Exosomes, nano-sized secreted extracellular vesicles (EVs), are actively studied for their diagnostic and therapeutic potential. In particular, exosomes secreted by dendritic cells (DCs) have been shown to carry MHC-peptide complexes allowing efficient activation of T lymphocytes, thus displaying potential as promoters of adaptive immune responses. DCs also secrete other types of EVs of different size, subcellular origin and protein composition, whose immune capacities have not been yet compared to those of exosomes. Here, we show that large EVs (lEVs) released by human DCs are as efficient as small EVs (sEVs), including exosomes, to induce CD4 T-cell activation When released by immature DCs, however, lEVs and sEVs differ in their capacity to orient T helper (Th) cell responses, the former favouring secretion of Th2 cytokines, whereas the latter promote Th1 cytokine secretion (IFN-γ). Upon DC maturation, however, these functional differences are abolished, and all EVs become able to induce IFN-γ. Our results highlight the need to comprehensively compare the functionalities of EV subtypes in all patho/physiological systems where exosomes are claimed to perform critical roles.

The endogenous estradiol metabolite estradiol 17␤-D-glucuronide (E 2 17G) induces an acute cholestasis in rat liver coincident with retrieval of the canalicular transporters bile salt export pump (Bsep, Abcc11) and multidrug resistance-associated protein 2 (Mrp2, Abcc2) and their associated loss of function. We assessed the participation of Ca 2؉ -dependent protein kinase C isoforms (cPKC) in the cholestatic manifestations of E 2 17G in perfused rat liver (PRL) and in isolated rat hepatocyte couplets (IRHCs). In PRL, E 2 17G (2 mol/liver; intraportal, single injection) maximally decreased bile flow, total glutathione, and [ 3 H] taurocholate excretion by 61%, 62%, and 79%, respectively; incorporation of the specific cPKC inhibitor Gö6976 (500 nM) in the perfusate almost totally prevented these decreases. In dose-response studies using IRHC, E 2 17G (3.75-800 M) decreased the canalicular vacuolar accumulation of the Bsep substrate cholyl-lysylfluorescein with an IC50 of 54.9 ؎ 7.9 M. Gö6976 (1 M) increased the IC50 to 178.4 ؎ 23.1 M, and similarly prevented the decrease in the canalicular vacuolar accumulation of the Mrp2 substrate, glutathione methylfluorescein. Prevention of these changes by Gö6976 coincided with complete protection against E 2 17G-induced retrieval of Bsep and Mrp2 from the canalicular membrane, as detected both in the PRL and IRHC. E 2 17G also increased paracellular permeability in IRHC, which was only partially prevented by Gö6976. The cPKC isoform PKC␣, but not the Ca 2؉ -independent PKC isoform, PKC⑀, translocated to the plasma membrane after E 2 17G administration in primary cultured rat hepatocytes; Gö6976 completely prevented this translocation, thus indicating specific activation of cPKC. This is consistent with increased autophosphorylation of cPKC by E 2 17G, as detected via western blotting. Conclusion: Our findings support a central role for cPKC isoforms in E 2 17G-induced cholestasis, by inducing both transporter retrieval from the canalicular membrane and opening of the paracellular route. (HEPATOLOGY 2008;48:1885-1895 B ile formation represents a key liver function by which xenobiotics and endogenous metabolites such as cholesterol, bilirubin, and hormones are eliminated from the body. 1,2 Efflux of solutes by adenosine triphosphate-dependent transporters at the canalicular membrane of hepatocytes provide the driving force for osmotic bile formation; among these transporters, the bile salt export pump (Bsep, Abcc11) and multidrug re-

Carpier et al. show that LAT trafficking to the immune synapse depends on endosome-to-Golgi/TGN retrograde transport and is controlled by Rab6 and Syntaxin-16. Moreover, they show that this retrograde pathway controls the TCR-induced activation of T lymphocytes.