Multiple sclerosis (MS) is widely considered to be the result of an aggressive autoreactive T cell attack on myelin. How these autoimmune responses arise in MS is unclear, but they could result from virus infections. Thus, viral and autoimmune diseases in animals have been used to investigate the possible pathogenic mechanisms operating in MS. The autoimmune model, experimental autoimmune encephalomyelitis, is the most widely-used animal model and has greatly influenced therapeutic approaches targeting autoimmune responses. To investigate demyelination and remyelination in the absence of the adaptive immune response, toxin-induced demyelination models are used. These include using cuprizone, ethidium bromide and lysolecithin to induce myelin damage, which rapidly lead to remyelination when the toxins are withdrawn. The virus models include natural and experimental infections such as canine distemper, visna infection of sheep, and infection of non-human primates. The most commonly used viral models in rodents are Semliki Forest virus and Theiler's murine encephalomyelitis virus. The viral and experimental autoimmune encephalomyelitis models have been instrumental in the understanding of how viruses trigger inflammation, demyelination and neurodegeneration in the central nervous system. However, due to complexity of the animal models, pathological mechanisms are also examined in central nervous system cell culture systems including co-cultures, aggregate cultures and brain slice cultures. Here we critically review in vitro and in vivo models used to investigate MS. Since knowledge gained from these models forms the basis for the development of new therapeutic approaches for MS, we address the applicability of the models. Finally, we provide guidance for using and reporting animal studies with the aim of improving translational studies to the clinic.

Neuroaxonal degeneration is a pathological hallmark of multiple sclerosis (MS) contributing to irreversible neurological disability. Pathological mechanisms leading to axonal damage include autoimmunity to neuronal antigens. In actively demyelinating lesions, myelin is phagocytosed by microglia and blood-borne macrophages, whereas the fate of degenerating or damaged axons is unclear. Phagocytosis is essential for clearing neuronal debris to allow repair and regeneration. However, phagocytosis may lead to antigen presentation and autoimmunity, as has been described for neuroaxonal antigens. Despite this notion, it is unknown whether phagocytosis of neuronal antigens occurs in MS. Here, we show using novel, well-characterized antibodies to axonal antigens, that axonal damage is associated with HLA-DR expressing microglia/macrophages engulfing axonal bulbs, indicative of axonal damage. Neuronal proteins were frequently observed inside HLA-DR 1 cells in areas of axonal damage. In vitro, phagocytosis of neurofilament light (NF-L), present in white and gray matter, was observed in human microglia. The number of NF-L or myelin basic protein (MBP) positive cells was quantified using the mouse macrophage cell line J774.2. Intracellular colocalization of NF-L with the lysosomal membrane protein LAMP1 was observed using confocal microscopy confirming that NF-L is taken up and degraded by the cell. In vivo, NF-L and MBP was observed in cerebrospinal fluid cells from patients with MS, suggesting neuronal debris is drained by this route after axonal damage. In summary, neuroaxonal debris is engulfed, phagocytosed, and degraded by HLA-DR 1 cells. Although uptake is essential for clearing neuronal debris, phagocytic cells could also play a role in augmenting autoimmunity to neuronal antigens. V

Immunoreactivity to plasma NF-L and homologous NF proteins is informative of the stage of disease progression in ALS. The determination of NF antibody levels in plasma could be added to the growing panel of disease-monitoring biomarkers in ALS targeting cytoskeletal antigens.

Drug efficacy in MS treatment indicates the potential use of monitoring the content of antibodies against the NF-L chain as a predictive biomarker of treatment response in MS.

BackgroundAutoimmunity to neuronal proteins occurs in several neurological syndromes, where cellular and humoral responses are directed to surface as well as intracellular antigens. Similar to myelin autoimmunity, pathogenic immune response to neuroaxonal components such as neurofilaments may contribute to neurodegeneration in multiple sclerosis.MethodsWe studied the immune response to the axonal protein neurofilament light (NF-L) in the experimental autoimmune encephalomyelitis animal model of multiple sclerosis. To examine the association between T cells and axonal damage, pathology studies were performed on NF-L immunized mice. The interaction of T cells and axons was analyzed by confocal microscopy of central nervous system tissues and T-cell and antibody responses to immunodominant epitopes identified in ABH (H2-Ag7) and SJL/J (H2-As) mice. These epitopes, algorithm-predicted peptides and encephalitogenic motifs within NF-L were screened for encephalitogenicity.ResultsConfocal microscopy revealed both CD4+ and CD8+ T cells alongside damaged axons in the lesions of NF-L immunized mice. CD4+ T cells dominated the areas of axonal injury in the dorsal column of spastic mice in which the expression of granzyme B and perforin was detected. Identified NF-L epitopes induced mild neurological signs similar to the observed with the NF-L protein, yet distinct from those characteristic of neurological disease induced with myelin oligodendrocyte glycoprotein.ConclusionsOur data suggest that CD4+ T cells are associated with spasticity, axonal damage and neurodegeneration in NF-L immunized mice. In addition, defined T-cell epitopes in the NF-L protein might be involved in the pathogenesis of the disease.

Antibodies to neuronal antigens are associated with many neurological diseases including paraneoplastic neurological disorders, epilepsy, amyotrophic lateral sclerosis and multiple sclerosis. Immunization with neuronal antigens such as neurofilament light (NF-L), a neuronal intermediate filament in axons, has been shown to induce neurological disease and spasticity in mice. Also, although antibodies to NF-L are widely used as surrogate biomarkers of axonal injury in amyotrophic lateral sclerosis and multiple sclerosis, it remains to be elucidated if antibodies to NF-L contribute to neurodegeneration and neurological disease. To address this, we examined the pathogenic role of antibodies directed to NF-L in vitro using spinal cord co-cultures and in vivo in experimental autoimmune encephalomyelitis (EAE) and optic neuritis animal models of multiple sclerosis. Here we show that peripheral injections of antibodies to NF-L augmented clinical signs of neurological disease in acute EAE, increased retinal ganglion cell loss in experimental optic neuritis and induced neurological signs following intracerebral injection into control mice. The pathogenicity of antibodies to NF-L was also observed in spinal cord co-cultures where axonal loss was induced. Taken together, our results reveal that as well as acting as reliable biomarkers of neuronal damage, antibodies to NF-L exacerbate neurological disease, suggesting that antibodies to NF-L generated during disease may also be pathogenic and play a role in the progression of neurodegeneration.

An increased prevalence of the inflammatory bowel diseases, ulcerative colitis and Crohn’s disease, was found amongst residents in a livestock dense area. We hypothesised that exposure to livestock farms might be a substantial environmental factor that contributes to the development of these diseases and that in the lead up to inflammatory bowel diseases potential risk factors can be identified. This study aimed to investigate the contribution of livestock exposure to the development of these diseases and the clinical events prior to the diagnosis. Electronic health records from 2006–2013 of general practices were used. The study population consisted of patients with a new diagnosis of inflammatory bowel diseases resident in areas with a high (n = 141) or lower (n = 109) livestock density. Patients with low back pain (n = 10,469) were used as controls. For those in a livestock dense area, distance to livestock farms was determined. Associations between morbidities and drug prescriptions in the reporting year and three years previous to the diagnosis, and the residential proximity to livestock exposure were investigated with multivariable logistic regression analyses. Acute and chronic morbidity of the gastrointestinal tract and associated drug prescriptions were predictive for the development of inflammatory bowel diseases. In addition, a positive association was found between infections and living within 500 meter of poultry farms and the development of inflammatory bowel diseases [OR: 3.3 (1.1–9.9)]. Nonetheless, overall livestock exposure contributed little to the development of these diseases. These results suggest that exposure to livestock farms on its own contributes minimal to the development of inflammatory bowel diseases. Nonetheless, having infections appeared to be a risk factor for neighbouring residents of poultry farms. More research is warranted to explain the increased prevalence of inflammatory bowel diseases amongst residents in areas with a high density of livestock.