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Characterizing the interactions between the host defence peptide, LL-37, and lung epithelial cells Lau, Yee-Lar Elaine

Abstract

LL-37 is a human cationic host defense peptide that is a component of innate immunity. In addition to its modest antimicrobial activity, LL-37 affects the behavior of effector cells involved in the innate immune response, including modification of transcriptional responses. However, its mode of interaction with eukaryotic cells remains unclear. In this research study, the interaction of LL-37 with epithelial cells was characterized in tissue culture by using biotinylated LL-37 (LL-37B) and confocal microscopy. LL-37 was actively taken up into A549 human epithelial cells and eventually localized to the perinuclear region. Specific inhibitors were used to demonstrate that the uptake process was not mediated by actin but required elements normally involved in endocytosis, and that trafficking to the perinuclear region was dependent upon microtubules. Using Scatchard analysis, it was revealed that A549 epithelial cells have two receptors for LL-37B, with high and low affinity for LL-37. Further studies, consistent with other publications, that, at higher concentrations, LL-37 demonstrated some cytotoxicity. Therefore the cytotoxic nature of LL-37 was examined in the presence of different sources of serum. LL-37 was cytotoxic in the presence of 10% fetal bovine serum but not 10% human serum and that cytotoxicity led to apoptosis, as assessed by TUNEL assay and Western blot for pro-caspase-3. High density lipoproteins present in human serum, but not the major constituent in HDL, apolipoprotein A-1, inhibited LL-37-induced cytotoxicity. The localization of LL-37B differed according to the type of serum present during incubation. These results suggest that LL-37 interacts directly with epithelial cells and further our understanding of its role in modulating the innate immune response.

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