Role of antibodies in autoimmunity of the central nervous system
by César Cordero Gómez
Date of Examination:2019-10-29
Date of issue:2020-07-09
Advisor:Prof. Dr. Alexander Flügel
Referee:Prof. Dr. Jürgen Wienands
Referee:Prof. Dr. Heidi Hahn
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Format:PDFDescription:Cesar Cordero Gomez dissertation for the award of the degree "Doctor rerum naturalium"
EnglishAlthough T cells are the main players in multiple sclerosis (MS) and its animal model experimental autoimmune encephalomyelitis (EAE), the role of B cells and their soluble effector molecules (antibodies) is being progressively appreciated regarding disease development. Previous observations from our department showed that autoantigen-specific B cells contribute substantially to the pathogenesis of CNS autoimmune disease through the production of myelin-specific antibodies. These autoantibodies accumulated in CNS resident antigen presenting cells and facilitated the reactivation of invading autoreactive T cells, resulting in an earlier manifestation of clinical disease. These results showed that antibodies exert additional mechanisms involved in CNS autoimmune disease exacerbation, in contrast to previous studies that focused exclusively on the role of antibody-mediated demyelination in EAE exacerbation. It is known that antibody effector mechanisms are dependent on the antibody isotype. Therefore, the aim of this study was to modify the antibody isotype produced by myelin-specific hybridoma cell lines and to characterize the mechanisms by which antibodies of different isotypes exert their pathogenic functions in CNS autoimmunity. Using genetic engineering approaches based on the recently characterized CRISPR-Cas9 system, we could produce different isotypes from two hybridoma cell lines, which produce antibodies specific for myelin oligodendrocyte glycoprotein (MOG), while preserving their antigen specificity. We could demonstrate that antibody disease modifying effects were isotype-dependent in the active and transfer EAE model, with all investigated IgGs subclasses but no any other antibody isotypes tested being involved in disease acceleration. Furthermore, using a T-cell activation reporter (Nur 77-GFP) we found that IgG-treated animals presented higher percentages of activated CD4+ T cells in the CNS. Regarding the role of demyelination in EAE, our histological analysis indicated that exclusively antibodies of the IgG isotype had demyelinating potential, with IgG2a and IgG2b antibodies showing more demyelination compared to IgG1. Moreover, in the absence of Fcγ receptors (FcγR I-IV KO mice), the disease acceleration effect was abrogated but, interestingly, the demyelinating potential of antibodies of the IgG isotype was increased. Taken these results into consideration, we propose that the disease acceleration effect and CNS demyelination are two independent mechanisms driven by antibodies. While disease acceleration is dependent on the presence of Fc receptors, demyelination seems to be dependent on other molecular cues, such as the complement system. Antibody isotypes have different affinities regarding Fc receptor binding and complement fixation and, consequently, there is a preference towards one of these systems. However, the preferential effector mechanism triggered by these antibody isotypes can be altered depending on the presence, or absence, of the required molecular cues.
Keywords: Multiple sclerosis; experimental autoimmune encephalomyelitis; Central nervous system; B cells; antibodies; isotype; Fc-receptor; CRISPR-Cas9; autoimmunity; hybridoma technology; demyelination