ROLLINS-SMITH, L.A.; Vanderbilt Univ. Med. Center: Antimicrobial Peptide Defenses in Amphibian Skin

The skin of amphibians is critical for fluid balance, respiration, and for transport of sodium and other essential ions. It also serves as a barrier to entry of pathogens. One of the natural defenses in the skin is production of antimicrobial peptides in granular glands of the dermal layer. Discharge of the granular glands is initiated by stimulation of sympathetic nerves. Thus, the immune defense of the skin must be intimately connected to other physiological responses. However, very little is known about how neuroendocrine regulation of other skin functions is integrated with production and release of antimicrobial peptides. In an effort to determine whether antimicrobial peptides play an important role in protection from invasive skin pathogens, we have studied the activity of more than 30 purified antimicrobial peptides from amphibians for growth inhibition of the chytrid fungus, Batrachochytrium dendrobatidis, which is associated with global amphibian declines. We have also studied the anti-chytrid activity of peptide mixtures recovered from the skin secretions of other amphibians. The picture that emerges is that most species have one or more antimicrobial peptides with potent activity against the chytrid fungus. Further, there is a general trend to suggest that species with potent mixtures of peptides are more resistant to infection by chytrids than those with less active peptides. Thus, we conclude that antimicrobial peptides produced in the skin are an important defense against skin pathogens and do affect survival of populations. Because many species seem to have a reasonable defense against chytrids and yet suffer population declines that are associated with chytrid infections, it is likely that other factors such as temperature, conditions of hydration, �stress�, or pesticides may alter normal defenses and allow for uncontrolled infection. [Support NSF IBN-9977063; IBN-0131184; DEB-0213851]