Caspase-12 mediates nuclear apoptotic events during programmed plasma cell death. (A) Analysis of caspase-12 activation by staining with FITC-ATADfmk and flow cytometry. In vitro–differentiated plasma cells were analyzed at the time of purification (d0) and 2 days later. Undifferentiated (d0) I.29μ⁺ cells were analyzed before and after treatment with tunicamycin (1 μg/mL for 14 hours) and 3 days after LPS stimulation. Primary splenic plasma cells were analyzed 1 day after ex vivo isolation. Numbers indicate percentages of cells with positive staining from a representative experiment. (B) Freshly isolated in vitro–differentiated plasma cells and plasmacytic (d3) I.29μ⁺ cells were treated with the caspase-12 inhibitor zATADfmk (10μM) for 24 hours and stained with DAPI and for TUNEL-positive DNA fragmentation. Arrows and arrowheads indicate examples of nuclei with apoptotic chromatin condensation and TUNEL-positive DNA breaks, which were reduced significantly by treatment with zATADfmk (supplemental Figure 2D), in representative fields.