Dendritic cells: regulators of hepatic immunity or tolerance?

Comprehensive analysis of lncRNA-mediated ceRNA networkfor hepatocellular carcinoma

Background

Hepatocellular carcinoma (HCC) is a high-burden cancer. The molecular mechanism of HCC has not been fully elucidated. Notably, current research has revealed a significant function for long non-coding RNAs (lncRNAs) in the prognosis of patients with HCC. Here, this study aims to construct a regulated lncRNA-mediated ceRNA network and find biological targets for the treatment of HCC.

Methods

Based on the RNA expression patterns from the TCGA, we did an analysis to determine which genes were expressed differently between liver tumor tissues and noncancerous tissues. Then, using bioinformatic tools, we built a lncRNA-miRNA-mRNA ceRNA network and used GO and KEGG functional analyses on the DEmRNAs connected to ceRNA networks. The main lncRNAs in the subnetwork were chosen, and we next looked at the relationships between these lncRNAs and the clinical characteristics of patients with HCC. The prognosis-related genes and immune cells were identified using Kaplan-Meier and Cox proportional hazard analyses, and CIBERSORT was utilized to separate the 22 immune cell types. CCK8 assay was performed to measure cell viability in HCC cells after lncRNA HOTTIP modulation.

Results

Differentially expressed mRNA and lncRNAs in HCC and paracancerous tissues were identified. There are 245 lncRNAs, 126 miRNAs, and 1980 mRNAs that are expressed differently in liver tumour tissues than in noncancerous cells. Function analysis showed that mRNAs in ceRNA network were significantly enriched in G1/S transition of mototiv cell cycle, positive regulation of cell cycle process, hepatocellular carcinoma, and cancer related pathways. CD8 T cells and T follicular helper cells had a favourable link with a 0.65 correlation coefficient. Additionally, there was a strong correlation between Eosinophils, activated NK cells, and B memory cells. Strikingly, depletion of lncRNA HOTTIP inhibited viability of HCC cells. In addition, miR-205 upregulation suppressed viability of HCC cells, while miR-205 downregulation repressed viability of HCC cells. Notably, miR-205 depletion rescued HOTTIP depletion-mediated suppression of cell viability in HCC.

Conclusion

A ceRNA network was created by examining the lncRNA, miRNA, and mRNA expression profiles of liver tumours from the TCGA database. LncRNA HOTTIP promoted cell viability via inhibition of miR-205 in HCC cells.

Insights Into Human Intrahepatic NK Cell Function From Single Cell RNA Sequencing Datasets

Diverse populations of natural killer (NK) cells have been identified in circulating peripheral blood and a wide variety of different tissues and organs. These tissue-resident NK cell populations are phenotypically distinct from circulating NK cells, however, functional descriptions of their roles within tissues are lacking. Recent advances in single cell RNA sequencing (scRNA-seq) have enabled detailed transcriptional profiling of tissues at the level of single cells and provide the opportunity to explore NK cell diversity within tissues. This review explores potential novel functions of human liver-resident (lr)NK cells identified in human liver scRNA-seq studies. By comparing these datasets we identified up-regulated and down-regulated genes associated with lrNK cells clusters. These genes encode a number of activating and inhibiting receptors, as well as signal transduction molecules, which highlight potential unique pathways that lrNK cells utilize to respond to stimuli within the human liver. This unique receptor repertoire of lrNK cells may confer the ability to regulate a number of immune cell populations, such as circulating monocytes and T cells, while avoiding activation by liver hepatocytes and Kupffer cells. Validating the expression of these receptors on lrNK cells and the proposed cellular interactions within the human liver will expand our understanding of the liver-specific homeostatic roles of this tissue-resident immune cell population.

Immunomodulatory effects of transforming growth factor-β in the liver

Members of the transforming growth factor-β (TGF-β) family are potent regulatory cytokines that affect multiple cell types of the immune system mediating pro-inflammatory or anti-inflammatory responses. In the liver, TGF-β is produced by a multitude of non-parenchymal liver cells including hepatic stellate cells (HSCs), liver sinusoidal endothelial cells (LSECs), Kupffer cells (KCs), and dendritic cells (DCs) as well as natural killer (NK) T cells among other hepatic lymphocytes. The effect of TGF-β on other cells is highly versatile. In concert with other soluble factors, it controls the maturation, differentiation and activity of various T cell subsets that either prevent or actuate infections, graft-versus-host reactions, immune diseases, and cancer formation. During the last decades, it became evident that some TGFB1 polymorphisms are associated with the pathogenesis of hepatic disease and that plasma TGF-β is a suitable biomarker to detect liver lesions. Moreover, since TGF-β has capacity to influence the quantity and quality of T cell subsets as well as their activity, it is obvious that a well-balanced TGF-β activity is essential for liver homeostasis. In the present review, we highlight some pivotal functions of TGF-β in hepatic immunobiology. We discuss its regulatory function on adaptive immunity, the impact on differentiation of various T cell subsets, its crosstalk with Toll like receptor signaling, and its contribution to functional impairment of the liver.

Cellular immune response against firefly luciferase after sleeping beauty-mediated gene transfer in vivo

The Sleeping Beauty (SB) transposon system has been shown to mediate new gene sequence integration resulting in long-term expression. Here the effectiveness of hyperactive SB100X transposase was tested, and we found that hydrodynamic co-delivery of a firefly luciferase transposon (pT2/CaL) along with SB100X transposase (pCMV-SB100X) resulted in remarkably sustained, high levels of luciferase expression. However, after 4 weeks there was a rapid, animal-by-animal loss of luciferase expression that was not observed in immunodeficient mice. We hypothesized that this sustained, high-level luciferase expression achieved using the SB100X transposase elicits an immune response in pT2/CaL co-administered mice, which was supported by the rapid loss of luciferase expression upon challenge of previously treated animals and in naive animals adoptively transferred with splenocytes from previously treated animals. Specificity of the immune response to luciferase was demonstrated by increased cytokine expression in splenocytes after exposure to luciferase peptide in parallel with MHC I-luciferase peptide tetramer binding. This anti-luciferase immune response observed following continuous, high-level luciferase expression in vivo clearly impacts its use as an in vivo reporter. As both an immunogen and an extremely sensitive reporter, luciferase is also a useful model system for the study of immune responses following in vivo gene transfer and expression.

Microanatomy of the liver immune system

The critical metabolic functions of the liver often eclipse any perception of its role as an immune organ. However, the liver as a mediator of systemic and local innate immunity and an important site of immune regulation is now an accepted concept. Complex repertoires of lymphoid and non-lymphoid cells are key to hepatic defense and immunoregulation. Hepatic cells of myeloid lineage include Kupffer cells and dendritic cells. Intrahepatic lymphocytes are distinct both in phenotype and function from their counterparts in any other organ and include both conventional (CD4+ and CD8+ alphabeta T cell receptor (TCR)+ T cells, B cells, natural killer (NK) cells) and nonconventional lymphoid cells (natural killer T (NKT) cells, gamma delta TCR+ T cells, CD4- CD8- T cells). Many hepatic T cells express the TCR at an intermediate level and the great majority of them either coexpress NK cell markers (NKT cells) or they are apoptosing peripheral T cells. The percentage of activated (CD69+) and memory (CD45RB low+) lymphocytes is much higher while naive (CD62L high) and resting T cells as well as B lymphocytes are underrepresented in the liver. The discovery of major populations of lymphoid cells in the liver that differ phenotypically, functionally and even perhaps developmentally from populations in other regions has been key to the evolving perception of the liver as a regulatory lymphoid organ. This chapter will focus on these populations and how they contribute to immune surveillance against malignant, infectious and autoimmune disease of the liver.

Hepatic microenvironment programs hematopoietic progenitor differentiation into regulatory dendritic cells, maintaining liver tolerance

The liver has been generally considered an organ prone to tolerance induction and maintenance. However, whether and how the unique liver microenvironment contributes to tolerance maintenance is largely unknown. Here, we used liver fibroblastic stromal cells to mimic the liver microenvironment and found that liver stroma could induce Lin(-)CD117(+) progenitors to differentiate into dendritic cells (DCs) with low CD11c, MHC II but high CD11b expression, high IL-10, but low IL-12 secretion. Such regulatory DCs could inhibit T-cell proliferation in vitro and in vivo, induce apoptosis of the activated T cells, and alleviate the damage of autoimmune hepatitis. Furthermore, liver stroma-derived macrophage colony-stimulating factor (M-CSF) was found to contribute to the generation of such regulatory DCs. Regulatory DC-derived PGE2 and T cell-derived IFN-gamma were responsible for the regulatory function. The natural counterpart of regulatory DCs was phenotypically and functionally identified in the liver. Importantly, Lin(-)CD117(+) progenitors could be differentiated into regulatory DCs in the liver once transferred into the liver. Infusion with liver regulatory DCs alleviated experimental autoimmune hepatitis. Therefore, we demonstrate that the liver microenvironment is highly important to program progenitors to differentiate into regulatory DCs in situ, which contributes to the maintenance of liver tolerance.

NK cell-like behavior of Valpha14i NK T cells during MCMV infection

Immunity to the murine cytomegalovirus (MCMV) is critically dependent on the innate response for initial containment of viral replication, resolution of active infection, and proper induction of the adaptive phase of the anti-viral response. In contrast to NK cells, the Valpha14 invariant natural killer T cell response to MCMV has not been examined. We found that Valpha14i NK T cells become activated and produce significant levels of IFN-gamma, but do not proliferate or produce IL-4 following MCMV infection. In vivo treatment with an anti-CD1d mAb and adoptive transfer of Valpha14i NK T cells into MCMV-infected CD1d(-/-) mice demonstrate that CD1d is dispensable for Valpha14i NK T cell activation. In contrast, both IFN-alpha/beta and IL-12 are required for optimal activation. Valpha14i NK T cell-derived IFN-gamma is partially dependent on IFN-alpha/beta but highly dependent on IL-12. Valpha14i NK T cells contribute to the immune response to MCMV and amplify NK cell-derived IFN-gamma. Importantly, mortality is increased in CD1d(-/-) mice in response to high dose MCMV infection when compared to heterozygote littermate controls. Collectively, these findings illustrate the plasticity of Valpha14i NK T cells that act as effector T cells during bacterial infection, but have NK cell-like behavior during the innate immune response to MCMV infection.

Decrease and dysfunction of dendritic cells correlate with impaired hepatitis C virus-specific CD4+ T-cell proliferation in patients with hepatitis C virus infection

Through the production of stimulatory and suppressive cytokines, dendritic cells (DCs) regulate virus-specific immune responses that are crucial to virus eradication. To explore a possible role of DCs in the persistence of hepatitis C virus (HCV) infection, in this study we analysed peripheral blood DCs (PBDCs) in patients with chronic hepatitis C (CHC) compared with those in both healthy seronegative (HSN) controls and a group of subjects who had spontaneously resolved infection, defined as healthy HCV-seropositive (HSP), and we evaluated the relationships between PBDCs and HCV-specific CD4(+) T-cell reactivity. The number of PBDCs, their immunophenotype and expression of regulatory cytokines were evaluated by flow cytometry on whole-blood samples. HCV-specific CD4(+) T-cell activation, proliferation and cytokine production were evaluated in cultures of peripheral blood mononuclear cells (PBMCs) stimulated in vitro with HCV peptides. We found that PBDCs from CHC subjects were numerically reduced and showed lower interleukin-12 (IL-12) and higher IL-10 expression than those from HSN controls. PBDCs from HSP subjects were similar to those from HSN controls. HCV-specific CD4(+) T-cell proliferation was less frequent and vigorous in CHC than in HSP patients and was directly related to the number of PBDCs and their IL-12 production but inversely related to their IL-10 production. Taken together, these results seem to suggest that cytokines of DC origin contribute to the regulation of HCV-specific immunity in CHC patients and indicate that PBDCs may represent a novel non-invasive tool for immune monitoring of these patients.

Nomadic or sessile: can Kupffer cells function as portals for malaria sporozoites to the liver?

The initial site of replication for Plasmodium parasites in mammalian hosts are hepatocytes, cells that offer unique advantages for the extensive parasite replication occurring prior to the erythrocytic phase of the life cycle. The liver is the metabolic centre of the body and has an unusual relationship to the immune system. However, to reach hepatocytes, sporozoites must cross the sinusoidal barrier, composed of specialized endothelia and Kupffer cells, the resident macrophages of the liver. Mounting evidence suggests that, instead of taking what would seem a safer route through endothelia, the parasites traverse Kupffer cells yet suffer no harm. Kupffer cells have a broad range of responses towards incoming microorganisms, toxins and antigens which depend on the nature of the intruder, the experimental conditions and the environmental circumstances. Kupffer cells may become activated or remain anergic, produce pro- or anti-inflammatory mediators. Consequently, outcomes are diverse and include development of immunity or tolerance, parenchymal necrosis or regeneration, chronic cirrhotic transformation or acute liver failure. Here we review data concerning the unique structural and functional characteristics of Kupffer cells and their interactions with Plasmodium sporozoites in the context of a model in which these hepatic macrophages function as the sporozoite gate to the liver.

Hepatic environment elicits monocyte differentiation into a dendritic cell subset directing Th2 response

BACKGROUND/AIMS

Dendritic cells (DCs), which play a critical role during immune response, could present alternative differentiation patterns depending on tissue microenvironment. Our aim was to examine the influence of hepatic microenvironment on human monocyte differentiation into DCs.

METHODS

Cytology, immunophenotyping, cytokine production and T-cell activation were analyzed in DCs differentiated from human monocytes co-cultured with rat liver epithelial cells (RLEC) or human cells from various tissue origins and compared to control DCs obtained on plastic with GM-CSF/IL-4.

RESULTS

RLEC environment promotes DC differentiation in the presence of IL-4 without GM-CSF. These DCs evidence similar expression of MHC-II, co-stimulatory and adhesion molecules than control DCs, but distinct lineage markers defining a CD11c+/CD14+/CD123+ DC subset. This phenotype is common to DCs from RLEC and human liver environment and differs from that obtained with skin or intestine environments. Functionally, they produce IL-10 but not IL-12p70 and favor IL-4/IL-10 secretion by T-cells rather than IFN-gamma.

CONCLUSIONS

Our results confirm that tissue niches modulate DC differentiation and demonstrate that hepatic environment influences monocyte differentiation into a DC subset directing Th2 response, a key data for understanding the specialized immune response in liver. They also make RLEC co-culture system useful for studying liver DC functions.

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Sneaking in through the back entrance: the biology of malaria liver stages

Malaria infection is caused by sporozoites, the life cycle stage of Plasmodium that is transmitted by female anopheline mosquitoes. The inoculated sporozoites migrate in the skin, enter a capillary and use the bloodstream for the long haul to the liver. Here, the parasites invade hepatocytes and differentiate to thousands of merozoites that specifically infect red blood cells. Hepatocytes, however, are not directly accessible to sporozoites entering the liver sinusoid. The liver phase of the malaria life cycle can occur only if the parasites first cross the layer of sinusoidal cells that line the liver capillaries. Experimental observations show that sporozoite entry into the liver parenchyma involves a complex cascade of events, from binding to extracellular matrix proteoglycans via passage through Kupffer cells and transmigration through several hepatocytes, until the final host cell is found. By choosing the liver as their initial site of replication, Plasmodium sporozoites can exploit the tolerogenic properties of this unique immune organ to evade the host's immune response.

Defective antigen-presenting capacity of murine dendritic cells during starvation

Significant impairments of several aspects of immunity have been described in acute and chronic nutritional deficiencies; however, there have been few studies on antigen-presenting cells during starvation. We examined the antigen-presenting capacities of mouse dendritic cells (DCs) from lymphoid organ (spleen DCs) and non-lymphoid tissue (liver DCs) during starvation. The total numbers of spleen DCs and liver DCs were significantly fewer in starved mice than in control mice. Functional analysis showed that the proliferative activities of spleen DCs and liver DCs were significantly impaired in starved mice compared with control mice. In particular, liver DCs from starved mice were unable to induce interferon-gamma. Liver DCs from starved mice were unable to induce proliferation of antigen-specific memory lymphocytes. These data indicated that one major cause of impairment of immunologic responses during starvation may be mediated through DCs.

Hepatobiliary pathology

Technologic advances using cDNA microarray hybridization, liver diseases characterized by mitochondrial DNA depletion, and new work characterizing bile salt transport problems in familial intrahepatic cholestasis syndromes were some of the major highlights of this past year. Analysis of normal livers by cDNA microarrays disclosed 2418 unique gene transcripts encoding a host of cellular structural and functional proteins. This technique was also applied to hepatocellular carcinoma, where enhanced expression of a number of genes involved in antiapoptosis and cell transformation may shed additional light on the process of hepatocarcinogenesis. Mitochondrial DNA depletion seen in Navajo neurohepatopathy and in respiratory chain disorders of infancy was associated with cholestasis and cirrhosis in the former and microvesicular steatosis and oncocytic transformation (mitochondrial hyperplasia) in the latter. Pathologists who routinely examine liver biopsies after liver or bone marrow transplantation should be aware of unusual biopsy features that mimic other diseases, such as the autoimmune hepatitis-like syndrome that may follow liver transplantation and chronic graft-versus-host disease that clinically and pathologically resembles acute hepatitis.

Role of primary intrahepatic T-cell activation in the 'liver tolerance effect'

There is accumulating evidence suggesting that hepatic permeability to both naive and activated T lymphocytes may be unique among the solid organs. The possibility that the liver may act as a site of primary activation for CD8+ T lymphocytes is supported by experimental data and may contribute to some of the unique immunological properties of this organ, particularly its ability to induce antigen-specific tolerance. This review discusses the nature of the liver APC inducing primary T-cell activation within the liver: Kupffer cells, liver dendritic cells, liver sinusoidal endothelial cells and hepatocytes are favourably located to allow physical contact with circulating T lymphocytes. Here, we examine the capability of each cell type to act as APC for naive CD4+ or CD8+ T cells and to induce tolerance.