Expression of Fc gamma receptor-mediated phagocytosis by airway intra-luminal macrophages.

Macrophages in the conducting airways of the lower respiratory tract constitute an anatomically defineable subpopulation of pulmonary macrophages. Little information regarding the functional characteristics of the airway intra-luminal macrophages (AI-LM) is currently available. In this study, the AI-LM resident in the trachea and mainstem bronchi of the rat were harvested by an airway lavage technique and the ability of the AI-LM to phagocytize by Fc gamma-receptors was evaluated relative to the phagocytic activities of alveolar macrophages (AM) obtained by bronchoalveolar lavage. More than 60% of the AI-LM phagocytized sheep erythrocytes opsonized with IgG (SRBC-IgG) and the distributions of the engulfed SRBC-IgG in the phagocytic AI-LM were virtually identical to those in AM. The AI-LM may represent AM that have been translocated from the alveolar space compartment to the conducting airways; it remains possible, however, that at least some of the AI-LM may have an airway origin. Regardless, the results of our phagocytic studies suggest AI-LM may functionally provide a protective phagocytic role in the conducting airways.