Antitumor activities of pleural cavity macrophages (PCM) and pleural cavity lymphocytes (PCL) in lung cancer patients were examined. The effect of coculture supernatants of PCL and autologous tumor cells on the cytostatic activity of macrophages was also examined. Cytostatic activity of PCM was not affected by an advance of metastasis to regional lymph nodes or increase of tumor size and difference of histological type. However, the cytostatic activity of PCM was markedly augmented when pleural invasion was limited to within the visceral pleura although it was low when pleural invasion was absent or extended beyond the visceral pleura. On the other hand, PCL did not exert any cytolytic activity against various tumor target cells. However, coculture supernatants of PCL and autologous tumor cells exhibited the activity of macrophage-activating factor against guinea pig peritoneal macrophages. Furthermore, the higher the cytostatic activity of PCM, the higher the macrophage-activating factor activity of the coculture supernatant of PCL and autologous tumor cells was. These results suggested that antitumor activity of PCM was controlled by specifically sensitized PCL through lymphokines.

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