Specificity of immunosuppression by human alveolar cells

To study their effect on T- and B-lymphocyte functions, we obtained human alveolar cells, predominantly macrophages, by bronchoalveolar lavage. The cellular target of suppression by alveolar cells of lymphoproliferation was defined by cell separation techniques. THe results indicate a direct effect on T cells by alveolar cells via a soluble mediator released from alveolar cells. In contrast to the profound suppression of mitogen-induced T-cell proliferation, no significant suppression by equivalent numbers of alveolar cells was observed in assays of B-lymphocyte function or in the interactions of helper and suppressor T cells with B lymphocytes. These observations are consistent with an immunoregulatory role for alveolar cells, most likely alveolar macrophages: inhibiting cell-mediated immune responses and delayed hypersensitivity in the lung, while favoring antibody responses.