Mouse β-Defensin 3 Is an Inducible Antimicrobial Peptide Expressed in the Epithelia of Multiple Organs

<jats:title>ABSTRACT</jats:title> <jats:p> One component of host defense at mucosal surfaces is epithelium-derived peptides with antimicrobial activity called defensins. We describe in this report the isolation and characterization of a murine homologue of human β-defensin 2 (hBD-2) called mouse β-defensin 3 (mBD-3). The predicted amino acid sequence shows the hallmark features of other known epithelial defensins, including the ordered array of six cysteine residues. Analysis of a genomic clone of mBD-3 revealed two exons separated by a 1.7-kb intron. The mBD-3 gene is localized at the proximal portion of chromosome 8, the site where genes for mouse α- and β-defensins are found. Under basal condition, mBD-3 transcripts were detected at low levels in epithelial cells of surface organs, such as the intestine and lung. After instillation of <jats:italic>Pseudomonas aeruginosa</jats:italic> PAO1 into mouse airways, mBD-3-specific mRNA was upregulated significantly not only in large airways but also in the small bowel and liver. Recombinant mBD-3 peptide, produced from a baculovirus expression system, showed antimicrobial activity against <jats:italic>P. aeruginosa</jats:italic> PAO1 (MIC of 8 μg/ml) and <jats:italic>Escherichia coli</jats:italic> D31 (MIC of 16 μg/ml) in a salt-dependent manner. This study demonstrates that a murine homologue of hBD-2 is present in the respiratory system and other mucosal surfaces. These similarities between murine and human host defense apparatus provide further impetus to evaluate the mouse as a model for studying the human innate host defense system. </jats:p>