The positive and negative selection of B cells into the pre-immune repertoire

Thesis

The mechanisms of positive and negative selection of B cells and the ontogenetic switch between early and late tissue are not fully understood. The selection of mouse B1 B cells, immune components that secrete antibodies against self-antigens and common pathogens, and have a role in housekeeping and homeostasis, is known to be strongly influenced by self-antigen and BCR signalling in early ontogeny.

The objective of this thesis is to elucidate the role of GRB2, an adaptor protein, in the positive and negative selection of B cells. Furthermore, it examines the potential role of GRB2 in preserving the ontogenetic switch between early and late hematopoietic environments. Additionally, this work aims to explore the inherent differences from fetal liver (FL) and bone marrow (BM) to give rise to B1 B cells, employing single-cell transcriptomics for in-depth analysis.

In this project, addition to a B cell specific GRB2 knock-out mouse model (Grb2^f/fMb1Cre⁺ (KO)), several transgenic mouse models were utilised to investigates GRB2's role in positive selection process of B1 B cells.

It was found that the number of B1b B cells, marginal zone B cells (MZ), and serum IgM levels were increased in the absence of GRB2. The development of B1b B cells was not restricted to early-stage tissue in the absence of GRB2, the effect of which was B cell intrinsic. Regardless of the presence of antigen, GRB2 deficiency generated more B1b B cells and MZ B cells, while intracellular membrane bound self-antigen presentation further increased the number of B1b B cells by ten-fold. Single-cell immune profiling revealed a putative B1/MZ precursor population (CD19^hiB220^lowIgM^hiCD43^hiCD21^hiIgD^low) in the absence of GRB2 in adult BM, suggesting a shared developmental pathway. This study also suggested GRB2 was involved in a pathway that modulates IgM receptor levels in response to self-antigens, influencing the shift from positive to negative B cell selection, which might contribute to B1b B cell ontogeny.

In conclusion, our findings suggests that GRB2 is an intrinsic negative regulator of B1b B cell development and is required to restrict the generation of these cells in adult mice. The absence of GRB2 enhanced the positive selection by self-antigen while did not alter the requirement of appropriate self-antigen form.

Authors: Cui, J

• DOI: 10.5287/ora-n1mbqvznz
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: self-antigen; B cells; GRB2; positive selection; negative selection; B1 B cells; marginal zone B cells
• Subjects: Medicine; B cell development; Immunology; B cells