CD93+ Early Stage B Cells Interact With Dll-1 Expressing Cells in Mouse Spleen

Abstract

The region at the interface of the red pulp and the white pulp of the spleen and which separates them is called the marginal zone. The main type of cells in the marginal zone are marginal zone B (MZ B) cells as well as two unique macrophage populations. In mice, MZ B cells are a unique population of B cells, distinct from follicular(FO) B cells. MZ B cells have a IgMhiIgDloCD23-CD21hiCD1dhi surface phenotype. Because of the high expression of CD21, MZ B cells can bind to immune complexes containing circulating antigens and blood-borne pathogens. Two key factors appear to influence immature B cells to develop into MZ B cells- the specificity and strength of the BCR and Notch signaling through Notch2. Notch signaling may be required for the differentiation of B cells into MZ B cells or for the maintenance of MZ B cells. The Notch family genes play a key role in cellular differentiation in many organisms. Previous studies showed the importance of the conserved cell-to-cell signaling cascade of Notch signaling in lymphocyte development. Notch2 is indispensable for MZ B cell development and must be ligated by the Dll-1Notch ligand. Expression of Notch ligands on different cells in the spleen has been reported. Interactions between Dll-1 expressing cells and B cells have not been previously demonstrated or described. Our results in this thesis demonstrate cell-cell contact between Dll-1 expressing cells and CD93+early stage B cells, and it is suggested the CD93+ cells are T2 cells by the expression level of Notch2 from IMMGen database. These data suggest that Dll-1 must ligate Notch-2 at an early transitional stage of peripheral B cell development for MZ B cell development to occur.