Chronic hepatitis B virus (HBV) infection is caused by inadequate anti-viral immunity. Activation of plasmacytoid dendritic cells (pDC) leading to IFNα production is important for effective anti-viral immunity. Hepatitis B virus (HBV) infection lacks IFNα induction in animal models and patients and chronic HBV patients display impaired IFNα production by pDC. Therefore, HBV and HBV-derived proteins were examined for their effect on human pDC in vitro. In addition, the in vitro findings were compared to the function of pDC derived from chronic HBV patients ex vivo. In contrast to other viruses, HBV did not activate pDC. Moreover, HBV and HBsAg abrogated CpG-A/TLR9-induced, but not Loxoribine/TLR7-induced, mTOR-mediated S6 phosphorylation, subsequent IRF7 phosphorylation and IFNα gene transcription. HBV/HBsAg also diminished upregulation of co-stimulatory molecules, production of TNFα, IP-10 and IL-6 and pDC-induced NK cell function, whereas TLR7-induced pDC function was hardly affected. In line, HBsAg preferentially bound to TLR9-triggered pDC demonstrating that once pDC are able to bind HBV/HBsAg, the virus exerts its immune regulatory effect. HBV not only directly interfered with pDC function, but also indirectly by interfering with monocyte-pDC interaction. Also HBeAg diminished pDC function to a certain extent, but via another unknown mechanism. Interestingly, patients with HBeAg-positive chronic hepatitis B displayed impaired CpG-induced IFNα production by pDC without significant alterations in Loxoribine-induced pDC function compared to HBeAg-negative patients and healthy controls. The lack of activation and the active inhibition of pDC by HBV may both contribute to HBV persistence. The finding that the interaction between pDC and HBV may change upon activation may aid in the identification of a scavenging receptor supporting immunosuppressive effects of HBV and also in the design of novel treatment strategies for chronic HBV.

The immunostimulatory role of Kupffer cells in various inflammatory liver diseases is still not fully understood. In this study, phenotypic and functional aspects of Kupffer cells from healthy C57BL/6 mice were analyzed and compared with those of splenic and peritoneal macrophages to generate a blueprint of the cells under steady-state conditions. In the mouse liver, only one population of Kupffer cells was identified as F4/80(high)CD11b(low) cells. We observed that freshy isolated Kupffer cells are endocytic and show a relatively high basal ROS content. Interestingly, despite expression of TLR mRNA on Kupffer cells, ligation of TLR4, TLR7/8, and TLR9 resulted in a weak induction of IL-10, low or undetectable levels of IL-12p40 and TNF, and up-regulation of CD40 on the surface. Kupffer cells and splenic macrophages show functional similarities, in comparison with peritoneal macrophages, as reflected by comparable levels of TLR4, TLR7/8, and TLR9 mRNA and low or undetectable levels of TNF and IL-12p40 produced upon TLR ligation. The unique, functional characteristics of Kupffer cells, demonstrated in this study, suggest that Kupffer cells under steady-state conditions are specialized as phagocytes to clear and degrade particulates and only play a limited immunoregulatory role via the release of soluble mediators.

␤ 2 -Microglobulin (␤ 2 m) is a chaperone of major histocompatibility complex (MHC) class I (-like) molecules that play a central role in antigen presentation, immunoglobulin transport, and iron metabolism. It is therefore of importance that ␤ 2 m is adequately expressed in cells that perform these functions, such as hematopoietic cells. In this study, we investigated the transcriptional regulation of ␤ 2 m in lymphoid and myeloid cell lines through a promoter containing a putative E box, Ets/interferon-stimulated response element (ISRE), and B site. Here we show that upstream stimulatory factor 1 (USF1) and USF2 bind to the E box and regulate ␤ 2 m transactivation. The nuclear factor B (NF-B) subunits p50 and p65 bind to the B box and p65 transactivates ␤ 2 m. Interferon regulatory factor 1 (IRF1) , Introduction␤ 2 -Microglobulin (␤ 2 m) is a ubiquitously expressed 12-kDa glycoprotein that associates with major histocompatibility complex (MHC) class I (-like) molecules that are of great importance in antigen presentation, IgG transport, and iron metabolism. 1 As such, ␤ 2 m is linked to a variety of human diseases because of its association with immunologically and hematologically relevant molecules. ␤ 2 m is best known for its association with the MHC class I heavy chain, which is essential for the stable expression of these antigen-presenting molecules. Classical MHC class I molecules (HLA-A, -B, and -C) are ubiquitously expressed in most somatic cells. They are essential in the immune response because they present antigen-derived peptides to cytotoxic T lymphocytes and are important in protection against natural killer (NK) cellmediated cytotoxicity. 2 ␤ 2 m also associates with MHC class Ib or class I-like molecules, such as HLA-E, -F, -G, and CD1, which have a more restricted tissue distribution and have more specialized functions in antigen presentation. 3-5 ␤ 2 m is also a partner of HFE (formerly called HLA-H), an MHC class I-like molecule that is important for transferrin-mediated iron uptake. [6][7][8][9] Patients suffering from hereditary hemochromatosis have been found to bear a mutation in the HFE gene that specifically disrupts its association with ␤ 2 m, resulting in a strongly compromised function. 6,7 This is characterized by iron accumulation in parenchymal cells in various organs but a paucity of iron in Kupffer cells and macrophages. [6][7][8][9] Clinical consequences include liver cirrhosis, diabetes, arthritis, and heart failure. Furthermore, ␤ 2 m is also able to form a dimer with the neonatal Fc receptor, which is important for fetomaternal transport of IgG. 10,11 Finally, a role for ␤ 2 m has also been suggested in amyloidosis. Patients undergoing long-term dialysis often develop amyloidosis, which in turn affects bone cell metabolism by inducing bone mineral dissolving and enhancing osteoblast proliferation. 12,13 This is thought to be related to the binding of ␤ 2 m with ␣ 2 -macroglobulin and heparin sulfate. 14,15 Because ␤ 2 m is essential for the functioning of molecules central i...

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The class II transactivator (CIITA) plays a pivotal role in the expression of major histocompatibility complex (MHC) class II and accessory genes (invariant chain [Ii] and HLA-DM), whereas it has an ancillary function in the expression of MHC class I and ␤ 2 -microglobulin (␤ 2 m) genes. 1-9 The MHC is a large multigene family that encodes cell surface glycoproteins involved in binding and presentation of antigenic peptides to T lymphocytes. The products of the ␤ 2 m, Ii and HLA-DM genes are also essential proteins in MHC class I-and class II-mediated antigen presentation function, respectively. For this reason CIITA-mediated MHC expression is central in the generation of an antigen-specific immune response by presenting antigenic peptides to the T-cell receptor (TCR) on T lymphocytes. 10,11 MHC class I molecules are expressed on almost all nucleated cells. In contrast, the constitutive expression of MHC class II molecules is restricted to specific immune cell types that include antigen-presenting cells such as dendritic cells, B lymphocytes, macrophages and thymic epithelial cells. Nonimmune cells lack constitutive expression of MHC class II; however, in most of these cells MHC class II expression can be induced by interferon-␥ (IFN-␥). 12,13 Notably, expression of MHC class I molecules can also be enhanced by IFN-␥. Together, the upregulated expression of MHC class I and class II molecules results in an increase in the immunogenic potential of cells. The importance of MHC expression by tumor cells in mounting an effective antitumor immune response has been shown in animal models for T-cell-mediated immunotherapy 14 -16 and is corroborated by the notion that tumors expressing high levels of both MHC class I and class II molecules display abundant lymphocytic infiltration. [17][18][19] Notably, patients with high tumorlytic lymphocyte infiltrates generally have a better prognosis. [17][18][19] Several tissues have been shown to exhibit a significantly reduced membrane expression of MHC class I molecules. In particular, certain reproductive and developmental tissues lack expression of MHC class I molecules, including sperm, 20 oocytes, 21 preimplantation embryos 22 and villous trophoblast cells. 23 The absence of MHC molecules from fetal and embryonic tissues creates an immune privilege for these cells during gestation and may be of functional significance during development. Also, several malignant cell types have been shown to lack the expression of MHC molecules. This reduced expression of MHC molecules will contribute to a decreased recognition by T cells, allowing an escape from immunosurveillance. 24 -26 Interestingly, most of the MHC-deficient tumor cells have originated from fetal or embryonic tissues. Downregulation of MHC gene expression in these embryonic or developmental tumors may therefore not result from the neoplastic transformation event but may instead reflect the characteristic silent state of MHC class I and class II genes during early development.To understand the mechanisms of downregulat...