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%0 Thesis
%A Simons, Britta
%T The landscape and dynamics of plasma cells in the small intestine during homeostasis
%I RWTH Aachen University
%V Dissertation
%C Aachen
%M RWTH-2024-04504
%P 1 Online-Ressource : Illustrationen
%D 2024
%Z Veröffentlicht auf dem Publikationsserver der RWTH Aachen University
%Z Dissertation, RWTH Aachen University, 2024
%X The gastrointestinal tract is the largest interface to the external environment and thus is constantly exposed to exogenous antigen. Consequently, a well-balanced immune response is required to protect the host from pathogens and ensure homeostasis. Plasma cells play a key role in this balanced system. In fact, the gut comprises the largest total number of plasma cells in the body. Their main effector function is to generate and secrete antibodies that bind to their antigens such as food or microbiota. Antibodies, especially immunoglobulin A, contribute to host protection and maintain homeostasis with the microbiota. Currently, there is limited knowledge about the factors and mechanisms that influence the generation, development and the phenotype of plasma cells. The precise mechanism for regulating and maintaining the B cell receptor (BCR) repertoire of intestinal plasma cells is still unknown. Therefore, we tracked dynamics of antibody responses in the gut during aging in the face of different microbial colonisation and connecting different immune compartments such as the gut associated lymphoid tissue and the small intestine.To investigate whether plasma cells are a phenotypically heterogeneous population, we developed a multi-dimensional integrated approach to analyse the phenotype of plasma cells under various conditions. This integrated approach enables the detection of subtle differences that may be missed in classical non-integrated analyses. Despite major differences in the intestinal environment, we observed that plasma cells were remarkably homogenous in their phenotype. However, a gradual expression of the surface markers Ly6c and MHCII was detected. While Ly6c expression may be associated with antibody secretion, MHCII expression is associated with the maturation state of B cells. Data obtained from single cell sequencing supported this observation. MHCII expressing cells showed a proliferating phenotype indicating them to be plasma blasts. This observation was independent of age, microbiota composition and location. In addition, single cell sequencing also provided combined information on a plasma cell’s phenotype and its BCR. Plasma cells expressing the same BCR were evenly distributed across the unifold manifold approximation and projection (UMAP) and did not exhibit any specific clonal phenotype. This indicates that even clonally related cells acquire the full range of phenotypic states.The BCR repertoire of different aged mice was analysed to gain a better understanding of the dynamics of the plasma cell repertoire. We labelled active B cells in a cell fate tracking system and followed these cells for different time spans. In addition, we obtained gut biopsies to describe the composition and structure of the gut plasma cell repertoire. By comparing the clones in the biopsy and the follow-up samples, we were able to track dynamic changes in the BCR repertoire. Therefore, we speculate that young mice may generate a less diverse repertoire and more polyreactive clones, while the repertoire of adult mice may mature towards cross-species reactive or specific antigens. Moreover, young and adult mice were able to generate long-lived winner clones. These clones persisted for at least six months not only in the plasma cell pool, but also in the memory B and germinal center B cell compartment. This suggests the recruitment of memory B cells into germinal centers and a continuous maturation of these clones. However, the fraction of long-lived clones was low, indicating that the small intestinal plasma cell pool is maintained by long-lived clones but also by newly recruited clones. Additionally, we have developed an approach to analyse clonal maturation and selection by grouping clones into clonal trees.In conclusion, the analysis of the BCR repertoire in combination with cell tracking is a powerful tool for understanding the dynamics of gut B cell responses. Specific plasma cell clones can be generated and their binding and coating characteristics can subsequently be investigated, allow-ing for a deeper insight into the maturation and selection processes of plasma cells. Our results may be relevant in context of mucosal vaccination and faecal microbiota transplants. As plasma cells displayed a remarkably homogenous population, we speculate that routes of antigen encounter and underlying inductive pathways do not primarily impact plasma cell function. Nevertheless, the clonal composition seems to slowly adapt to changes in the gut environment during homeostasis. Such system might buffer short-term daily changes in the antigen pool and contribute to resilience of the microbiota. Yet eventually, continuous gut B cell responses will diversify the repertoire of gut plasma cells to provide balanced humoral responses to intestinal antigens.
%F PUB:(DE-HGF)11
%9 Dissertation / PhD Thesis
%R 10.18154/RWTH-2024-04504
%U https://publications.rwth-aachen.de/record/985174