Restoration of TLR3-activated myeloid dendritic cell activity leads to improved natural killer cell function in chronic hepatitis B virus infection

There is increasing evidence that the function of NK cells in patients with chronic hepatitis B (CHB) infection is impaired. The underlying mechanism for the impaired NK cell function is still unknown. Since myeloid dendritic cells (mDC) are potent inducers of NK cells, we investigated the functional interaction of mDC and NK cells in CHB and the influence of antiviral therapy. Blood BDCA1+ mDC and NK cells were isolated from 16 healthy controls or 39 CHB patients at baseline and during 6 months of antiviral therapy. After activation of mDC with poly(I C) and gamma interferon (IFN-γ), mDC were cocultured with NK cells. Phenotype and function were analyzed in detail by flow cytometry and enzyme-linked immunosorbent assay. Our findings demonstrate that on poly(I C)/IFN-γ-stimulated mDC from CHB patients, the expression of costimulatory molecules was enhanced, while cytokine production was reduced. In cocultures of poly(I C)/IFN-γ-stimulated mDC and NK cells obtained from CHB patients, reduced mDC-induced NK cell activation (i.e., CD69 expression) and IFN-γ production compared to those in healthy individuals was observed. Antiviral therapy normalized mDC activity, since decreased expression of CD80 and CD86 on DC and of HLA-E on NK cells was observed, while poly(I C)/IFN-γ-induced cytokine production by mDC was enhanced. In parallel, successful antiviral therapy resulted in improved mDC-induced NK cell activation and IFN-γ production. These data demonstrate that CHB patients display a diminished functional interaction between poly(I C)/IFN-γ activated mDC and NK cells due to impaired mDC function, which can be partially restored by antiviral therapy. Enhancing this reciprocal interaction could reinforce the innate and thus the adaptive T cell response, and this may be an important step in achieving effective antiviral immunity

Kupffer cells express a unique combination of phenotypic and functional characteristics compared with splenic and peritoneal macrophages

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/ 80highCD11blow 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

The DNA-binding factor Ctcf critically controls gene expression in macrophages

Macrophages play an important role in immunity and homeostasis. Upon pathogen recognition via specific receptors, they rapidly induce inflammatory responses. This process is tightly controlled at the transcriptional level. The DNA binding zinc-finger protein CCCTC-binding factor (Ctcf) is a crucial regulator of long-range chromatin interactions and coordinates specific communication between transcription factors and gene expression processes. In this study, the Ctcf gene was specifically deleted in myeloid cells by making use of the transgenic Cre-LoxP system. Conditional deletion of the Ctcf gene in myeloid cells induced a mild phenotype in vivo. Ctcf-deficient mice exhibited significantly reduced expression of major histocompatibility complex (MHC) class II in the liver. Ctcf-deficient macrophages demonstrated a normal surface phenotype and phagocytosis capacity. Upon Toll-like receptor (TLR) stimulation, they produced normal levels of the pro-inflammatory cytokines IL-12 and IL-6, but manifested a strongly impaired capacity to produce tumor-necrosis factor (TNF) and IL-10, as well as to express the IL-10 family members IL-19, IL-20 and IL-24. Taken together, our data demonstrate a role of Ctcf that involves fine-tuning of macrophage function

Inflammatory monocytes recruited to the liver within 24 hours after virus-induced inflammation resemble kupffer cells but are functionally distinct

Due to a scarcity of immunocompetent animal models for viral hepatitis, little is known about the early innate immune responses in the liver. In various hepatotoxic models, both pro- and anti-inflammatory activities of recruited monocytes have been described. In this study, we compared the effect of liver inflammation induced by the Toll-like receptor 4 ligand lipopolysaccharide (LPS) with that of a persistent virus, lymphocytic choriomeningitis virus (LCMV) clone 13, on early innate intrahepatic immune responses in mice. LCMV infection induces a remarkable influx of inflammatory monocytes in the liver within 24 h, accompanied by increased transcript levels of several proinflammatory cytokines and chemokines in whole liver. Importantly, while a single LPS injection results in similar recruitment of inflammatory monocytes to the liver, the functional properties of the infiltrating cells are dramatically different in response to LPS versus LCMV infection. In fact, intrahepatic inflammatory monocytes are skewed toward a secretory phenotype with impaired phagocytosis in LCMV-induced liver inflammation but exhibit increased endocytic capacity after LPS challenge. In contrast, F4/80high-Kupffer cells retain their steady-state endocytic functions upon LCMV infection. Strikingly, the gene expression levels of inflammatory monocytes dramatically change upon LCMV exposure and resemble those of Kupffer cells. Since inflammatory monocytes outnumber Kupffer cells 24 h after LCMV infection, it is highly likely that inflammatory monocytes contribute to the intrahepatic inflammatory response during the early phase of infection. Our findings are instrumental in understanding the early immunological events during virus-induced liver disease and point toward inflammatory monocytes as potential target cells for future treatment options in viral hepatitis