Analysis of the organization and signaling capacity of the membrane IgE during its interaction with CD19 and CD23 in B lymphocytes
by Christina Gabriela Kerntke
Date of Examination:2021-07-21
Date of issue:2021-07-27
Advisor:Prof. Dr. Jürgen Wienands
Referee:Prof. Dr. Jürgen Wienands
Referee:Prof. Dr. Michael Thumm
Files in this item
This file will be freely accessible after 19.07.2022.
EnglishThe predominant allergy type I (hypersensitivity reaction type I) poses an increasing health issue in industrialized countries over the last decades. A key mediator in the pathogenesis of hypersensitivity or allergic diseases is IgE and its interaction with the IgE-specific FcεRI. This makes IgE a promising target for the treatment of allergic disorders. Currently, immunotherapies of patients with severe allergies are based on neutralizing soluble IgE, which inhibits the IgE FcεRI association. This strategy, however, does not target IgE that is already bound, which is why the therapy has to be performed on a regular basis. Therefore, studies about IgE synthesis and its regulation are of great importance. In vivo studies of the biology of IgE, however, are difficult not only because of the scarcity of IgE+ B cells but also due to the difficulty to identify IgE+ B cells, since serum IgE also binds to FcεRs expressed on all B cells. The development of transgenic mouse models in the last decade, though, enabled the identification of mIgE expressing B cells and their further functional analysis. By analyzing murine and human mIgE BCRs in B cell lines, this thesis focused on its interaction with the B cell co-receptor CD19 and the IgE-specific receptor CD23. Previous studies, using murine in vitro B cell models, proposed that the murine mIgE-BCR appears to regulate the terminal differentiation of IgE-switched B cells into plasma cells in an autonomous way. In particular, CD19 appeared to play an essential role in this context, which implied a direct interaction with the murine mIgE-BCR. The first task of this thesis was to test this interaction. Despite the application of exactly the same affinity-purification approach, which was the base for the reported mIgE-CD19 interaction, such receptor interaction could not be revealed. The same could be observed through a more specified approach. The data presented herein hint to unspecific interactions between the used affinity-matrix and CD19, which might have falsified the reported interaction. Alternatively, the interaction between murine mIgE and CD19 may require additional, unknown intermediates not expressed in my cellular model system. Studies about the regulation of IgE are essential especially in regard to the potentially life threatening impact of IgE in anaphylactic reactions. A crucial factor in the regulation of IgE expression is CD23, as studies on transgenic mouse models lacking or overexpressing CD23 have shown. This study reveals an association between the human mIgE-BCR isoforms and CD23, which appears to significantly inhibit the surface expression of the mIgE isoform, mIgE-S. In particular, basis for the inefficient surface expression of mIgE-S appears to be an impaired assembly of the Igα/Igβ heterodimer with mIgE as a result from the mIgE-CD23 assocation. The reduced surface expression of mIgE-BCR was accompanied by significantly hampered Ca2+ signaling, observed in co-expression of CD23. Similar observations could be made in a human B cell model, expressing IgE in more physiological amounts by using its endogenous IgE heavy chain promotor.
Keywords: mIgE-BCR; CD23; Hypersensitivity; B lymphocyte; CD19