Effects on antigen-presenting cells of short-term interaction with the human host defence peptide ß-defensin 2.

ß-Defensins are antimicrobial peptides that exert their host-defence functions at the interface between the host and microbial biota. They display a direct, salt- and medium-sensitive cidal activity, in vitro, against a broad spectrum of bacteria and fungi, and there is increasing evidence that they also play a role in alerting and enhancing cellular components of innate and adaptive immunity. Their interaction with biological membranes plays a central role in both of these types of activities. In the present study, we have investigated the interaction of fluorescently labelled hBD2 (human ß-defensin 2) with monocytes, macrophages and iDCs (immature dendritic cells), observing a differential capacity to be rapidly internalized into these cells. Complementary microscopy techniques [TEM (transmission electron microscopy), optical microscopy and IR microspectroscopy] were used to explore the functional and biological implications of these interactions on iDCs. Short-term exposure to the peptide resulted in significant alterations in membrane composition and re-organization of the endomembrane system, with the induction of degranulation. These events may be associated with the antigen-presenting activities or the chemotaxis of iDCs, which appears to occur via both CCR6 (CC chemokine receptor 6)-dependent and -independent mechanisms.

Artificial beta-defensin based on a minimal defensin template.

We have designed and chemically synthesized an artificial beta-defensin based on a minimal template derived from the comparative analysis of over 80 naturally occurring sequences. This molecule has the disulfide-bridged beta-sheet core structure of natural beta-defensins and shows a robust salt-sensitive antimicrobial activity against bacteria and yeast, as well as a chemotactic activity against immature dendritic cells. An SAR (structure-activity relationship) study using two truncated fragments or a Cys-->Ser point-mutated analogue, from which one or two of the three disulfide bridges were absent, indicated that altering the structure resulted in a different type of membrane interaction and a switch to different modes of action towards both microbial and host cells, and that covalent dimerization could favour antimicrobial activity. Comparison of the structural, aggregational and biological activities of the artificial defensin with those of three human beta-defensins and their primate orthologues provided useful information on how their mode of action may relate to specific structural features.