Caspase-1 knockout mice have defects in SphK2 processing and release during apoptosis. Spleen cells from caspase-1 knockout (Casp1^−/−; n = 7) and wild-type (Casp1^+/+; n = 7) littermates were left untreated or incubated with Sts. (A) Dot blots show FACS analysis of spleen cell subsets after preparation from whole spleens. CD45⁺ cells were further stained with CD3-FITC, CD4-APC (T cells), CD19-APC (B cells), F4/80-APC (macrophages), and/or respective isotype antibodies. Representative data from 3 different mice of each genotype are displayed. (B) FACS dot blots display PS exposure visualized with annexin V–FITC in spleen cell conglomerates before and after incubation with Sts for 2 and 4 hours. CD4-APC staining specifies apoptosis mainly in the T-cell compartment. Representative data from 5 different mice of each genotype are displayed. (C) Western analysis of cytosolic SphK2 expression before and after induction of apoptosis with Sts. The histogram shows quantification of Western data as means ± SEM from 5 mice of each genotype. (D) Histogram shows SphK2 activity in the supernatants of control or Sts-treated spleen cell conglomerates. Data are means ± SEM from 7 different mice of each genotype. ***P < .001.