Identifying targets for autoantibodies in CNS inflammation: Strategies and achievements

Group A streptococcal antigen exposed rat model to investigate neurobehavioral and cardiac complications associated with post-streptococcal autoimmune sequelae

Background

The neuropsychiatric disorders due to post-streptococcal autoimmune complications such as Sydenham's chorea (SC) are associated with acute rheumatic fever and rheumatic heart disease (ARF/RHD). An animal model that exhibits characteristics of both cardiac and neurobehavioral defects in ARF/RHD would be an important adjunct for future studies. Since age, gender, strain differences, and genotypes impact on the development of autoimmunity, we investigated the behavior of male and female Wistar and Lewis rat strains in two age cohorts (<6 weeks and >12 weeks) under normal husbandry conditions and following exposure to group A streptococcus (GAS).

Methods

Standard behavioral assessments were performed to determine the impairments in fine motor control (food manipulation test), gait and balance (beam walking test), and obsessive-compulsive behavior (grooming and marble burying tests). Furthermore, electrocardiography, histology, and behavioral assessments were performed on male and female Lewis rats injected with GAS antigens.

Results

For control Lewis rats there were no significant age and gender dependent differences in marble burying, food manipulation, beam walking and grooming behaviors. In contrast significant age-dependent differences were observed in Wistar rats in all the behavioral tests except for food manipulation. Therefore, Lewis rats were selected for further experiments to determine the effect of GAS. After exposure to GAS, Lewis rats demonstrated neurobehavioral abnormalities and cardiac pathology akin to SC and ARF/RHD, respectively.

Conclusion

We have characterised a new model that provides longitudinal stability of age-dependent behavior, to simultaneously investigate both neurobehavioral and cardiac abnormalities associated with post-streptococcal complications.

[Diagnostic value of antibodies to myelin oligodendrocyte glycoprotein in demyelinating diseases of the central nervous system]

AIM

To evaluate the diagnostic value of MOG-IgG antibodies in multiple sclerosis (MS) and acute disseminated encephalomyelitis (ADEM).

MATERIAL AND METHODS

Twenty-nine patients with definitive MS according to the criteria of McDonald, 2010 (21 with relapse-remitting MS and 8 with secondary progressive MS), 7 patients with ADEM confirmed by clinical and instrumental data and 27 healthy volunteers were included in the study. Serum MOG-IgG levels were evaluated in all patients. MOG-IgG levels in the cerebrospinal fluid (CSF) were evaluated in 22 cases with MS, 6 cases with ADEM, and 8 healthy volunteers using ELISA.

RESULTS AND CONCLUSIONS

Serum MOG-IgG levels are significantly higher in patients with MS and ADEM compared to the control group. No statistically significant differences in the serum MOG-IgG levels were found between MS and ADEM groups. When analyzing the level of MOG-IgG in CSF, no statistically significant between-group differences were obtained. The sensitivity and specificity of the determination of MOG-IgG in serum in patients with MS are 75,8% and 92.59%, respectively. MOG-IgG is detected in serum and CSF in patients with demyelinating diseases that indicates its pathogenetic significance in the development of MS and ADEM. Serum MOG-IgG may be a valuable biomarker for demyelinating diseases. Further research in a large population of patients is required.

Untapped targets in multiple sclerosis

Multiple sclerosis is a chronic inflammatory disease of the white and grey matter which results in irrevocable axonal and neuronal damage. Grey matter injury is widespread and reflects disability to a greater extent than do white matter lesions. Growing understanding of the immunopathology of multiple sclerosis is leading the way to the identification and testing of untapped targets that may offer new and more specific ways to treat the disease. For example, data from animal models support a two-step pathological process in multiple sclerosis, whereby T cells initially induce inflammation and open up the blood-brain barrier, which then allows access to antibodies which aggravate tissue damage. Determination of the specificity of the invading T cells and the autoantibodies that cause disease is a major focus of current research. The discovery of anti-aquaporin-4 autoantibodies in patients with neuromyelitis optica and of anti-MOG antibodies in a subset of children with paediatric autoimmune demyelinating disease are promising steps in this direction. Recently, the axoglial antigens neurofascin and contactin-2/TAG-1, which are localised around the node of Ranvier, were identified as targets of an autoimmune response in multiple sclerosis. Such an autoimmune response might induce axonal injury and direct the immunopathological response to the grey matter. It is to be hoped that the outcome of such investigations will lead to the identification of patient subgroups based on their autoreactivity and new ways to treat them safely and effectively.

Glycoproteins as targets of autoantibodies in CNS inflammation: MOG and more

B cells and antibodies constitute an important element in different inflammatory diseases of the central nervous system (CNS). Autoantibodies can serve as a biomarker to identify disease subgroups and may in addition contribute to the pathogenic process. One candidate autoantigen for multiple sclerosis (MS) is myelin oligodendrocyte glycoprotein (MOG). MOG is localized at the outermost surface of myelin in the CNS and has been the focus of extensive research for more than 30 years. Its role as an important autoantigen for T cells and as a target of demyelinating autoantibodies has been established in several variants of experimental autoimmune encephalomyelitis (EAE), an animal model of MS. The literature regarding antibodies to MOG in MS patients is confusing and contradictory. Recent studies, however, have described high levels of antibodies to conformationally correct MOG in pediatric acquired demyelination, both acute disseminated encephalomyelitis (ADEM) and MS. In adult MS, such antibodies are rarely found and then only at low levels. In this review, we summarize key findings from animal models and patient studies, discuss challenges in detecting anti-MOG antibodies in patients and present recent approaches to identifying new autoantigens in MS.

Identifying autoantigens in demyelinating diseases: valuable clues to diagnosis and treatment?

PURPOSE OF REVIEW

Identification of autoantigens in demyelinating diseases is essential for the understanding of the pathogenesis. Immune responses against these antigens could be used as biomarkers for diagnosis, prognosis and treatment responses. Knowledge of antigen-specific immune responses in individual patients is also a prerequisite for antigen-based therapies.

RECENT FINDINGS

A proportion of patients with demyelinating disease have antibodies to aquaporin 4 (AQP4) or myelin oligodendrocyte glycoprotein (MOG). Patients with anti-AQP4 have the distinct clinical presentation of neuromyelitis optica (NMO), and these patients often also harbour other autoimmune responses. In contrast, anti-MOG is seen in patients with different disease entities such as childhood multiple sclerosis (MS), acute demyelinating encephalomyelitis (ADEM), anti-AQP4 negative NMO, and optic neuritis, but hardly in adult MS. A number of new candidate autoantigens have been identified and await validation. Antigen-based therapies are mainly aimed at tolerizing T-cell responses against myelin basic protein (MBP) and have shown only modest or no clinical benefit so far.

SUMMARY

Currently, only few patients with demyelinating diseases can be characterized based on their autoantibody profile. The most prominent antigens in this respect are MOG and AQP4. Further research has to focus on the validation of newly discovered antigens as biomarkers.

Humoral autoimmunity in multiple sclerosis

The important role of B cells and autoantibodies in the pathogenesis of MS is increasingly appreciated. The recruitment and maintenance of B cells and plasma cells in MS lesions is presumably based on local production of lymphoid chemokines and B cell activation factor of the TNF family (BAFF). The failure of the clinical trial with Atacicept targeting BAFF and its relative APRIL was a great surprise and cannot readily be explained. A role for BAFF in CNS physiology, e.g. via targeting of the Nogo-66 receptor might have to be considered. The identification of patient subgroups based on autoantibodies is a future challenge. Currently patients with neuromyelitis optica (NMO) can be identified by antibodies to aquaporin 4 and about a third of children with acquired demyelinating diseases have antibodies against conformationally correct MOG, while such antibodies are hardly found in adult MS patients. Searching for new targets of the autoimmune response in adult MS patients, we have identified two axo-glial proteins focused around the node of Ranvier, namely neurofascin and contactin-2/TAG-1. Testing the functional relevance of such an autoimmune response in animal models revealed that antibodies to neurofascin may induce axonal injury and that T cells specific for contactin-2/TAG-1 mediate preferentially gray matter injury.