Characterization of myelin-specific autoantibodies in an EAE mouse model
by Leonard Hammermann
Date of Examination:2023-09-18
Date of issue:2023-10-02
Advisor:Prof. Dr. Alexander Flügel
Referee:Prof. Dr. Alexander Flügel
Referee:Prof. Dr. Christine Stadelmann-Nessler
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EnglishAbstract Autoimmune diseases are caused by an attack of the immune system against own tissues, but the exact effector mechanisms may vary between individual diseases and are not yet fully understood. The autoimmune disease multiple sclerosis (MS) is characterized by autoimmune damage of the myelin sheets in the central nervous system (CNS). There is a general consensus that the autoimmune process is mainly driven by encephalitogenic T cells, but the role of B cells in the pathogenesis of MS has also recently been appreciated. Previous work in our department has focused on the role of myelin-specific B cells in the pathogenesis of EAE and on the cellular and molecular mechanisms underlying B cell-driven effects. It could be shown that the mechanism by which B cells accelerate and amplify EAE does not lies either in their potential to present antigens or to produce pro-inflammatory cytokines, but instead in their function as antibody-producing cells. The effector functions of antibodies depend on their isotype. The aim of this study was therefore to generate comparable myelin-specific autoantibodies by genetic modification of hybridoma cells that produce antibodies specific for the myelin oligodendrocyte glycoprotein (MOG; 8.18c5 hybridoma) and to test their effects in the EAE model. Using a CRISPR/Cas9 approach, the remaining mouse IgM, IgD, IgG3, IgG2a and IgA antibody classes could be generated, completing the already assembled set of IgG1, IgG2b and IgE antibodies with identical antigen specificity for MOG. We could observe that MOG-specific antibodies contribute to the pathogenesis of CNS inflammation in the context of EAE in two distinct pathways. All IgG antibodies – irrespective of their subclass – as well as IgM and IgA MOG-specific antibodies are involved in the exacerbation of CNS damage through demyelination and axonal degeneration. In contrast, only antibodies of all IgG subclasses accelerate the disease onset in active and transfer EAE experiments, but this was not observed for any of the other antibody isotypes. This disease acceleration no longer occurred in animals deficient for all known Fcγ-receptors (FcγRI-IV_ko mice), indicating that this effect is mediated via FcγR expressing immune cells. Surprisingly, FcγRI-IV_ko mice developed enhanced demyelinated lesions without any additional MOG-antibody treatment after immunization. This suggests a protective effect of FcγR, where they potentially inhibit the damaging impacts of endogenous autoantibodies, we detected in immunized animals. Therefore, we propose that the accelerating effect of all IgG antibodies and the demyelination observed for IgM, IgA and IgG antibodies are mediated by two distinct mechanisms. Besides different cell populations and molecular cues such as the complement system, FcγR seem to be central for both pathways but acting in an opposite direction. Acceleration of disease depends on FcγR expressed on myeloid cells, but these receptors simultaneously have a protective function to prevent endogenous autoantibody-mediated damage of the CNS.
Keywords: Antibody; Autoantibody; Isotypes; EAE; MOG; 8.18c5; FcγR; Multiple Sclerosis; IgM; IgD; IgG; IgE; IgA
Schlagwörter: Antibody; Autoantibody; Isotypes; EAE; MOG; 8.18c5; Multiple Sclerosis; FcγR; IgM; IgD; IgG; IgE; IgA