Antigen presentation by guinea pig alveolar macrophages

The role of alveolar macrophages (MΦ) in the induction of immune responses within the lung was investigated. Guinea pig alveolar MΦ obtained from bronchoalveolar cells (BAC) were found to function as well as peritoneal exudate MΦ 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 MΦ is an effective antigen-presenting cell. 1) Washed alveolar MΦ, previously 'pulsed' with antigen, replaced both soluble antigen and BAC in the stimulation of immune LNL. 2) The interaction of alveolar MΦ over 80% of which were Ia positive, with lymphocytes was genetically restricted, i.e., only antigen-pulsed alveolar MΦ that shared I region-encoded antigens with the antigen-specific T lymphocytes stimulated their proliferation. Furthermore, removal of Ia-positive alveolar MΦ abrogated this response. 3) antigen-pulsed alveolar MΦ specifically bound immune T lymphocytes. In contrast, no evidence was obtained for immunosuppression by alveolar MΦ. Thus, alveolar MΦ failed to suppress specific LNL proliferation even at ratios of alveolar MΦ to LNL of greater than 20:1, ratios that often exist locally within the lung. The possible role of antigen-bearing alveolar MΦ in inducing local immunity and also in focusing a systemic response are discussed.