Disappearance of B cells from the MZ of irf4^fl/flCD20-TAM-Cre mice upon inhibition of NOTCH2 activation. irf4^fl/+CD20-TAM-Cre and irf4^fl/flCD20-TAM-Cre mice were treated with TAM (days 0–2) followed by a single dose of α-NRR2 (or IgG, day 13) and analyzed 72 h after antibody administration. Data show results from one representative mouse out of four (four independent experiments). (A) Spleen sections from irf4^fl/+CD20-TAM-Cre and irf4^fl/flCD20-TAM-Cre mice were stained with H&E or analyzed for expression of eGFP and IgM after in vivo treatment with IgG or α-NRR2 antibody. Bar, 500 µm. (B) CD21 and CD23 expression by CD19⁺ splenic B cells of irf4^fl/+CD20-TAM-Cre and irf4^fl/flCD20-TAM-Cre mice was assessed by flow cytometry after in vivo treatment with IgG or α-NRR2 antibodies. Numbers above gates indicate percentage of CD23⁺CD21^int FO and CD23⁻CD21^hi MZ B cells. Right plots show histogram of eGFP expression by splenic FO B cells of irf4^fl/+CD20-TAM-Cre (blue lines) and irf4^fl/flCD20-TAM-Cre (red lines) mice.