Human alveolar macrophages suppress the proliferative response of peripheral blood lymphocytes

Human alveolar cells were isolated from bronchopulmonary lavage fluids obtained from patients undergoing clinically indicated bronchoscopy. Alveolar cells strongly suppressed the proliferation of peripheral blood lymphocytes in response to mitogens and antigens. Separation of the alveolar cells into adherent and nonadherent fractions indicated that the suppression was mediated by the adherent cells, or alveolar macrophages. Indomethacin at least partially relieved suppression, suggesting the involvement of prostaglandin synthesis. The suppression could be duplicated by supernatants obtained from unstimulated cultures of alveolar cells. Some specificity of suppression was apparent, in that not all proliferating cells were suppressed. T lymphocytes may be more readily suppressed than B lymphocytes, and the most susceptible cells may be a subpopulation of T lymphocytes.