Effect of Brd4 deficiency on efficient plasma cell differentiation in mice with B cell-specific deletion of the Brd4 gene
To further evaluate the in vivo function of Brd4 in modulating plasma cell differentiation, Brd4-CKO mice were generated by using the Cre-LoxP system (Fig. 3 A and B). Brd4 flox mice (Brd4f/f, designated hereafter as “FL/FL” mice) were bred with CD19-Cre mice to generate B cell-specific deletion of Brd4 mice (Brd4f/f, CD19cre/-, hereafter designated as “CKO” mice). Mice carrying Brd4f/f and CD19-Cre (Brd4f/f, CD19cre/-) were born at the expected Mendelian ratio and developed normally when housed in a pathogen-free facility. RT-qPCR confirmed the tissue-specific deletion of Brd4 in B cells (Fig. 3C).
To determine the requirement of Brd4 for terminal B cell differentiation into plasma cells, the ability of Brd4 deficient B cells to form plasma cells in vitro was assessed. B cells isolated from the spleen, lymph nodes and PBMCs were induced to differentiate using lipopolysaccharide (LPS, 10 μg/mL) and IL-4 (10 ng/mL). We observed a reduced percentage of CD138+ plasma cells but not naïve B cells (CD19+IgD+CD27-) or memory B cells (CD19+IgD-CD27+) in Brd4-CKO mice compared with FL/FL (Fig. 3D, E, F,G). These findings provide more solid evidence for a critical role of Brd4 in regulating plasma cell differentiation.