Ritonavir decreases apoptosis in CD4⁺cells cultured with Fas agonist. Normal PBMC were cultured with Fas agonist, with and without ritonavir (5 nmol/L). Cells were stained with CD4-PE and FITC-annexin V and analyzed by flow cytometry. There was a significant (P < .05) decrease in annexin V binding in cells treated with ritonavir.