Lung derived surface active material (SAM) inhibits natural killer cell tumor cytotoxicity

Natural killer cells have been identified in lung tissue but have been found to have significantly less tumor cytotoxicity than natural killer cells found elsewhere in the body. The natural killer cells in the lung are still functional, since their killing can be enhanced by Interleukin-2. The surface active material (SAM) of lung lining fluid has been shown to have immunomodulating activity, including the suppression of lymphocyte blast transformation and enhancement of macrophage tumor cytotoxicity. We studied the effect of SAM purified from lung lining fluid on natural killer cell tumor cytotoxicity. SAM markedly inhibited tumor killing (Percent cytotoxicity of cells alone: 41 +/- 7.3% (mean +/- SEM); cells plus SAM: 10 +/- 9.7%, p less than 0.02). Further studies demonstrated that some phospholipids, including phosphatidylcholine, the major phospholipid of SAM, also significantly inhibited natural killer cell tumor killing. This inhibition of natural killer cell tumor cytotoxicity could be reversed by the addition of Interleukin-2 to the natural killer cells. These studies demonstrated that the surfactant found in lung lining fluid significantly inhibited natural killer cell tumor cytotoxicity and this effect could be reversed by Interleukin-2.