The synthesis of antimicrobial peptides in the skin of Rana esculenta is stimulated by microorganisms

Secretions of amphibian skin glands contain numerous antimicrobial peptides that play a crucial role in the defense against microorganisms. The location of these glands on the surface of the animal makes them a useful model for in vivo studies of the relationships between the innate immune system and the natural flora. Here, we present the results of a study showing that in Rana esculenta the total antimicrobial activity of skin secretion is modulated by the presence of the natural flora. Frogs kept in a sterile environment do not produce antimicrobial peptides. This finding represents the first in vivo demonstration of the induction of defense peptides in a vertebrate. We also present data on the morphological changes in skin glands of animals kept in sterile conditions or treated with glucocorticoids. Cells from glands regenerated under normal conditions, but not those from "sterile" frogs, contain kappaB-binding activity in the cytoplasm.