Cell-Cell Interactions and Cell Fate Determination: Involvement of Dlk in B Cell Developmentand Function

Abstract

RATIONALE: Dlk (Delta like-1) is expressed on a subset of stroma and regulates HSC proliferation. We created a dlk -/- mouse model to investigate the importance of the stromal microenvironment for proper development and function of B cells. METHODS: FACS analysis of B cell subsets; immuno-histochemical analysis of spleen sections; in vitro differentiation of bone marrow B cells; ELISA on serum Ig before and after DNP-KLH challenge. RESULTS: Compared to wild type controls, bone marrow B cells from dlk -/- mice had a 30% increase in fraction-A cells (4-week-old mice, n=4,P<0.01), and a 2.4-fold decrease in Fraction-C cells. (P< 0.0001, 6-week old mice, n=4). In vitro differentiation of total bone marrow cells supplemented with IL7 resulted in increased (4-fold) differentiation of fraction C. Mature recirculating B cell numbers decreased 2-3 fold. Spleens of 6-week-old mice had two-fold increases in Tr1 cells. Eight-week-old mice had increased marginal zone B cells and decreased follicular B cells (P < 0.001, n=3). Serum IgG was high and upon immunization it increased dramatically for DNP specific responses (n=4 P<0.01). CONCLUSIONS: The alterations in the stroma dependent progenitor B cells, the splenic B cell subsets and the hyper IgG response indicate dlk is important in development and function of normal B cell. These results suggest that dlk could be a useful target for modulating innate humoral immune responses.