Immunomodulatory effects of pulmonary surfactant on natural killer cell and antibody-dependent cytotoxicity

Alveolar natural killer (NK) cells are functionally weak compared to their blood and interstitial counterparts. Having previously demonstrated that pulmonary surfactant suppresses lymphocyte responses to a variety of stimuli we sought in this study to determine if surfactant exerts a similar suppressive effect on cytotoxic function. Lipids were purified from the bronchoalveolar lavage (BAL) fluid from normal human volunteers. Human peripheral blood lymphocytes (n = 10 subjects) were cultured overnight in the presence or absence of purified BAL lipids (0.2 mg/ml), or pure preparations of phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylglycerol (PG) (0.4 mg/ml). Standard NK and antibody-dependent cytotoxicity (ADCC) assays were performed using K562 and Chang target cells. The pooled BAL lipids significantly suppressed both NK (P less than 0.01) and ADCC (P = 0.01) activity in a dose-dependent manner. Whereas pure PC did not exert a significant effect, PG significantly suppressed (P less than 0.01) and PE significantly enhanced (P less than 0.01) both cytotoxic functions. There was no change in the expression of leu 7 or 11b antigens by lymphocytes after culture in BAL lipids. These results suggest that under normal circumstances pulmonary surfactant may suppress alveolar cytotoxic responses but that imbalances in the phospholipid profile might affect this immunoregulatory property.