Inhibition of chronic relapsing experimental allergic encephalomyelitis in the Biozzi AB/H mouse

Complement activation and expression during chronic relapsing experimental autoimmune encephalomyelitis in the Biozzi ABH mouse

Chronic relapsing experimental autoimmune encephalomyelitis (crEAE) in mice recapitulates many of the clinical and histopathological features of human multiple sclerosis (MS), making it a preferred model for the disease. In both, adaptive immunity and anti-myelin T cells responses are thought to be important, while in MS a role for innate immunity and complement has emerged. Here we sought to test whether complement is activated in crEAE and important for disease. Disease was induced in Biozzi ABH mice that were terminated at different stages of the disease to assess complement activation and local complement expression in the central nervous system. Complement activation products were abundant in all spinal cord areas examined in acute disease during relapse and in the progressive phase, but were absent in early disease remission, despite significant residual clinical disease. Local expression of C1q and C3 was increased at all stages of disease, while C9 expression was increased only in acute disease; expression of the complement regulators CD55, complement receptor 1-related gene/protein y (Crry) and CD59a was reduced at all stages of the disease compared to naive controls. These data show that complement is activated in the central nervous system in the model and suggest that it is a suitable candidate for exploring whether anti-complement agents might be of benefit in MS.

Experimental autoimmune encephalomyelitis is a good model of multiple sclerosis if used wisely

Although multiple sclerosis is a uniquely human disease, many pathological features can be induced in experimental autoimmune encephalomyelitis (EAE) models following induction of central nervous system-directed autoimmunity. Whilst it is an imperfect set of models, EAE can be used to identify pathogenic mechanisms and therapeutics. However, the failure to translate many treatments from EAE into human benefit has led some to question the validity of the EAE model. Whilst differences in biology between humans and other species may account for this, it is suggested here that the failure to translate may be considerably influenced by human activity. Basic science contributes to failings in aspects of experimental design and over-interpretation of results and lack of transparency and reproducibility of the studies. Importantly issues in trial design by neurologists and other actions of the pharmaceutical industry destine therapeutics to failure and terminate basic science projects. However animal, particularly mechanism-orientated, studies have increasingly identified useful treatments and provided mechanistic ideas on which most hypothesis-led clinical research is based. Without EAE and other animal studies, clinical investigations will continue to be "look-see" exercises, which will most likely provide more misses than hits and will fail the people with MS that they aim to serve.

Immunosuppression with FTY720 is insufficient to prevent secondary progressive neurodegeneration in experimental autoimmune encephalomyelitis

BACKGROUND

There has been poor translation for the use of immunosuppressive agents from experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS), into the treatment of MS. This may be due to the fact that most EAE studies examine prophylactic, pre-treatment regimes that prove to be therapeutically-ineffective in long-established, often progressive, MS. FTY720 (fingolimod/Gilenya) is a sphingosine-1-phosphate receptor modulator. This is a new oral agent that markedly reduces the number of relapses in people with MS, compared with currently licensed injectable agents such as the beta interferons. FTY720 has activity against lymphocytes but may also influence oligodendroglia and could therefore have the potential to influence progressive MS, by promoting remyelination.

METHODS

The effect of FTY720 was assessed in relapsing-progressive EAE in mice.

RESULTS

Early intervention during relapsing EAE could completely inhibit subsequent relapses, inhibited the accumulation of neurodegeneration, and facilitated motor recovery. However, when examined in secondary progressive EAE, that develops after the accumulation of deficit from relapsing disease, long-term treatment with FTY720 failed to slow deterioration when initiated late (4 months) into the disease course.

CONCLUSIONS

This study indicates that early intervention with immunosuppressive agents may inhibit the generation of the neurodegenerative microenvironment, which is no longer responsive to potent immunosuppression. However, if treatment is initiated too late, progressive, neurological-disease continues unabated. This suggests that immunosuppression is insufficient to control secondary progression in animals, as has been found so far to be the case in MS, and may warrant early intervention with FTY720 for optimal treatment benefit.

Critical appraisal of animal models of multiple sclerosis

Experimental autoimmune encephalomyelitis (EAE) is a spectrum of neurological disorders in laboratory animals that is used to model multiple sclerosis (MS). However, few agents have translated from efficacy in EAE to the treatment of human disease. Although this may reflect species differences in pathological disease mechanisms, importantly it may also relate to the practice of how drugs and models are currently used. This often bears very little resemblance to the clinical scenarios where treatments are investigated, such that lack of appreciation of the biology of disease may doom drugs to failure. The use of EAE is critically appraised with the aim of provoking thought, improving laboratory practise and aiding researchers and reviewers to address quality issues when undertaking, reporting and interpreting animal studies related to MS research. This is important as many researchers using EAE could and should do more to improve the quality of the studies.

Active induction of experimental allergic encephalomyelitis

This protocol details a method to actively induce experimental allergic encephalomyelitis (EAE), a widely used animal model for studies of multiple sclerosis. EAE is induced by stimulating T-cell-mediated immunity to myelin antigens. Active induction of EAE is accomplished by immunization with myelin antigens emulsified in adjuvant. This protocol focuses on induction of EAE in mice; however, the same principles apply to EAE induction in other species. EAE in rodents is manifested typically as ascending flaccid paralysis with inflammation targeting the spinal cord. However, more diverse clinical signs can occur in certain strain/antigen combinations in rodents and in other species, reflecting increased inflammation in the brain.

Biozzi mice: Of mice and human neurological diseases

In 1972 Guido Biozzi selectively bred mice to study the immunopathological mechanisms underlying polygenic diseases. One line, the Biozzi antibody high (AB/H) mouse (now designated the ABH strain) was later found to be highly susceptible to many experimentally induced diseases such as autoimmune encephalomyelitis, autoimmune neuritis, autoimmune uveitis, as well as virus-induced demyelination and has thus been a key mouse strain to study human inflammatory neurological diseases. In this paper we discuss the background of the Biozzi ABH mouse and review how studies with these mice have shed light on the pathogenic mechanisms operating in chronic neurological disease.

Autoimmune tolerance eliminates relapses but fails to halt progression in a model of multiple sclerosis

To date there has been poor translation of immunotherapies from rodent models to treatment of progressive multiple sclerosis (MS). In the robust, relapsing Biozzi ABH mouse model of MS, using a combination of a transient deletion of T cells followed by intravenous (i.v.) myelin antigen administration, established relapsing disease in EAE can be effectively silenced. However, when treatment was initiated in late stage chronic-relapsing disease, despite inhibition of further relapses, mice demonstrated evidence of disease progression shown by a deterioration in mobility and development of spasticity and indicates that targeting relapsing, immunological components of MS alone is unlikely to be sufficient to control progression in the late stages of MS.

Epitope spread is not critical for the relapse and progression of MOG 8-21 induced EAE in Biozzi ABH mice

Emerging autoimmunity (epitope-spreading) generated as a consequence of myelin damage is suggested to underlie the relapses in multiple sclerosis (MS). Myelin oligodendrocyte glycoprotein (MOG 8-21) induces relapsing EAE in ABH mice characterized by broadening of the autoimmune reportoire. Despite epitope spreading tolerance to the priming antigen, but not emerging epitope reactivities, resulted in long-term inhibition of clinical relapse. In contrast, spinal cord homogenate induced EAE was dominated by a proteolipid protein (PLP 56-70) autoreactivity despite the plethora of CNS antigens in the immunogen. This data suggests that during relapsing-remitting demyelinating disease the pathogenic process is dominated by the initiating antigen, with only a minor role played by emerging T-cell populations. These findings may have important implications for the efficacy of antigen-based immune therapies in autoimmune disorders.

Molecular approaches to spinal cord repair

Axon growth inhibitors associated with myelin and the glial scar contribute to the failure of axon regeneration in the injured adult mammalian central nervous system (CNS). A number of these inhibitors, their receptors, and signaling pathways have been identified. These inhibitors can now be neutralized by a variety of approaches that point to the possibility of developing new therapeutic strategies to stimulate regeneration after spinal cord injury.

Immunization with myelin or recombinant Nogo-66/MAG in alum promotes axon regeneration and sprouting after corticospinal tract lesions in the spinal cord

We have shown previously that immunization with myelin in incomplete Freund's adjuvant (IFA) is able to promote robust regeneration of corticospinal tract fibers in adult mice. In the present study the effectiveness of such immunization with myelin was compared to that of a combination of two axon growth inhibitors in myelin, Nogo-66 (the 66-amino-acid inhibitory region of Nogo-A) and myelin-associated glycoprotein (MAG). The effectiveness of two adjuvants, IFA and aluminum hydroxide (Alum), was also compared, the latter being one that can be used in humans. In addition, larger dorsal overhemisections were made at the lower thoracic level, which resulted in a larger scar. These studies were carried out in SJL/J mice, a mouse strain that is susceptible to autoimmune experimental allergic encephalomyelitis (EAE). None of the immunized mice developed EAE. Long-distance axon regeneration and sprouting of the corticospinal tract was seen in myelin and Nogo-66/MAG immunized mice. Alum was as effective or better than IFA as the adjuvant. Overall, the robustness of axon growth and sprouting was greater in mice immunized with myelin. The abundance of this growth was less than in our earlier work in which smaller lesions were made, pointing to the possible influence of inhibitors in the scar. This work shows, however, that axon growth inhibitors in myelin can be selectively blocked using this immunization approach to promote long-distance axon regeneration in the spinal cord.

Gene therapy in autoimmune, demyelinating disease of the central nervous system

Multiple sclerosis (MS) is an immune-mediated disease of the central nervous system (CNS), where suspected autoimmune attack causes nerve demyelination and progressive neurodegeneration and should benefit from both anti-inflammatory and neuroprotective strategies. Although neuroprotection strategies are relatively unexplored in MS, systemic delivery of anti-inflammatory agents to people with MS has so far been relatively disappointing. This is most probably because of the limited capacity of these molecules to enter the target tissue, because of exclusion by the blood-brain barrier. The complex natural history of MS also means that any therapeutic agents will have to be administered long-term. Gene therapy offers the possibility of site-directed, long-term expression, and is currently being preclinically investigated in experimental autoimmune encephalomyelitis (EAE), an animal model of MS. While some immune effects may be targeted in the periphery using DNA vaccination, strategies both viral and nonviral are being developed to target agents into the CNS either via direct delivery or using the trafficking properties of cell-carrier systems. Targeting of leucocyte activation, cytokines and nerve growth factors have shown some promising benefit in animal EAE systems, the challenge will be their application in clinical use.

IL-1 receptor-associated kinase 1 regulates susceptibility to organ-specific autoimmunity

Infections often precede the development of autoimmunity. Correlation between infection with a specific pathogen and a particular autoimmune disease ranges from moderately strong to quite weak. This lack of correspondence suggests that autoimmunity may result from microbial activation of a generic, as opposed to pathogen-specific host-defense response. The Toll-like receptors, essential to host recognition of microbial invasion, signal through a common, highly conserved pathway, activate innate immunity, and control adaptive immune responses. To determine the influence of Toll/IL-1 signaling on the development of autoimmunity, the responses of wild-type (WT) mice and IL-1R-associated kinase 1 (IRAK1)-deficient mice to induction of experimental autoimmune encephalomyelitis were compared. C57BL/6 and B6.IRAK1-deficient mice were immunized with MOG 35-55/CFA or MOG 35-55/CpG DNA/IFA. WT animals developed severe disease, whereas IRAK1-deficient mice were resistant to experimental autoimmune encephalomyelitis, exhibiting little or no CNS inflammation. IRAK1-deficient T cells also displayed impaired Th1 development, particularly during disease induction, despite normal TCR signaling. These results suggest that IRAK1 and the Toll/IL-1 pathway play an essential role in T cell priming, and demonstrate one means through which innate immunity can control subsequent development of autoimmunity. These findings may also help explain the association between antecedent infection and the development or exacerbations of some autoimmune diseases.

Passive transfer of experimental autoimmune labyrinthitis

The aim of the present study was to establish an animal model of autoimmune labyrinthitis using heterologous inner ear antigen (IEAg) and to elucidate whether the experimentally induced labyrinthitis could be passively transferred. Cochlear and vestibular membranous labyrinthine tissues from bovine temporal bones were used as IEAg. Donor mice were inoculated intracutaneously at multiple sites with an emulsion consisting of equal parts of IEAg and complete Freund's adjuvant. After 10 days, mononuclear cells were collected from lymph nodes, spleen and blood of the donor mice and injected intravenously into naive recipient mice. Cellular infiltration was observed in the perilymphatic space of the cochlea of all donor and recipient mice. Endolymphatic hydrops was also observed in 63% of donor and 42% of recipient mice. These findings suggest that the experimentally induced labyrinthitis observed in this animal model was probably due to an autoimmune reaction to the IEAg and was passively transferred by a cell-mediated immune reaction.

CpG oligonucleotides are potent adjuvants for the activation of autoreactive encephalitogenic T cells in vivo

The mechanism of action of microbial adjuvants in promoting the differentiation of autoimmune effector cells remains to be elucidated. We demonstrate that CpG-containing oligodeoxynucleotides (ODN) can completely substitute for heat-killed mycobacteria in the priming of encephalitogenic myelin-reactive T cells in vivo. The adjuvanticity of the CpG ODN was secondary to their direct ability to induce IL-12 or to act synergistically with endogenous IL-12 to promote Th1 differentiation and encephalitogenicity. T cells primed in the absence of CpG with Ag and IFA alone appeared to be in a transitional state and had not undergone differentiation along a conventional Th pathway. Unlike Th2 cells, they expressed low levels of the IL-12R beta 2 subunit and retained the ability to differentiate into encephalitogenic effectors when reactivated in vitro under Th1-polarizing conditions. These results support the use of CpG ODN as adjuvants but also suggest that they could potentially trigger autoimmune disease in a susceptible individual.

Encephalitogenic and immunogenic potential of the stress protein alphaB-crystallin in Biozzi ABH (H-2A(g7)) mice

The stress protein alphaB-crystallin is an immunodominant antigen in multiple sclerosis (MS)-affected myelin for human T cells and is expressed at elevated levels in MS lesions. Using bovine alphaB-crystallin and synthetic peptides based on mouse alphaB-crystallin the ability of this stress protein to induce experimental allergic encephalomyelitis (EAE) was screened in Biozzi ABH (H-2A(g7)) mice. While whole alphaB-crystallin and the immunodominant T cell epitopes (49-64, 73-88, 153-168) failed to induce disease the subdominant or cryptic epitope (1-16) was weakly encephalitogenic. The lack of encephalitogenicity of whole protein and dominant epitopes may be due to the low constitutive expression of alphaB-crystallin in the CNS combined with a state of peripheral tolerance suggested by the constitutive expression of alphaB-crystallin in secondary lymphoid tissues in ABH mice. Further evidence for a role of alphaB-crystallin in the progression of chronic relapsing neurological disease is suggested by the development of T cell responses to alphaB-crystallin during MOG-induced relapsing EAE as myelin damage accumulates. Together our data indicate that normal tolerising mechanisms in ABH mice prevent the induction of EAE by alphaB-crystallin while the subdominant or cryptic epitope is able to circumvent these mechanisms and contribute to pathogenic myelin-directed autoimmunity following T cell activation.

A therapeutic vaccine approach to stimulate axon regeneration in the adult mammalian spinal cord

Axon growth inhibitors associated with myelin play an important role in the failure of axon regeneration in the adult mammalian central nervous system (CNS). Several inhibitors are present in the mature CNS. We now present a novel therapeutic vaccine approach in which the animals' own immune system is stimulated to produce polyclonal antibodies that block myelin-associated inhibitors without producing any detrimental cellular inflammatory responses. Adult mice immunized in this manner showed extensive regeneration of large numbers of axons of the corticospinal tracts after dorsal hemisection of the spinal cord. The anatomical regeneration led to recovery of certain hind limb motor functions. Furthermore, antisera from immunized mice were able to block myelin-derived inhibitors and promote neurite growth on myelin in vitro.

Optic neuritis in chronic relapsing experimental allergic encephalomyelitis in Biozzi ABH mice: demyelination and fast axonal transport changes in disease

The encephalitogenicity of optic nerve tissue was demonstrated in Biozzi ABH (H-2(dq1)) mice. Acute experimental allergic encephalomyelitis (EAE) occurred in 11/14 animals and 4/5 exhibited relapse. The involvement of the optic nerve in spinal cord homogenate induced chronic relapsing EAE (CREAE) was demonstrated by mononuclear cell infiltration and myelin degradation in the optic nerve prior to and during clinical disease. During the relapse phase gross pathological assessment revealed swollen and translucent plaques on the optic nerves. Advanced lesions showed widespread demyelination, astrocytic gliosis and fibrotic changes of the blood vessels. Physiologically, the fast axonal transport of proteins from the retina to the optic nerve and superior colliculus was significantly decreased during relapse. The association of inflammation and demyelination with physiological deficit in the optic nerve highlights the usefulness of this model in the study of multiple sclerosis in which acute monosymptomatic unilateral optic neuritis is a common manifestation. Furthermore, the novel induction of CREAE with optic nerve homogenate suggests that optic neuritis is a common significant role in the pathophysiology and progression of neurological disease in CREAE which may be relevant to studies of optic neuritis in multiple sclerosis.

Control of immune-mediated disease of the central nervous system with monoclonal (CD4-specific) antibodies

Chronic relapsing experimental allergic encephalomyelitis (CREAE) was induced in Biozzi AB/H (H-2dq1) mice by active sensitization with spinal cord antigens. A single i.p. injection of CD8-depleting (YTS169.4) monoclonal antibody (mAb) failed to affect the clinical course of CREAE when administered prior to and during the onset of both the initial clinical and subsequent relapse phase of the disease. By contrast similar treatment with both CD4-depleting (YTS191.1) or CD4-blocking/non-depleting (YTS177.9) mAb significantly inhibited disease progression. Treatment shortly before the anticipated onset of clinical EAE prevented the subsequent development of disease, although disease could be provoked following antigen-rechallenge. In contrast, treatment with these antibodies during post-acute remission phase mainly served to delay the incidence of relapse. This suggests that, unless tolerance can be re-induced, treatment of ongoing neuroimmunological disease will require 'pulse' therapy and thus potentiate the problems of long-term immunosuppresion. Despite the findings that CD4-specific antibodies can rapidly reverse overt clinical disease shortly after the onset of disease exacerbation, once neurological dysfunction becomes established anti-CD4 treatment fails to improve the animals clinically, possibly due to the inability to rapidly reverse established demyelination. Although this study does not exclude the potential central action of the injected mAb, the failure to significantly dissociate therapeutic benefit between mAb administered directly into the CNS and that given systemically suggests that a major action of these agents is probably by selectively removing T cells in the peripheral T cell pool.