The Roles of Bronchial Glands in Airway Defense Mechanisms

Bronchial glands are abundant in human airways, playing a central role in airway secretion and the secretion of mucin, electrolytes and various defensive substances. Both mucin and electrolyte secretions from the bronchial glands maintain an effective mucociliary transport in the airways. Various defensive substances from the bronchial glands include lactoferrin, lysozyme, secretory IgA, secretory leukoprotease inhibitor (SLPI) and surfactant protein A (SP-A). Here, we focused on SLPI and SP-A secretion from human bronchial glands. First, we examined the secretory response and gene expression of SLPI in isolated human glands in response to human neutrophil elastase (HNE). The results indicate that, in human bronchial glands, HNE at low concentrations stimulates SLPI production and secretion, whereas HNE at high concentrations does not. Next, we examined SP-A secretion and gene expression in human bronchial glands. The findings indicate that human bronchial gland cells can transcribe the SP-A2 gene and produce SP-A in a manner different from alveoli, thus playing a role in airway defense mechanisms.