The human cationic antimicrobial protein (hCAP18), a peptide antibiotic, is widely expressed in human squamous epithelia and colocalizes with interleukin-6

Peptide antibiotics are widespread in nature and, by providing a rapid firs t line of defense, may be key players in the innate immune system. Although epithelia are the main barriers shielding the internal environment from mi croorganisms, the role for peptide antibiotics in epithelial protection is unclear. We recently reported that the human cationic antimicrobial protein hCAP18, the precursor of the antimicrobial peptide called LL-37, is not ex pressed by normal human keratinocytes but is induced in various inflammator y skin disorders. In the present study we demonstrate that hCAP18 is consis tently expressed at both mRNA and protein levels in squamous epithelia of t he mouth, tongue, esophagus, cenix, and vagina in humans. The gene for hCAP 18 contains promoter elements that are potentially regulated by interleukin -6, and our data further show a colocalization between interleukin-6 and hC AP18 expression in these tissues. Our finding that hCAP18 is widely produce d in squamous epithelia suggests a role for this peptide in epithelial anti microbial defense. Furthermore, colocalization with interleukin-6 indicates a potential local mechanism for the upregulation of hCAP18 at the epitheli al surfaces.