use of truncated mutants of the neuritogenic peptide of myelin basic protein (MBP) has been shown to anergize autoreactive T cells and to reverse experimental autoimmune encephalitis (EAE). To establish a rationale basis for the use of altered peptide ligands (APLs) in the treatment of autoimmune diseases we designed a set of N- and C-terminally truncated mutants of the minimal experimental autoimmune neuritis (EAN) inducing bovine P2 (bP2) (60-70) peptide and compared them for the ability to induce immune responses and T cell receptor (TCR) cell signaling. Truncated peptides bound to MHC class II molecules and induced TCR internalization and expression of interferon gamma (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha) with decreasing potency. None of the shortened mutants elicited a proliferative response in P2-specific T cells. Stimulation of these antigen-specific T cells with peptide bP2(62-69) using antigen presenting cells (APCs) prepulsed with bP2(60-70) resulted in a significant decrease of the proliferative response. In agreement with the observed effects on T cell activation, analysis of TCR signaling demonstrated a lack of CD3 epsilon phosphorylation and MAPK activation. Moreover, repeated injection of bP2(62-69) significantly slowed progression of adoptive transfer EAN (AT-EAN). Taken together, these findings strongly suggest that peptide bP2(62-69) can favorably modulate the antigen-induced response of neuritogenic T cells.

Immune mechanisms in acquired demyelinating neuropathies: lessons from animal models

The peripheral nervous system (PNS) is the target for a heterogenous immune attack mediated by T-cells, B-cells, and macrophages. The interaction of the humoral and cellular immune system with the structural components in the peripheral nervous system may determine the extent of inflammation and possibly repair mechanisms. The animal model experimental autoimmune neuritis (EAN) allows detailed study of the various effector pathways and tests novel therapeutic strategies in vivo. Unexpectedly, involvement of the immune system is also found in animal models for inherited neuropathies and in its human counterpart Charcot-Marie-Tooth (CMT) disease, suggesting an autoimmune reaction triggered by the genetically determined demyelinating disorder. A better understanding of immune regulation and its failure in the peripheral nervous system may help to develop more specific and more effective immunotherapies.

Initiation and development of experimental autoimmune neuritis in Lewis rats is independent of the cytotoxic capacity of NKR-P1A+ cells

Natural killer (NK) cells are implicated in T cell-mediated autoimmune diseases. Experimental autoimmune neuritis (EAN) is a CD4+ T cell-mediated animal model of the Guillain-Barré syndrome in human. The role of NK cells in the initiation and development of EAN remains unclear. In the present study, we demonstrate that anti-NKR-P1A monoclonal antibody (mAb) treatment in vivo did not affect the initiation and development of clinical EAN in Lewis rats induced by immunization with peripheral nerve myelin P0 protein peptide 180-199 and Freund's complete adjuvant, as well as the proportion of NKR-P1A+ cells (including NK cells and NKT cells) in the spleen. Furthermore, inflammatory cell infiltrations and demyelination in the peripheral nervous system (PNS) and in vitro P0 peptide 180-199-specific splenocyte proliferation were not different in anti-NKR-P1A mAb-treated rats compared to the control antibody-treated rats. The cytotoxic activity of NKR-P1A+ cells, determined by NK cell-sensitive K562 cells as target cells, decreased markedly in anti-NKR-P1A mAb-treated rats, suggesting that decrease of the cytotoxic activities of NKR-P1A+ cells is not sufficient to alter clinical EAN, although NKR-P1A+ cells may participate in the pathogenesis of T cell-mediated autoimmune diseases, such as EAN, by the mechanisms that involve the release of cytokines.

Vaccination, prevention, and treatment of experimental autoimmune neuritis (EAN) by an oligomerized T cell epitope

Using a polypeptide oligomer harboring 16 repeats of the neuritogenic epitope (aa 58-73) of myelin P2 protein separated by spacers, enhancement of the immune response to the P2 protein, an important neuritogenic autoantigen in experimental autoimmune neuritis (EAN), was attempted. In contrast to a previous study with PLP-16-mer antigen-specific response of T cells was attenuated at all doses examined to a variable degree. Treatment of Lewis rats with the P2-16-mer up to 2 months before immunization with P2(53-78) (vaccination) or after immunization but before appearance of disease (prevention) had a strong tolerizing effect against the induction of EAN on immunization with P2(53-78). Moreover, rats injected with 200 microg of the P2-16-mer i.v. on day 11 after disease induction, at which time the initial signs of disease had appeared, were almost completely protected against progression of clinical disease, whereas animals treated with the same amount of monomeric control peptide developed severe disease (treatment). Similar results were obtained by i.v. treatment of adoptive-transfer EAN with the P2-16-mer. The lack of clinical signs of disease after 16-mer therapy could be correlated with a reduced proliferative response of P2(53-78)-specific lymph node cells. The frequency of apoptotic T cells in sciatic nerve or in lymph node cells, however, was not increased by the 16-mer treatment, suggesting that induction of anergy or other forms of peripheral tolerance may be responsible for the effect. Thus, the oligomerized P2 peptide antigen was highly effective in all three treatment modalities examined in this specific autoreactive T cell-mediated immune response.

P0 glycoprotein peptides 56-71 and 180-199 dose-dependently induce acute and chronic experimental autoimmune neuritis in Lewis rats associated with epitope spreading

Two synthetic peripheral nerve myelin P0 protein peptides, an immunodominant (amino acids 180-199) and a cryptic (amino acids 56-71) one, induced an acute or chronic course of experimental autoimmune neuritis (EAN) in Lewis rats, when given at low dose (50-100 microg/rat) or high dose (250 microg/rat), respectively. Corresponding to the different clinical course, pathological changes and immune responses were found: (1) Onset of clinical signs of P0 peptide 56-71 (P0 56-71) induced EAN was 1-3 days later than in P0 peptide 180-199 (P0 180-199) induced EAN at all immunizing doses, whereas the peak of the disease occurred at a similar time point post immunization (p.i.), i.e. at days 14-16 p.i. in P0 56-71 induced EAN and at day 16 p.i. in P0 180-199 induced EAN. (2) Intramolecular epitope spreading as assessed by delayed type hypersensitivity response occurred in P0 56-71 induced EAN at both low and high antigen doses and in P0 180-199 induced EAN at high antigen dose (250 microg/rat) only. (3) P0 180-199 stimulated higher levels of interferon-gamma production in P0 180-199 induced EAN than in P0 56-71 induced EAN and vice versa. (4) Histopathologic evaluation revealed a similar grade of mononuclear cell infiltration in the sciatic nerves of both types of EAN, but more severe demyelination was found in P0 180-199 induced EAN compared to P0 56-71 induced EAN. The results support the hypothesis that high dose autoantigen immunization induces extensive determinant spreading and chronic course of autoimmune diseases.

Lipid-free versus lipid-bound P2 protein-induced experimental allergic neuritis: clinicopathological, neurophysiological, and immunological study

The P2 protein of the peripheral nervous system myelin is a neuritogenic protein capable of inducing experimental allergic neuritis (EAN) in the Lewis rat. It has been suggested that the addition of some lipids to the protein isolated in the lipid-free form might enhance its immunogenicity. In this study, we compared lipid-free P2 (the EAN factor) and the corresponding lipid-bound form of the protein regarding their ability to induce EAN. Lipid-bound P2, copurified with all the myelin lipids, shows a conformation different from that of LF-P2. The timing of disease and the clinical scores of lipid-bound P2-induced EAN animals (n = 23) did not differ statistically from those injected with lipid-free P2 (n = 23), with only a tendency to higher clinical severity in the former group. Tail nerve conduction velocities did not differ in the two groups and in both were significantly lower in comparison to Freund adjuvant controls (n = 8). Inflammation and demyelination predominated in the spinal roots and were less evident in the sciatic nerve for both groups of animals. The ELISA determination of antibodies to lipid-free and lipid-bound P2 revealed the development of antibodies recognizing the lipid-free form of the protein in both groups of animals. Our results stand in contrast to results of previous studies performed after addition of exogenous lipids to the P2 purified in the lipid-free form and indicate that lipid-bound P2 is not significantly more immunogenic than lipid-depleted P2.

A Complementary Peptide Vaccine That Induces T Cell Anergy and Prevents Experimental Allergic Neuritis in Lewis Rats

We have developed and described a new method of altering T cell-mediated autoimmune diseases by immunization with the complementary peptide against T cell epitopes. The complementary peptide (denoted NAE 07-06) to the bovine P2 protein, residues 60–70 (denoted EAN 60–70), was tested in the Lewis rat model of experimental allergic neuritis (EAN). Immunization with NAE 07-06 induced polyclonal and monoclonal Abs that inhibited the proliferation of the P2-specific T cell line, stimulated with EAN 60–70, and recognized Vβ, but not Vα, of TCRs. Proliferation of T cells treated with anti-NAE 07-06 Abs could be partially restored by treatment with rIL-2, in accordance with an anergy model. A homologous sequence was found between NAE 07-06 and the VDJ junction of the TCR β-chain from an EAN 60–70-specific T cell line. Rats preimmunized with NAE 07-06 in vivo before EAN induction showed less disease severity clinically and histologically. These data suggest a new therapeutic approach for T cell-mediated autoimmune disorders through the induction of anti-TCR Abs with complementary peptide Ags.

Suppression of chronic experimental autoimmune neuritis by nasally administered recombinant rat interleukin-6

Experimental autoimmune neuritis (EAN) is a CD4+ T-cell-mediated demyelinating disease of the peripheral nervous system (PNS) and serves as experimental model for human immune-demyelinating neurophathies, especially the Guillain-Barré syndrome. In this study, we examined the effect of recombinant rat interleukin-6 (rrIL-6) on chronic EAN in Lewis rats induced by immunization with P2 peptide 57-81 and Freund's complete adjuvant (FCA). Nasal administration of rat rIL-6 (1 microg/rat/day) beginning in the initial phase of EAN as a therapeutic agent, decreased the severity and the duration of clinical EAN. Low-grade inflammation and suppression of regional demyelination within the sciatic nerves were seen in rrIL-6-treated rats. Hyporesponsiveness of lymph node T cells, down-regulation of serum tumour necrosis factor-alpha (TNF-alpha) and increased levels of P2-specific immunoglobulin G1 (IgG1) antibodies document that nasal administration of rrIL-6 was effective systemically. However, because of the non-specific nature of the treatment and multiple effects of IL-6, more experience and great caution are needed, before nasal administration of IL-6 can be considered as a treatment of human autoimmune demyelinating neurophathies.

Induction of experimental autoimmune neuritis in CD4-8-C57BL/6J mice

The C57BL/6J mice strain is known to be reputedly resistant to induction of experimental autoimmune neuritis (EAN), an animal model of Guillain-Barré syndrome in humans. Here we describe the induction of EAN in mice of the C57BL/6J background by transfer into naive syngeneic recipients bovine peripheral nerve myelin (BPM)-primed donor lymph node cells that had been stimulated in vitro with the bovine peripheral nervous system (PNS) myelin P2 protein peptide 57-81 followed by challenge with BPM, Freund's complete adjuvant and pertussis toxin. EAN was more severe, both clinically and histologically, and accompanied by extensive infiltration of inflammatory cells and demyelination in peripheral nerves when examined on day 30 after transfer of primed T cells from CD4- 8- mice into identical naive hosts than after transfer of cells from primed wild type, CD4-/- or CD8-/- mice to corresponding recipient animals. EAN in CD4-8- mice was also associated with elevated numbers of P2 peptide-reactive interferon-y (TFN-gamma) secreting cells and alphabeta T cells were present in lymph nodes and spleens. The data suggest that PNS myelin activated T cells from an EAN-resistant mice strain are capable of homing to the PNS. The expanded CD4-8- alphabeta T cells may have helper and effector functions, related to initiation of EAN in the CD4-8- mice. Lack of CD4+ and CD8+ expressing cells does not prevent the initiation of an autoimmune disease.

Treatment with P2 protein peptide 57-81 by nasal route is effective in Lewis rat experimental autoimmune neuritis

Experimental autoimmune neuritis (EAN) is a CD4+ T cell-mediated autoimmune disorder of the peripheral nervous system (PNS) that can be actively induced in susceptible animal species and strains by active immunization with PNS myelin + Freund's complete adjuvant (FCA). EAN represents an animal model for studying the immunopathogenesis and treatment of Guillain-Barré syndrome (GBS), which is a major inflammatory demyelinating disease of the PNS in humans. Here, we report that treatment by nasal administration of the neuritogenic peptide 57-81 of the PNS myelin component, P2 protein, dose-dependently suppressed EAN severity and shortened clinical EAN. Clinical EAN relapse induced by rechallenge with BPM + FCA was also prevented in EAN rats receiving high dose P2 peptide. P2 peptide induced suppression of EAN was associated with PNS antigen specific T cell hyporesponsiveness reflected by lymphocyte proliferation, numbers of PNS antigen-reactive IFN-gamma secreting and IFN-gamma mRNA expressing lymph node cells, but elevated levels of PNS antigen reactive TGF-beta mRNA secreting cells. Reduced CD4+ T cell and macrophage infiltrations within the PNS were also observed. Based on these observations, nasal autoantigen administration should be further evaluated, considering its possible future use in GBS.

Human autoimmune neuropathies

Peripheral nerve diseases are among the most prevalent disorders of the nervous system. Because of the accessibility of the peripheral nervous system (PNS) to direct physiological and pathological study, neuropathies have traditionally played a unique role in developing our understanding of basic mechanism of nervous system injury and repair. At present they are providing new insight into the mechanisms of immune injury to the nervous system. A rapidly growing catalogue of PNS disorders are now suspected to be immune-mediated, and in the best understood of these disorders, the molecular and cellular targets of immune attack are known, and the pathophysiology follows directly from the specific immune injury. This review summarizes the immunologically relevant features of the PNS, then considers selected immune-mediated neuropathies, focusing on pathogenetic mechanisms. Finally, the PNS is providing a testing ground for new immunotherapies and approaches to protection and regeneration, including the use of trophic factors. The current status of treatment and implications for future approaches is reviewed.

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.

Cytokine dichotomy in peripheral nervous system influences the outcome of experimental allergic neuritis: dynamics of mRNA expression for IL-1 beta, IL-6, IL-10, IL-12, TNF-alpha, TNF-beta, and cytolysin

Experimental autoimmune neuritis (EAN) is a T-cell-mediated autoimmune disease of the peripheral nervous system (PNS) that can be actively induced in Lewis rats by immunization with bovine PNS myelin and Freund's complete adjuvant. EAN is used as an animal model of the Guillain-Barré syndrome (GBS) in humans. To study the potential role of cytokines in EAN, we used in situ hybridization to detect mRNA expression of interleukin 1 beta (IL-1 beta), IL-6, IL-10, IL-12, tumor necrosis factor-alpha (TNF-alpha), TNF-beta, and cytolysin in sciatic nerve sections over the course of EAN. Cells expressing IL-1 beta and IL-6 mRNA appeared early and peaked on Day 7 postimmunization (p.i.), i.e., at onset of clinical signs of EAN, consistent with a role of these cytokine in an early immune response leading to autoaggressive immunity in EAN. TNF-alpha, TNF-beta, and IL-12 mRNA expression was maximally upmodulated on Day 14 p.i., i.e., at height of clinical EAN, favoring a role for these cytokines in disease development. On the contrary, transcription of cytolysin and IL-10 in sciatic nerves reached maxima during clinical improvement of EAN. The data argue for a major proinflammatory role for IL-1 beta, IL-6, TNF-alpha, TNF-beta, and IL-12 and a disease downregulating function for both cytolysin and IL-10 at the target site in EAN. These findings have relevance for future studies on pathogenesis and treatment of GBS in humans.

IL-10 suppresses experimental autoimmune neuritis and down-regulates TH1-type immune responses

Experimental autoimmune neuritis (EAN) is a CD4+ T cell-mediated monophasic inflammatory disorder of the peripheral nervous system (PNS). Cellular mechanisms, including macrophage and T cell infiltration, and cytokines like IFN-gamma and TNF-alpha are intimately involved in the pathogenesis of EAN. Interleukin 10 (IL-10) is a TH2-type cytokine that suppresses monocyte and TH1 cell functions. We examined the effect of recombinant human IL-10 (rHuIL-10) in EAN. When administered from the start of immunization with bovine peripheral myelin emulsified in Freund's complete adjuvant, IL-10 effectively suppressed and shortened clinical EAN. Even when given after Day 12 post immunization (pi) after clinical EAN had been established, IL-10 also effectively suppressed the severity of EAN. Pheripheral nerve myelin antigen-reactive IFN-gamma-secreting TH1-like cells were decreased in lymph nodes from IL-10-treated compared to control EAN rats. PNS autoantigen-induced T cell proliferation and B cell responses were not affected. P2 protein-reactive IFN-gamma, TNF-alpha, IL-1 beta, and IL-6 mRNA-expressing lymph node cells were also downregulated in IL-10-treated compared to control EAN rats at Day 14 and 26 pi, while P2-reactive IL-4 mRNA-expressing cells were upregulated throughout treatment. Also, in IL-10-treated EAN rats, upregulated anti-P2 IgG1 and downregulated IgG2a were observed. Our results clearly show that rHuIL-10 can suppress clinical EAN, and this suppression is associated with downregulation of TH1 responses and macrophage function and upregulated TH2 responses.

Antigalactocerebroside antibody increases demyelination in adoptive transfer experimental allergic neuritis

There is suggestive but inconclusive evidence for a contribution of T cells and antimyelin antibodies to the pathogenesis of the Guillain-Barré polyneuropathy. We have studied the potential synergism of cellular and humoral immunity in the adoptive transfer model of EAN. EAN was induced in Lewis rats by injecting varying doses of P2 peptide (SP26)-sensitized T lymphocytes. Disease severity was dose-dependent. The addition of intravenous GC-AB to a subclinical dose of SP26-sensitized T cells resulted in overt clinical disease and markedly enhanced demyelination. Intravenous injection of antibody alone had no effect. We conclude that activated neuritogenic T cells, while entering into peripheral nerves, alter the blood-nerve barrier, which gives circulating demyelinating antibodies access to the endoneurium. The observations support the concept of a synergistic role of T-cell autoimmunity and humoral responses in the inflammatory demyelination of Lewis rat EAN.

Adoptive transfer of experimental allergic neuritis in the immune suppressed host

Experimental allergic neuritis (EAN) was induced in normal and irradiated Lewis rats by passively transferring T cells sensitized to SP-26, a peptide fragment of P2 myelin protein. The recipients became sick 4-8 days post transfer and the degree of disability correlated directly with the dose of T cells. Smaller doses caused demyelination of nerve roots and sciatic nerves and larger doses produced more severe demyelination and significant axonal degeneration. Irradiated recipients developed similar clinical EAN and showed macrophage-mediated demyelination despite severe suppression of the host inflammatory response.

Antibody responses to P0 and P2 myelin proteins in Guillain-Barré syndrome and chronic idiopathic demyelinating polyradiculoneuropathy

Immunisation with the peripheral nerve myelin proteins P0 or P2 induces inflammatory neuropathy in animals. We sought antibodies with an ELISA to these proteins in 38 patients with acute Guillain-Barré syndrome (GBS), 32 patients with chronic idiopathic demyelinating polyradiculoneuropathy (CIDP), 31 patients with other neuropathies (ONP) and 26 normal control (NC) subjects. We discovered IgM antibodies to human P0 protein in the sera of 18.5% of the patients with GBS, 15.6% with CIDP, 6.4% with ONP and 3.8% of NC subjects. Of the sera which reacted with P0, sera from 4/7 of GBS, 3/5 of CIDP, 1/2 of ONP patients and 0/1 of NC subjects reacted with a synthetic P0 peptide representing residues 150-169 from the cytoplasmic portion of the molecule. IgG antibodies to P0 were slightly less common than IgM antibodies, being present in only 7.9% of GBS, 0% of CIDP and 3% of ONP patients and 0% of NC subjects. We found antibodies to bovine P2 protein more commonly than antibodies to P0. IgM antibodies were present in 39.5% of GBS, 34.4% of CIDP, 16.1% of ONP patients and 15.4% of NC subjects. IgG antibodies were present in 18.4% of GBS, 12.5% of CIDP, 3.2% of ONP patients and 7.6% of NCs. Of the sera which contained antibodies to P2 protein, only a few reacted with P2 peptides 14-25 or 58-81, but without any consistent pattern of reactivity.(ABSTRACT TRUNCATED AT 250 WORDS)

Peripheral nervous system (PNS) expression of mRNAs encoding myelin proteins and Fc gamma RIII during experimental allergic neuritis

Experimental allergic neuritis (EAN) was induced in Lewis rats by injection of 'SP26', a peptide homologous to amino acids 53-78 of bovine myelin P2 protein, in complete Freund's adjuvant. The rats developed signs of EAN which began on day 14, were maximal on day 18, and had subsided by day 30. RNA content of cauda equina and sciatic nerves increased more than 2-fold at the height of EAN. Expression of myelin P0 and P1 mRNAs did not fall during EAN, nor rise during recovery. Fc gamma R mRNA, which encodes Fc gamma RIII, an immunoglobulin-binding protein mediating activation of natural killer cells and macrophages by immune complexes, was transiently, but markedly induced in scattered endoneural cells, presumably macrophages, in cauda equina and sciatic nerves during the period of increasing weakness.

T cell responses to myelin proteins in Guillain-Barré syndrome

We have investigated the hypothesis that the pathogenesis of Guillain-Barré syndrome (GBS) involves an autoimmune T cell response to P0 and P2 proteins of peripheral nerve myelin. The proliferative responses of blood mononuclear cells (MNC) to myelin proteins and synthetic peptides derived from them were determined in patients with GBS and chronic idiopathic demyelinating polyradiculoneuropathy (CIDP), normal controls (NC) and patients with other neuropathies (ONP). Twelve out of 19 GBS patients responded to P0 or P2, 6 to P0 and its peptides only, 3 to P2 and its peptides only, and 3 to both P0 and P2 antigens. Responses to at least one of the antigens were also found in 6/13 of CIDP patients, but in only 4/17 NC and 2/6 ONP. Immune responses in GBS are heterogeneous. The early T cell responses to P0 protein, described here for the first time, may be important in the pathogenesis of some cases.

Experimental allergic neuritis in the SJL/J mouse: dysfunction of peripheral nerve without clinical signs

Experimental allergic neuritis (EAN) was studied in the SJL/J mouse and compared to EAN in the Lewis rat. The Lewis rat developed hind limb weakness and weight loss while the SJL/J mouse had no discernible clinical abnormalities. The SJL/J mouse, however, suffered subclinical damage to peripheral nerve (PN) myelin. Both species reproducibly developed electrophysiologic dysfunction of PN and histopathology confined to the peripheral nervous system (PNS). Understanding of autoimmune demyelination in the central nervous system was greatly enhanced by the development of experimental allergic encephalomyelitis in the SJL/J mouse. We believe that EAN in the SJL/J mouse could lead to a similar increase in our understanding of autoimmune demyelination in the PNS.

P2-peptide induced experimental allergic neuritis: a model to study axonal degeneration

In experimental allergic neuritis (EAN) severity of clinical disease and pathology correlate with the dose of antigen (Hahn et al., Lab Invest 59:115-125, 1988). To avoid axonal membrane contamination of the antigen, EAN was induced with a synthetic peptide, corresponding to residues 53-78 of bovine P2 myelin protein. Severity of EAN correlated with the dose of peptide in the inoculate. The relationship between demyelination, inflammation and axonal degeneration was studied. Low doses resulted in pure demyelination. Axonal degeneration occurred only with high doses of antigen and in association with very active mononuclear inflammation. The role of macrophages in producing axonal damage is discussed.

Response of the axon and barrier endothelium to experimental allergic neuritis induced by autoreactive T cell lines

Experimental allergic neuritis was induced in Lewis rats by inoculation with autoreactive T cell lines sensitized to residue 57-81 of P2 myelin protein. Control rats received cells derived from immunization to complete Freund's adjuvant alone. Endoneurial fluid pressure (EFP) was measured in both sciatic nerves at 0, 3, 5, 7, 9, and 11 days post-inoculation (PI). The temporal evolution of inflammatory disease was studied by correlating EFP with a morphometric analysis of the nerve microenvironment and with electron microscopic observations. Both edema, as evidenced by increased endoneurial extracellular space, and inflammation paralleled the time course of the EFP increase, reaching peak values at 7 days PI and declining to near-normal values after 11 days. Wallerian degeneration was detectable at 7 days and increased 9 days after inoculation. Axonal damage appeared at the height of the inflammatory process, when edema and increased EFP were maximal. Evidence of demyelination was apparent by 7 days and persisted through 11 days. The onset of edema was associated with changes in venular endothelial cells which tended to lose their normal scaphoid appearance and assumed rhomboid configurations reminiscent of high endothelial venules. At that point, the barrier endothelium was visibly disrupted with the loss of tight junctions and separation of adjacent cells. Specific cell-cell interactions took place between endothelial cells and infiltrating leukocytes as they immigrated into the endoneurial compartment. There was evidence of altered perineurial permeability with fibrin deposition and leukocyte infiltration between the layers of the perineurial sheath.