Antitumour potential of pleural cavity macrophages in lung cancer patients without malignant effusion.

The present study was undertaken to examine whether the presence of primary lung cancer could affect the antitumour activities of pleural cavity macrophages (PCM) and peripheral blood monocytes (PBM). PCM by pleural lavage and PBM were simultaneously obtained from 14 lung cancer patients not showing invasion of the pleural cavity. PCM and PBM were isolated by percoll gradient centrifugation and adherence. The lavage method yielded about 16.8 +/- 9.6 (s.e.) x 10(6) cells, which consisted of 80.7% PCM, 17.6% lymphocytes and 1.6% other cells. The cytotoxic activities of PCM and PBM against allogeneic melanoma (A375) cells were assessed by a 72h 125I-IUdR release assay. The lavaged PCM showed spontaneously high tumour cytotoxic activity which was dependent on the effector/target ratio. In 13 out of 14 cancer patients, PCM were significantly more cytotoxic to melanoma cells than PBM. In contrast, there were no significant differences in production of tumour necrosis factor (TNF-alpha) or interleukin 1 (IL-1) between PCM and PBM. When the abilities of PCM and PBM of the same patient to produce these monokines were compared, PCM produced much more TNF-alpha than PBM, thus indicating a correlation between the expression of spontaneous macrophage-mediated cytotoxicity and spontaneous TNF-alpha production by PCM. These results suggest that PCM may play an important role in host defence against invasion of the pleural cavity by cancer cells.