Proteinase inhibitor 9 (PI-9) and bcl-2 expression in lymphoma cells. Proteinase inhibitor 9 (PI-9) expression (A) and bcl-2 expression (B) were determined by flow cytometry. HLA-A2–positive lymphoma cells (▪) were used later for CTL experiments. HLA-A2–negative cells are indicated with □. Background fluorescence intensity was subtracted. Means and standard error of the mean (SEM) of 3 experiments are shown for cell lines (Ai and Bi). One out of 2 experiments is shown for primary lymphoma cells (Aii and Bii). Concordant results were obtained in both experiments. MFI indicates mean fluorescent intensity.