Macrophages from cancer patients: Analysis of TRAIL, TRAIL receptors, and colon tumor cell apoptosis

Background: Tumor-infiltrating macrophages secrete cytokines, including Fas ligand, tumor necrosis factor-alpha (TNF-alpha), and TNF-related apoptosis-inducing ligand (TRAIL). TRAIL induces apoptosis in tumor cells but not in normal cells; however, regulation of TRAIL and its receptors in cancer patients is relatively uncharacterized. We investigated whether macrophages from cancer patients produce TRAIL and whether apoptosis in cultured colon adenocarcinoma cells involves TRAIL and its receptors. Methods: Macrophages isolated from pleural effusions of nine cancer patients and five control patients with congestive heart failure (whose effusions contained no tumor cells) were cultured. Levels of TRAIL, TNF-alpha, interferon alpha, and Fas ligand in conditioned medium were measured by enzyme-linked immunosorbent assays. Apoptosis of human colon adenocarcinoma cell lines, including Colo 205, was determined by the Annexin V method and terminal deoxynucleotidyltransferase-mediated deoxyuridine 5'-triphosphate nick-end labeling (TUNEL). Cell-surface TRAIL receptors were measured by flow cytometry. Results: Conditioned culture medium from macrophages isolated from pleural effusions containing 1%-5% tumor cells (CM-A) contained TRAIL at 9801300 pg/mL, whereas that from macrophages from pleural effusions containing more than 50% tumor cells or containing no tumor cells (CM-B) contained TRAIL at 0-50 pg/mL. When cultured with medium containing 50% CM-A, 40% (95% confidence interval [CI] = 30% to 50%) of Colo 205 cells underwent apoptosis; when cultured with 50% CM-B, 8% (95% CI = 3% to 13%) underwent apoptosis. When Colo 205 cells were cultured with 50% CM-A, cell-surface expression of TRAIL death receptors DR5 and DR4 increased 13-fold and sixfold, respectively, compared with that of untreated Colo 205 cells. Recombinant TRAIL induced 90% (95% CI = 85% to 95%) of Colo 205 cells to undergo apoptosis and acted synergistically with TNF-alpha to induce apoptosis. Conclusion: Macrophages from cancer patients appear to be activated by tumor cells to produce TRAIL and to increase the expression of TRAIL death receptors DR4 and DR5 on tumor cells.