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Apoptosis of Airway Epithelial Cells

Human Serum Sensitive Induction by the Cathelicidin LL-37

Department of Microbiology and Immunology, University of British Columbia, Vancouver, British Columbia, Canada

Correspondence and requests for reprints should be addressed to Dr. R. E. W. Hancock, Centre for Microbial Diseases and Immunity Research, Room 232, 2259 Lower Mall Research Station, University of British Columbia, Vancouver, BC, V6T 1Z4 Canada. E-mail: bob{at}cmdr.ubc.ca

LL-37 is a human cationic host defense peptide that is present in the specific granules of neutrophils, produced by epithelial cells from a variety of tissues, and is upregulated during inflammation, infection, and injury. It has been proposed to have a variety of antimicrobial functions, including both direct antimicrobial activity and immunomodulatory functions. Using the TUNEL assay it was demonstrated that LL-37 induced apoptosis in vitro in the A549 human lung and 16HBE4o- human airway epithelial cell lines, and in vivo in the murine airway. Peptide-induced apoptosis in vitro involved the activation of caspase pathways and was substantially inhibited by an inhibitor of caspase 3. Apoptosis was also inhibited by human serum, but not fetal bovine serum. Similarly, human but not fetal bovine serum inhibited the cellular internalization of LL-37 and the production of IL-8 in response to LL-37 treatment of epithelial cells. The protective effects of human serum were also observed with high-density lipoproteins but not by the core peptide apolipoprotein A1, providing one possible mechanism of human serum inhibition of apoptosis. We propose that LL-37–induced apoptosis of epithelial cells at low serum tissue sites may have a protective role against bacterial infection.

Key Words: apoptosis • cathelicidin • epithelial cells • host defense peptide • LL-37

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