Immune functions of murine alveolar macrophages: binding of lymphocytes and support of lymphocyte proliferation

Interactions between alveolar macrophages and lymphocytes may be important in the generation of pulmonary immune responses or in the induction of immunologic lung disease. We compared the relative abilities of normal murine alveolar macrophages and peritoneal macrophages to bind primed lymphocytes and to support antigen-induced lymphocyte proliferation. Alveolar macrophages were obtained by lung lavage and peritoneal macrophages by peritoneal lavage of normal mice. Lymph-node cells were harvested from draining lymph nodes of mice immunized with the peptide antigen (T,G)-A-L. Lymph-node cells were depleted of macrophages by passage through columns of Sephadex G-10 and nylon wool. To study the binding of lymphocytes to macrophages, lymph-node cells were layered over antigen-pulsed alveolar and peritoneal macrophage monolayers and the number of lymphocytes bound to the macrophages counted microscopically after incubation for 1-20 hr. Macrophage support of antigen-induced lymphocyte proliferation was studied by 3H-thymidine uptake of macrophage-depleted primed lymph-node cells cultured in the presence of soluble antigen. Cultures were repleted with graded percentages of alveolar or peritoneal macrophages. The results showed that alveolar macrophages bound significantly fewer lymphocytes than peritoneal macrophages both in a nonspecific and an antigen-specific manner. The difference in lymphocyte-binding affinity between the two macrophage types could not be attributed to factors present in lung lavage fluid. Results of the lymphocyte proliferation studies showed that while alveolar macrophages were able to support lymphocyte proliferation in response to antigen, they did so less effectively than an equal number of peritoneal macrophages. We conclude that alveolar macrophages differ significantly from peritoneal macrophages in their ability to interact with lymphocytes, both with respect to lymphocyte binding and in support of lymphocyte proliferative responses.