Developmental and functional characterization of murine marginal zone B cells

Splenic marginal zone (MZ) compartment is uniquely localized to efficiently trap blood-borne pathogens and generate antibodies against these antigens. Given the contribution of this compartment towards protection against pathogens, particularly encapsulated bacteria, the goal of this thesis project was to understand the developmental requirements and functional characteristics of MZ B cells. Utilizing high and low MZ strains such as C3H and BALB/c, respectively, as model systems, the role of LTαβ and TNF was carefully examined in the maintenance, development and function of the MZ. Adult BALB/c and C3H mice were treated with LTαβ and/or TNF blocking reagents and their MZ organization examined by flow cytometric and histologic analysis. In addition, the status of MZ organization was correlated with antibody responses. Both strains displayed disrupted MZ organization following LTαβ and TNFα blockade and this defect correlated with impaired antibody responses. In particular, the presence of an intact MZ B cell population was shown to correlate with IgG3 antibody responses. These studies demonstrate an important cooperative role for LTαβ and TNF in MZ maintenance and optimal antibody responses.; A developmentally fixed role for LTαβ in MZ maturation was demonstrated by treating BALB/c and C3H neonates with a LTβ neutralizing antibody for the first 5 weeks of life. Neonatal blockade of LTαβ resulted in long-term disruption of MZ organization as evident by incomplete organization of this compartment and reduced MZ B cell content at 16 weeks following cessation of treatment. Together, these observations demonstrate an important role for neonatal LTαβ in MZ development. In addition, to identify the number of genes involved in controlling MZ development, high and low MZ strains were bred and genetic analyses performed. These experiments revealed that several independently segregating genes control MZ development with the low MZ phenotype being an incomplete dominant trait. Furthermore, reciprocal bone marrow transfer experiments between high and low strains indicated that hematopoietically derived cells regulate MZ development. Finally, the orphan chemokine receptor RDC1 was demonstrated to be preferentially expressed on MZ B cells using RT-PCR and real time PCR analysis.