Innate immune defense of the nail unit by antimicrobial peptides.

BACKGROUND: The nail is susceptible to microbial invasion, yet is usually able to defend itself from infection. This occurs despite isolation from cell-mediated immunity. OBJECTIVE: The aim of this study was to determine whether soluble innate immune molecules are present in the nail environment that can protect against microbial colonization. METHODS: Chromatographic techniques were used to purify cationic antimicrobial molecules from porcine hoof extracts. Sections of human and mouse digits were immunostained with antibodies to each species' cathelicidin antimicrobial peptide. Liquid antimicrobial assays were used to determine the activity of these molecules against relevant pathogens. RESULTS: Human, porcine, and murine nails contain antimicrobial molecules, and the human cathelicidin LL-37 can kill Candida albicans. CONCLUSION: The presence of antimicrobial peptides in nails with activity against relevant nail pathogens may account for the ability of the nail unit to resist infection in the absence of direct access to the cellular immune system.