Alveolar macrophages down-regulate local pulmonary immune responses against intratracheally administered T-cell-dependent, but not T-cell-independent antigens.

The role of alveolar macrophages in the pulmonary immune response against various antigens was studied after elimination of alveolar macrophages by intratracheal administration of liposome-encapsulated dichloromethylene diphosphanate. When the responses against T-cell-independent type 1 and type 2 antigens were compared, it was found that elimination of alveolar macrophages had no effect on T-cell-independent antigens. Intratracheal antigen administration resulted in low lung associated, local responses, although some response was observed in the spleen. In contrast, elimination of alveolar macrophages resulted in an increase in local pulmonary immune response against T-cell-dependent antigens. We conclude from these experiments that alveolar macrophages play an important role in controlling the local pulmonary immune response against T-cell-dependent antigens by down-regulation of local T-cell populations. The alveolar macrophages do not down-regulate the response against intratracheally administered T-cell-independent antigens, although they are important in the protection against inflammatory damage caused by bacterial endotoxins.