Isolation of an antibacterial peptide from human lung lavage fluid

The contribution of extracellular secretions to the antibacterial defenses of the lungs remains poorly defined. Recent studies have demonstrated that mouse and rabbit bronchoalveolar washings contain a low-molecular-weight peptide that has antibacterial activity against Escherichia coli. In this study we investigated whether a similar peptide could be identified in human secretions. Bronchoalveolar lavage fluid was obtained from normal volunteers and patients with interstitial lung disease or pulmonary alveolar proteinosis. Cellular material and surfactant lipids were removed from the fluid by sequential centrifugations, and the supernatant was fractionated by exclusion filtration to isolate peptides with a molecular weight less than 10,000. Gel filtration chromatography separated the ultrafiltrate into several peaks, the first of which had antibacterial activity against E. coli. This material was further separated into several hydrophilic peaks by reverse-phase high-pressure liquid chromatography (RPHPLC). All samples had similar RPHPLC graphs. Material from the third RPHPLC peak produced an antibacterial effect similar to that produced by the rabbit and mouse peptide.