Innate Defense of Nails (Abstract)
Richard Gallo MD PhD
Dermatology Online Journal 7(2): 21A

The skin and other epithelial surfaces have recently been found to produce small proteins that kill bacteria and fungi. These antimicrobial peptides represent an innate defense system for protection against infection before cell-mediated adaptive immunity is activated. In lower organisms, this innate defense system is the primary system for protection against infection. In humans, antimicrobial peptides have been discovered in the skin, gut, renal system and blood where they can inhibit microbial growth prior to initiation of cell mediated immunity. We hypothesized that nails must also contain an innate defense system due to the inability of cells of the immune system to penetrate the nail plate and the frequent microbial exposure of this organ. To begin to identify the innate defense system of the nail, extracts of porcine hoof were tested for their inability to inhibit the growth of potential pathogens. Potent antimicrobial activity against was detected. Subsequent purification of this antimicrobial found that the predominant bioactive molecule is small (<1000 MW) and cationic, but not a host derived peptide. Rather, the majority of antimicrobial activity in the nail plate can be duplicated from extracts of resident microflora. This finding suggests at least part of innate nail defense derives from a symbiotic relationship with resident flora. To further explore innate immune function in the nail, mice were used to survey for known antimicrobials. Staining for the antimicrobial peptide CRAMP demonstrated that epithelial cells in the distal phalanges and nail bed constitutively express this peptide while normal epidermal cells of the trunk do not. Thus, two potentially complementary innate defense mechanisms have been defined in mammalian nail structures. A better understanding of this system offers a new approach to understanding nail disease and alternative forms of therapy.

© 2001 Dermatology Online Journal