[Bronchopulmonary antigenic information].

Abstract

Only a small part of those antigenic compounds that pass through the rhinopharyngeal filter and reach the lower airways or the lung crosses the bronchial or alveolar epithelial barrier. The crossing, which is directly or indirectly mediated by macrophage phagocytosis, provides antigenic information which starts off an immune reaction with different impacts on the bronchi and deep lung. Normally (infections excluded), the lung is quiescent, with a probably weak immune activity. In contrast, the level of immune activity in the bronchial lymphoid tissue, although inferior to that of the rhinopharynx, is high. This gradient of immune activity decreasing from the upper airways to the alveoli may be compared to the gradient of saprophytic bacteria which are numerous in the nose, mouth and pharynx, and absent in the deep lung.