Figure 5.

BCR^low GC B Cells Undergo Apoptosis during Late G1 in the DZ

Fucci2 mice were immunized with SRBCs and splenic IgD^low CD95⁺ GL7⁺ GC B cells were analyzed on day 10. (A and B) GC B cells were stained with LZ/DZ markers and with anti- act-Casp3.

(C) The timing of cell cycle re-entry from the DZ or surface CXCR4 decreases by G1 GC B cells was determined by examining mCherry levels. Yellow area indicates a likely fate junction where cells must be committed one of these processes.

(D and E) DZ, act-Casp3⁺ DZ, and BCR^low act-Casp3⁺ DZ cells were gated and levels of the cell cycle regulated Fucci2 florescent reporters were examined. Cell-cycle stages are gated in (D) and mean frequencies ± SD are shown, with summaries in (E).

(F) BCR (Igβ) levels on total GC B cells and act-Casp3⁺ GC B cells.

(G) Frequency of BCR^high and BCR^low DZ cells that were act-Casp3⁺.

(H) mCherry levels in LZ, DZ, and Act-Casp3⁺ cells are shown. Plots and graphs in (A–C) are representative of 13 mice from 4 experiments; plots and means (+/− SD) in (D–H) are compiled from, or representative of (F and H), of 9 mice from 3 experiments. Each point in (B, E, G) represents a single mouse. Analysis was performed using an unpaired two-tailed Student’s t test. ^∗∗∗p < 0.001. See also Figure S4.