Cationic antimicrobial peptides (APs) are produced at mucosal surfaces and play a key role as a first line of defense against infection. To understand how APs might impact disease progression in otitis media (OM), our goal was to identify and characterize APs expressed by the epithelium lining the uppermost airway of the chinchilla, the established rodent host for the study of the bacterial-viral pathogenesis in OM. Using a molecular approach, we cloned a cDNA encoding a homolog of human 13-defensin 3, designated chinchilla 13-defensin-1 (cBD-1), and found by Northern analysis expression of the corresponding mRNA in nasopharyngeal and tongue mucosae as well as skin. By reverse transcription-PCR, cBD-1 mRNA was also detected in RNA isolated from trachea, lung, and Eustachian tube tissues. The predicted mature form of cBD-1, expressed as a recombinant peptide in Escherichia coli, demonstrated bactericidal activity against the three primary opportunistic pathogens of OM as well as Candida albicans. Continued study of this and other APs will allow us to determine their role in bacterial colonization of the upper airway as well as how viruses might contribute to the pathogenesis of OM by modulating AP expression.
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