Investigations into the formation and re-activation of memory B cells

Abstract

Memory B cells are an essential part of adaptive immunity and underlie the efficacy of most vaccines. This thesis aims to examine both the formation and re-activation of memory B cells.This thesis examines the formation of memory B cells through studying combined immunodeficiency patients with mutations in the kinase STK4 with a decreased number of memory B cells in peripheral blood. A novel Stk4Y88del/Y88del mutation was identified in two patients and a mouse model with the same Stk4Y88del/Y88del mutation was generated by CRISPR/Cas9 gene editing. This mouse model was utilised to show that this mutation is pathogenic and results in a B cell-intrinsic defect in B cell development with decreased number of follicular B cells, marginal zone B cells and B-1a cells. STK4 was also found to play a key role in the T cell-dependent B cell immune responses, and is required for the normal expansion and composition of the germinal centre, the formation of memory B cells and the secretion of antigen-specific antibodies.In addition to the generation of memory B cells, this thesis examines the reactivation of memory B cells in the lymph node. Utilising intravital two-photon microscopy, memory B cells were found to preferentially localise in the subcapsular region of draining lymph nodes, where they reside with an increased residence time compared to naive B cells. Upon re-activation, memory B cells were reactivated in a unique structure, the subcapsular proliferative foci, which is functionally, phenotypically and spatially distinct from the germinal centre. Memory B cells underwent efficient intrafollicular expansion and differentiation into antibody-secreting cells in the subcapsular proliferative foci, an area where antigen and T cell help is concentrated. This provides a previously unappreciated mechanism for the rapid kinetics of the secondary antibody response. Importantly, it is this rapid secretion of antibodies that protects the host from re-infection, well before long lived plasma cells derived from secondary GCs are generated. The SPF was also found to be evolutionarily conserved suggesting this may be an important consideration for generation of a robust vaccine induced memory B cell and antibody secreting cell response