Antigen presentation by guinea pig alveolar macrophages.

The role of alveolar macrophages (M phi) in the induction of immune responses within the lung was investigated. Guinea pig alveolar M phi obtained from bronchoalveolar cells (BAC) were found to function as well as peritoneal exudate M phi in supporting proliferation of purified lymph node lymphocytes (LNL) induced by both soluble antigens and mitogen (Con A). Several lines of evidence indicate that the alveolar M phi is an effective antigen-presenting cell. 1) Washed alveolar M phi, previously "pulsed" with antigen, replaced both soluble antigen and BAC in the stimulation of immune LNL. 2) The interaction of alveolar M phi, over 80% of which were Ia positive, with lymphocytes was genetically restricted, i.e., only antigen-pulsed alveolar M phi that shared I region-encoded antigens with the antigen-specific T lymphocytes stimulated their proliferation. Furthermore, removal of Ia-positive alveolar M phi abrogated this response. 3) Antigen-pulsed alveolar M phi specifically bound immune T lymphocytes. In contrast, no evidence was obtained for immunosuppression by alveolar M phi. Thus, alveolar M phi failed to suppress specific LNL proliferation even at ratios of alveolar M phi to LNL of greater than 20:1, ratios that often exist locally within the lung. The possible role of antigen-bearing alveolar M phi in inducing local immunity and also in focusing a systemic response are discussed.