Immunolocalization of a beta-defensin (Tu-BD-1) in the skin and subdermal granulocytes of turtles indicate the presence of an antimicrobial skin barrier

The resistance of turtle skin to infections is likely due to the production of a thick corneous layer but also of soluble antimicrobial molecules released in the stratum corneum. The present study has determined the localization of beta-defensin peptides previously identified by biomolecular analysis in turtle skin. After the production of a specific antibody for one peptide indicated as Ts-BD-1, light and ultrastructural localization indicates that the peptide is mainly present in some variably dense primary granules of granulocytes. These cells are sparse in the connective tissues and within blood vessels present in the dermis and subdermal inter-muscular connective tissue. A weak labeling is also present in the epidermis, especially localized in sparse secretory granules discharged among corneocytes of the stratum corneum. This localization suggests that antimicrobial peptides are common constituents of the narrow extracellular spaces located among superficial corneocytes where bacteria or their remnants are frequently detected. The study suggests that turtle beta-defensins are mainly contained in granulocytes involved in the immunological surveillance of the skin and that they become active after skin wounding.