beta-Defensins are antimicrobial peptides that exert their host-defense 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 these types of activities. In this study we have investigated the interaction of fluorescently labelled human beta defensin 2 (hBD2) with monocytes, macrophages and immature dendritic cells, observing a differential capacity to be rapidly internalised into these cells. Complementary microscopy techniques (TEM, optical and infrared) were used to explore the functional and biological implications of these interactions on immature dendritic cells. Short-term exposure to the peptide resulted in significant alterations in membrane composition and re-organization of the endomembrane system, with induction of degranulation. These events may be associated with the antigen-presenting activities or the chemotaxis of iDC, which appears to occur via both CCR6-dependent and independent mechanisms.
