[Secretory immunity of the airways]

Continuous exposure of the respiratory tract to inhaled particles and microbes implies the presence of effective defence mechanisms at a bronchial and alveolar level.

Among the mechanisms involved secretory mucosal immunity contributes considerably to the defence of the bronchial tree. This immunity depends essentially on the active trans-epithelial transport of IgA involved in both innate non-specific and acquired specific immunity. Recently an IgA receptor has been identified on the surface of phagocytes including alveolar macrophages, establishing a link between alveolar and bronchial defences.

The respiratory mucosa represents a crucial interface between the host and its environment, and should provide in the future a new target for the development of diagnostic and therapeutic tools.

Beyond its function as an anatomical barrier the bronchial epithelium possesses a secretory activity that is essential for the protection of the lung. Despite a better understanding of mucosal immunity this secretory activity and in particular the part played by IgA remains to be elucidated.