Figure 5: CTL function in patients with malignant mesothelioma and individuals positive for pleural plaque. Both 16 plaque-positive individuals and 14 mesothelioma patients showed a high percentage of perforin+ cells in CD8+ lymphocytes, compared with 16 healthy volunteers, whereas a decrease after stimulation was observed in mesothelioma. These findings indicate that CD8+ lymphocytes are stimulated by some kind of “nonself” cells in both plaque-positive individuals and mesothelioma patients, and that poststimulation maintenance of cytotoxicity is impaired in mesothelioma.