Loss of lymphocyte modulatory control by surfactant lipid extracts from acute hypersensitivity pneumonitis: comparison with sarcoidosis and idiopathic pulmonary fibrosis.

Surfactant components are recognized to exert a regulatory control on lymphocytes in physiological conditions, as testified by in vitro studies. However, what happens following lung injury has not been established. As surfactant composition is altered in interstitial lung diseases, this work was carried out to compare the modulatory impact of normal human alveolar fluids on lymphocyte proliferation, with that from inflammatory lung diseases which are characterized by distinct patterns of immunologically-mediated alterations (i.e. sarcoidosis, acute hypersensitivity pneumonitis, idiopathic pulmonary fibrosis). Thymidine incorporation of allogeneic normal human blood lymphocytes was studied in the presence of total alveolar fluids or lipid extracts from 37 subjects, and phytohaemagglutinin (PHA) as T-cell mitogen. The results show that: 1) total alveolar fluids and lipid extracts from normal subjects share a concentration-dependent suppressive activity on T-cell proliferation; 2) total alveolar fluids from diseased patients have lost this property, either by a lack of suppressive activity (i.e. idiopathic pulmonary fibrosis) or even by enhanced activity (i.e. sarcoidosis and hypersensitivity pneumonitis); 3) lipid extracts from diseased patients still retain the suppressive activity of normal subjects, except for hypersensitivity; and 4) an imbalance in surfactant phospholipids with an increase in the inducers to suppressors ratio is more likely to explain this alteration in hypersensitivity pnuemonitis than changes in total lipid content. In conclusion, alveolar lipid extracts from acute hypersensitivity pnuemonitis have lost the modulatory control normally exerted by surfactant lipids on lymphocyte proliferation in vitro. This alteration may contribute to the invasion of the lung by lymphocytes in acute hypersensitivity pnuemonitis in vivo.