Alveolar macrophages, surfactant lipids, and surfactant protein B regulatethe induction of immune responses via the airways

The influences of alveolar macrophages (AM) and pulmonary surfactant on the induction of immune responses via the airways were assessed. Mice were dep leted of their AM by intratracheal instillation of multilamellar vesicles c ontaining dichloromethylene-diphosphonate followed by intratracheal instill ation of a T cell-dependent antigen, trinitrophenyl-keyhole limpet hemocyan in, in vesicles of various compositions. The primary immune response was de termined in the spleen of these animals using an ELI-Spot assay. The second ary immune responses in the sera of the mice were assessed using enzyme-lin ked immunosorbent assays. An immune response was detected in animals deplet ed of their AM and intratracheally instilled with antigen in small unilamel lar vesicles consisting of either phosphatidylcholine cholesterol or surfac tant lipids. Incorporation of surfactant protein (SP)-B in the antigen vesi cles enhanced the immune response, whereas SP-A or SP-C in the antigen vesi cle did not have an effect. Strikingly, intratracheal instillation of SP-B containing antigen vesicles can induce an immunoglobulin M immune response in mice without depletion of AM. These results indicate that SP-B containin g vesicles can enhance the induction of immune responses via the airways an d further illustrate the important roles of both AM and pulmonary surfactan t in the pulmonary immune system.