Antibacterial components in bronchoalveolar lavage fluid from healthy in individuals and sarcoidosis patients

Antibacterial peptides and proteins are an integral part of the epithelial defense barrier that provides immediate protection against bacterial invasi on. In humans, alpha-defensins are mainly bactericidal effecters in circula ting granulocytes, beta-defensin-1 is synthesized in epithelial cells, and LL-37 is produced in granulocytes but is also induced in skin epithelia dur ing inflammation. To investigate the importance of these defense effectors in disease, we analyzed bronchoalveolar lavage fluid (BALF) for bactericida l activity. Antibacterial activity was found in BALF material from healthy individuals and sarcoidosis patients, with enhanced activity in BALF from t he patients. The activity was present as several antibacterial components, of which we have so far characterized LL-37, lysozyme, cr-defensins, and an tileukoprotease. In addition, the antibacterial peptide LL-37 was located i n alveolar macrophages, bronchial epithelial cells, and bronchial glands, s uggesting that it has a defensive role in airway mucosa. In conclusion, the airway epithelium is protected by a complex antibacterial defense system. This is activated in sarcoidosis, and may explain why these patients seldom develop severe respiratory tract infections.