2C,D) and ELISA (Fig. 2E,F; Supporting Fig. 3). In contrast, both HCV core-treated and HCV+ hepatocyte cocultured with purified CD33+ cells did not suppress T cells in these culture conditions (Supporting Fig. 4), suggesting that other cells (i.e., CD33− cells) might contribute, in part, to the generation of HCV-mediated MDSCs. We next determined if HCV core-treated Regorafenib order CD33+ cells required cell contact for T-cell suppression. To accomplish this, we cocultured CD33+ cells with T cells as described

above using a transwell plate. As shown in Fig. 3, there was no longer suppression of T-cell proliferation or IFN-γ production by T cells cocultured with HCV core-treated antigen presenting cells. These results suggest that HCV core-mediated inhibition of T-cell responsiveness is dependent

on cell-to-cell contact. Phenotypically, human MDSCs have been described as CD33+CD11b+CD14+ and HLADRlow/−.11 However, CD14 levels have varied depending on the system. We assessed the cell surface expression of CD11b, CD14, and HLA-DR in CD33 selected cells 7 days after HCV core treatment. Relative to β-gal, HCV core-treated CD33+ cells expressed equivalent levels of CD14. Notably, core-treated samples expressed only low levels of CD11b and were HLA-DRlow/− (Fig. 4). Immunomodulatory protein B7-H1 was not up-regulated in HCV core-treated samples (Supporting Fig. 5). MDSCs have been found to suppress T-cell responses through several mechanisms.9 They include metabolism of arginine by arginase-1, increased production Vemurafenib mw of nitric oxide, and ROS. To delineate the mechanism

by which HCV core-treated CD33+ cells suppress autologous T cells, we first assessed the expression of arginase-1, iNOS, and p47phox, a component of the nicotinamide adenine dinucleotide phosphate oxidase (NOX) complex responsible for ROS production in MDSC, by qPCR. PBMCs were treated with HCV core or β-gal for 7 days and lysates for protein and RNA analysis were harvested from CD33+ MCE公司 cells immediately following selection. HCV core-treated CD33+ cells do not up-regulate the expression of arginase-1 or iNOS. Strikingly, the expression of STAT3-inducible p47phox is significantly up-regulated relative to control at both the RNA and protein level (Fig. 5A,B). NOX complex members gp91phox and p22phox were also modestly up-regulated (Supporting Fig. 6). ROS levels were evaluated by loading CD33+ cells with DCFDA. HCV core-treated CD33+ cells demonstrated significantly higher ROS up-regulation following PMA stimulation compared with control (Fig. 5C). Thus, HCV core-treated CD33+ cells may use ROS to suppress T cells. Furthermore, the addition of ROS inactivating enzyme, catalase, significantly restores the proliferative capacity of CD4 and CD8 T cells upon coculture with HCV core-treated CD33+ cells (Fig. 5D; Supporting Fig. 7). The addition of catalase also significantly restores IFN-γ responses (Fig.