Enhancement of macrophage and monocyte cytotoxicity by the surface active material of lung lining fluid

The surface active material (SAM) of alveolar lining fluid has been shown to have immunologic activity. We studied the effect of SAM on monocyte-macrophage cytotoxicity against a tumor cell line. Alveolar macrophages were studied from 15 subjects without cancer. Tumor growth, as assessed by tritiated thymidine incorporation, was significantly inhibited by the macrophages alone (tumor alone median 39,401 cpm, macrophages plus tumor median 12,153 cpm, P less than 0.01). Tumor cytotoxicity was enhanced by preincubating the macrophages with lipopolysaccharide (median 37 cpm, P less than 0.01) or coincubating the tumor cells and macrophages with SAM (median 5474 cpm, P less than 0.01). Similar results were seen when using blood adherent mononuclear cells. There was increasing cytotoxicity for the adherent mononuclear cells with increasing amounts of SAM. When the various phospholipids of SAM were studied, it was found that phosphatidylcholine, sphingomyelin, and phosphatidyl glycerol all enhanced adherent mononuclear cell cytotoxicity, whereas phosphatidylinositol inhibited adherent mononuclear cell cytotoxicity. These studies suggest that SAM may have important immunoregulatory function for the alveolar macrophage.