Ritonavir decreases ICE expression in CD4⁺cells cultured with Fas agonist. Normal PBMC were cultured with and without ritonavir. Cells were surface-stained with CD4-PE, permeabilized, and stained with ICE-FITC. CD4⁺ cells expressing ICE are shown. There was a significant, dose-dependent decrease in ICE expression (P < .01).