Localization of antimicrobial peptides in the tunic of Ciona intestinalis ( Ascidiacea, Tunicata) and their involvement in local inflammatory-like reactions

Tunicates comprising a wide variety of different species synthesize antimicrobial peptides as importanteffector molecules of the innate immune system. Recently, two putative gene families coding forantimicrobial peptides were identified in the expressed sequence tag database of the tunicate Cionaintestinalis. Two synthetic peptides representing the cationic core region of one member of each of thefamilies displayed potent antibacterial and antifungal activities. Moreover, the natural peptides weredemonstrated to be synthesized and stored in distinct hemocyte types. Here, we investigated thepresence of these natural peptides, namely Ci-MAM-A and Ci-PAP-A, in the tunic of C. intestinalisconsidering that the ascidian tunic is a body surface barrier exposed to constant microbial assault.Furthermore, as the tunic may represent a major route of entry for pathogen invasion after its damagewe monitored the location of these peptides upon a local inflammatory-like reaction induced byinjection of foreign cells. Using immunocytochemistry and electron microscopy both peptides werelocalized to the tunic and were massively present in granulocytes of inflamed tissue. Conclusively,antimicrobial peptides may constitute a chemical barrier within the tunic of urochordates.