Identification of novel B-1 transitional progenitors by B-1 lymphocyte fate-mapping transgenic mouse model Bhlhe41dTomato-Cre

Abstract

B-1 lymphocytes exhibit specialized roles in host defense against multiple pathogens. Despite the fact that CD19+CD93+B220lo/-B cells have been identified as B-1 progenitors, the definition for B-1 progenitors remains to be elucidated as CD19+CD93+B220+B cells are capable to give rise to B-1 cells. Given that transcription factor Bhlhe41 is highly and preferentially expressed in B-1 cells and regulates B-1a cell development, we generated a transgenic mouse model,Bhlhe41dTomato-Cre, for fate mapping and functional analysis of B-1 cells.Bhlhe41dTomato-Cremice efficiently traced Bhlhe41 expression, which was mainly restricted to B-1 cells in B-cell lineage. We showed an efficient and specific Cre-mediated DNA recombination in adult B-1 cells and neonatal B-1 progenitors rather than B-2 cells by flow cytometric analysis ofBhlhe41dTomato-Cre/+Rosa26EYFPmice. Treatment ofBhlhe41dTomato-Cre/+Rosa26iDTRmice with diphtheria toxin revealed a robust efficacy of B-1 cell depletion. Interestingly, usingBhlhe41dTomato-Cremice, we demonstrated that neonatal B-1 progenitors (CD19+CD93+B220lo/-) expressed Bhlhe41 and were identical to well-defined transitional B-1a progenitors (CD19+CD93+B220lo/-CD5+), which only gave rise to peritoneal B-1a cells. Moreover, we identified a novel population of neonatal splenic CD19hidTomato+B220hiCD43loCD5loB cells, which differentiated to peritoneal B-1a and B-1b cells.Bhlhe41deficiency impaired the balance between CD19hidTomato+B220lo/-CD5hiand CD19hidTomato+B220hiCD5locells. Hence, we identified neonatal CD19hidTomato+B220hiCD43loCD5loB cells as novel transitional B-1 progenitors.Bhlhe41dTomato-Cre/+mouse can be used for fate mapping and functional studies of B-1 cells in host-immune responses.