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.