Our observations regarding the temperature-dependent extent and location of vesicle-associated fluorescence in host cells and decreased fluorescence in host cells upon pretreatment with methyl-β-cyclodextrin (which disrupts caveolae, lipid rafts, as well as Combretastatin A4 in vivo clathrin-coated

pit-mediated entry pathways) suggested that S470 vesicles were also internalized. In contrast to other examples of internalized vesicles, P aeruginosa vesicles appear to enter host cells via multiple pathways. Hypertonic media, which impairs clathrin coated pit formation, did significantly decrease vesicle internalization and some surface-bound vesicles were found colocalized with clathrin. However, neither treatment with filipin, which disrupts lipid rafts, nor chlorpromazine, which blocks clathrin-coated pits, decreased vesicle internalization significantly. It should also be considered that P. aeruginosa vesicles could JNJ-26481585 fuse with the epithelial cells and that vesicle membrane components are subsequently internalized

by plasma membrane trafficking while lumenal components are liberated into the host cell cytosol. Evidence of fusion of vesicles with the plasma membrane has been presented for Actinobacillus actinomycetemcomitans vesicles [13]: Confocal microscopy of HL60 cells coincubated with these vesicles showed immediate and strong labelling, primarily at the plasma membrane. We did not observe strong perimeter labelling of host cells with P. aeruginosa vesicles (Fig 2B). In fact, when we blocked active transport with hypertonic sucrose, we found a significant decrease in vesicle-associated fluorescence, not accumulation

of fluorescence at the cell periphery (Fig 3E). Thus, our data support a model where P. aeruginosa vesicles do not fuse to the plasma membrane, but instead bind and are internalized. We observed an increase in human lung epithelial cell-associated fluorescence over time. This MRT67307 nmr result is consistent with either vesicle ADP ribosylation factor attachment causing receptor upregulation, or continuous vesicle binding, internalization, recycling of vesicle receptors to the cell surface. These characteristics are similar to the behavior of enterotoxigenic E. coli vesicles with intestinal epithelial cells [14]. Further experiments using different inhibitors, markers, and cell lines, will be necessary to definitively identify the host cell factors critical to P. aeruginosa vesicle entry. In relation to CF-related research, it would be particularly interesting to see whether the interactions depend on functional and properly localized CFTR. Ceramide-rich rafts containing clusters of the CFTR and CD95 have been implicated as the means for internalization of whole P. aeruginosa. These rafts are disrupted by MβCD, and thus in light of our MβCD treatment results, they present a potential route for vesicle internalization [35].