Identification of hBD-3 in respiratory tract

ABSTRACT: Human b-defensin (hBD)-3, a 45 amino acid antimicrobial peptide, was originally isolated from human skin. hBD-3 mRNA has also been detected in the airways by RT-PCR. While hBD-3 may be involved in antimicrobial defences within the respiratory tract, the presence of hBD-3 peptide in the respiratory system has not yet been confirmed. The antimicrobial activity of the synthesised hBD-3 peptide was measured by a radial diffusion assay and a colony count assay. The present authors confirmed the presence of hBD-3 peptide in homogenates of human lung and serum using reverse-phase HPLC coupled with a highly sensitive RIA. The localisation of the hBD-3 peptide was investigated by immunohistochemistry. In addition, the serum concentrations of hBD-3 were measured by RIA. hBD-3 exhibited a strong antimicrobial activity, which was unaffected by increasing salt concentrations. Immunohistochemically, the current authors observed the expression of hBD-3 in bronchial and bronchiolar epithelial cells. The mean¡SD serum concentration of hBD-3 in patients with bacterial pneumonia was 239.4¡17.8 pg?mL-1 in the acute phase and, decreased to 159.3¡20.1 pg?mL-1 after the completion of therapy. In conclusion, these findings will help elucidate the role of human b-defensin-3 in host immune responses and identify the pathophysiological significance of this molecule in respiratory infections