Mucoid Pseudomonas aeruginosa , TNF- α , and IL-1 β , but Not IL-6, Induce Human β -Defensin-2 in Respiratory Epithelia

Abstract

Cultured lung epithelial cells release antibacterial activity upon contact with Pseudomonas aeruginosa (PA), which is impaired in cystic fibrosis (CF). In order to identify the factors responsible for killing PA by a biochemical approach, we purified antimicrobial activity from supernatants of the A549 lung epithelial cell line, previously stimulated with PA bacteria, by subsequent high performance liquid chromatography. NH(2)-terminal sequencing of a major bactericidal compound revealed it to be identical with human beta-defensin-2 (hBD-2). A mucoid phenotype of PA, but not two nonmucoid PA strains, high concentrations (> 10 microg/ml) of PA lipopolysaccharide, tumor necrosis factor alpha, and interleukin (IL)-1beta, but not IL-6, dose-dependently induced hBD-2 messenger RNA in cultured normal bronchial, tracheal, as well as normal and CF-derived nasal epithelial cells. Genomic analysis of hBD-2 revealed a promoter region containing several putative transcription factor binding sites, including nuclear factor (NF) kappaB, activator protein (AP)-1, AP-2, and NF-IL-6, known to be involved in the regulation of inflammatory responses. Thus, hBD-2 represents a major inducible antimicrobial factor released by airway epithelial cells either on contact with mucoid PA or by endogenously produced primary cytokines. Therefore, it might be important in lung infections caused by mucoid PA, including those seen in patients with CF.