Liver-resident CD103+ dendritic cells prime antiviral CD8+ T cells in situ

Active role of the immune system in metabolic dysfunction-associated steatotic liver disease

Non-alcoholic fatty liver disease, recently renamed metabolic dysfunction-associated steatotic liver disease (MASLD), is a complex multifactorial disease that progresses from steatohepatitis (MASH) to liver cirrhosis and liver cancer. Recent research has revealed that crosstalk between innate immune cells and hepatic parenchymal and non-parenchymal cells is involved in the pathogenesis of liver disease in MASLD/MASH. Of particular importance, novel inflammatory mechanisms, including macrophage diversity, neutrophil NETosis, B-cell biology, auto-reactive T cells, unconventional T cells, and dendritic cell-T cell interactions, are considered key drivers for disease progression. These mechanisms and factors are potential targets for the therapeutic intervention of MASLD/MASH. In this review, we focus on recent discoveries related to liver inflammation and discuss the role of innate immune cell subsets in MASLD/MASH.

Conventional type 1 dendritic cells are essential for the development of primary biliary cholangitis

BACKGROUND & AIMS

Primary biliary cholangitis (PBC) is a progressive-cholestatic autoimmune liver disease. Dendritic cells (DC) are professional antigen-presenting cells and their prominent presence around damaged bile ducts of PBC patients are documented. cDC1 is a rare subset of DC known for its cross-presentation abilities and interleukin 12 production. Our aim was to assess the role of cDC1 in the pathogenesis of PBC.

METHODS

We utilized an inducible murine model of PBC and took advantage of the DC reporter mice Zbtb46gfp and the Batf3-/- mice that specifically lack the cDC1 subset. cDC1 cells were sorted from blood of PBC patients and healthy individuals and subjected to Bulk-MARS-seq transcriptome analysis.

RESULTS

Histopathology assessment demonstrated peri-portal inflammation in wild type (WT) mice, whereas only minor abnormalities were observed in Batf3-/- mice. Flow cytometry analysis revealed a two-fold reduction in hepatic CD8/CD4 T cells ratio in Batf3-/- mice, suggesting reduced intrahepatic CD8 T cells expansion. Histological evidence of portal fibrosis was detected only in the WT but not in Batf3-/- mice. This finding was supported by decreased expression levels of pro-fibrotic genes in the livers of Batf3-/- mice. Transcriptome analysis of human cDC1, revealed 78 differentially expressed genes between PBC patients and controls. Genes related to antigen presentation, TNF and IFN signalling and mitochondrial dysfunction were significantly increased in cDC1 isolated from PBC patients.

CONCLUSION

Our data illustrated the contribution the cDC1 subset in the pathogenesis of PBC and provides a novel direction for immune based cell-specific targeted therapeutic approach in PBC.

TLR9-independent CD8+ T cell responses in hepatic AAV gene transfer through IL-1R1-MyD88 signaling

Upon viral infection of the liver, CD8+ T cell responses may be triggered despite the immune suppressive properties that manifest in this organ. We sought to identify pathways that activate responses to a neoantigen expressed in hepatocytes, using adeno-associated viral (AAV) gene transfer. It was previously established that cooperation between plasmacytoid dendritic cells (pDCs), which sense AAV genomes by Toll-like receptor 9 (TLR9), and conventional DCs promotes cross-priming of capsid-specific CD8+ T cells. Surprisingly, we find local initiation of a CD8+ T cell response against antigen expressed in ∼20% of murine hepatocytes, independent of TLR9 or type I interferons and instead relying on IL-1 receptor 1-MyD88 signaling. Both IL-1α and IL-1β contribute to this response, which can be blunted by IL-1 blockade. Upon AAV administration, IL-1-producing pDCs infiltrate the liver and co-cluster with XCR1+ DCs, CD8+ T cells, and Kupffer cells. Analogous events were observed following coagulation factor VIII gene transfer in hemophilia A mice. Therefore, pDCs have alternative means of promoting anti-viral T cell responses and participate in intrahepatic immune cell networks similar to those that form in lymphoid organs. Combined TLR9 and IL-1 blockade may broadly prevent CD8+ T responses against AAV capsid and transgene product.

Immune Responses Induced at One Hour Post Cataract Surgery Wounding of the Chick Lens

While the lens is an avascular tissue with an immune-privileged status, studies have now revealed that there are immune responses specifically linked to the lens. The response to lens injury, such as following cataract surgery, has been shown to involve the activation of the resident immune cell population of the lens and the induction of immunomodulatory factors by the wounded epithelium. However, there has been limited investigation into the immediate response of the lens to wounding, particularly those induced factors that are intrinsic to the lens and its associated resident immune cells. Using an established chick embryo ex vivo cataract surgery model has made it possible to determine the early immune responses of this tissue to injury, including its resident immune cells, through a transcriptome analysis. RNA-seq studies were performed to determine the gene expression profile at 1 h post wounding compared to time 0. The results provided evidence that, as occurs in other tissues, the resident immune cells of the lens rapidly acquired a molecular signature consistent with their activation. These studies also identified the expression of many inflammatory factors by the injured lens that are associated with both the induction and regulation of the immune response.

The liver contains distinct interconnected networks of CX3CR1 + macrophages, XCR1 + type 1 and CD301a + type 2 conventional dendritic cells embedded within portal tracts

Portal tracts are key intrahepatic structures where leukocytes accumulate during immune responses. They contain the blood inflow, which includes portal blood from the gut, and lymphatic and biliary outflow of the liver, and as such represent a key interface for potential pathogen entry to the liver. Myeloid cells residing in the interstitium of the portal tract might play an important role in the surveillance or prevention of pathogen dissemination; however, the exact composition and localization of this population has not been explored fully. Our in‐depth characterization of portal tract myeloid cells revealed that in addition to T lymphocytes, portal tracts contain a heterogeneous population of MHCII^high myeloid cells with potential antigen presenting cell (APC) function. These include a previously unreported subset of CSF1R‐dependent CX3CR1⁺ macrophages that phenotypically and morphologically resemble liver capsular macrophages, as well as the two main dendritic cell subsets (cDC1 and cDC2). These cells are not randomly distributed, but each subset forms interconnected networks intertwined with specific components of the portal tract. The CX3CR1⁺ cells were preferentially detected along the outer border of the portal tracts, and also in the portal interstitium adjacent to the portal vein, bile duct, lymphatic vessels and hepatic artery. cDC1s abounded along the lymphatic vessels, while cDC2s mostly surrounded the biliary tree. The specific distributions of these discrete subsets predict that they may serve distinct functions in this compartment. Overall, our findings suggest that portal tracts and their embedded cellular networks of myeloid cells form a distinctive lymphoid compartment in the liver that has the potential to orchestrate immune responses in this organ.

The Emerging Role of Tissue-Resident Memory CD8+ T Lymphocytes in Human Digestive Tract Cancers

Malignant digestive tract tumors are a great threat to human public health. In addition to surgery, immunotherapy brings hope for the treatment of these tumors. Tissue-resident memory CD8⁺ T (Trm) cells are a focus of tumor immunology research and treatment due to their powerful cytotoxic effects, ability to directly kill epithelial-derived tumor cells, and overall impact on maintaining mucosal homeostasis and antitumor function in the digestive tract. They are a group of noncirculating immune cells expressing adhesion and migration molecules such as CD69, CD103, and CD49a that primarily reside on the barrier epithelium of nonlymphoid organs and respond rapidly to both viral and bacterial infection and tumorigenesis. This review highlights new research exploring the role of CD8⁺ Trm cells in a variety of digestive tract malignant tumors, including esophageal cancer, gastric cancer, colorectal cancer, and hepatocellular carcinoma. A summary of CD8⁺ Trm cell phenotypes and characteristics, tissue distribution, and antitumor functions in different tumor environments is provided, illustrating how these cells may be used in immunotherapies against digestive tract tumors.

Identification of Two Subsets of Murine DC1 Dendritic Cells That Differ by Surface Phenotype, Gene Expression, and Function

Classical dendritic cells (cDCs) in mice have been divided into 2 major subsets based on the expression of nuclear transcription factors: a CD8⁺Irf8⁺Batf3 dependent (DC1) subset, and a CD8^-Irf4⁺ (DC2) subset. We found that the CD8⁺DC1 subset can be further divided into CD8⁺DC1a and CD8⁺DC1b subsets by differences in surface receptors, gene expression, and function. Whereas all 3 DC subsets can act alone to induce potent Th1 cytokine responses to class I and II MHC restricted peptides derived from ovalbumin (OVA) by OT-I and OT-II transgenic T cells, only the DC1b subset could effectively present glycolipid antigens to natural killer T (NKT) cells. Vaccination with OVA protein pulsed DC1b and DC2 cells were more effective in reducing the growth of the B16-OVA melanoma as compared to pulsed DC1a cells in wild type mice. In conclusion, the Batf3-/- dependent DC1 cells can be further divided into two subsets with different immune functional profiles in vitro and in vivo.

The immunological and metabolic landscape in primary and metastatic liver cancer

The liver is the sixth most common site of primary cancer in humans, and generally arises in a background of cirrhosis and inflammation. Moreover, the liver is frequently colonized by metastases from cancers of other organs (particularly the colon) because of its anatomical location and organization, as well as its unique metabolic and immunosuppressive environment. In this Review, we discuss how the hepatic microenvironment adapts to pathologies characterized by chronic inflammation and metabolic alterations. We illustrate how these immunological or metabolic changes alter immunosurveillance and thus hinder or promote the development of primary liver cancer. In addition, we describe how inflammatory and metabolic niches affect the spreading of cancer metastases into or within the liver. Finally, we review the current therapeutic options in this context and the resulting challenges that must be surmounted.

The Liver and the Hepatic Immune Response in Trypanosoma cruzi Infection, a Historical and Updated View

Chagas disease was described more than a century ago and, despite great efforts to understand the underlying mechanisms that lead to cardiac and digestive manifestations in chronic patients, much remains to be clarified. The disease is found beyond Latin America, including Japan, the USA, France, Spain, and Australia, and is caused by the protozoan Trypanosoma cruzi. Dr. Carlos Chagas described Chagas disease in 1909 in Brazil, and hepatomegaly was among the clinical signs observed. Currently, hepatomegaly is cited in most papers published which either study acutely infected patients or experimental models, and we know that the parasite can infect multiple cell types in the liver, especially Kupffer cells and dendritic cells. Moreover, liver damage is more pronounced in cases of oral infection, which is mainly found in the Amazon region. However, the importance of liver involvement, including the hepatic immune response, in disease progression does not receive much attention. In this review, we present the very first paper published approaching the liver's participation in the infection, as well as subsequent papers published in the last century, up to and including our recently published results. We propose that, after infection, activated peripheral T lymphocytes reach the liver and induce a shift to a pro-inflammatory ambient environment. Thus, there is an immunological integration and cooperation between peripheral and hepatic immunity, contributing to disease control.

Hepatic Dendritic Cells in the Development and Progression of Metabolic Steatohepatitis

Metabolic Associated Fatty liver disease (MAFLD) is a global health problem and represents the most common cause of chronic liver disease in the world. MAFLD spectrum goes from simple steatosis to cirrhosis, in between metabolic steatohepatitis with progressive fibrosis, which pathogenesis is not completely understood. Hence, the role of the immune system has become an important fact in the trigger of inflammatory cascades in metabolic steatohepatitis and in the activation of hepatic stellate cells (HSCs). Among, the more studied immune cells in the pathogenesis of MAFLD are macrophages, T cells, natural killer and dendritic cells. In particular, hepatic dendritic cells had recently attracted a special attention, with a dual role in the pathogenesis of MAFLD. These cells have the capacity to switch from a tolerant state to active state inducing an inflammatory cascade. Furthermore, these cells play a role in the lipid storage within the liver, having, thus providing a crucial nexus between inflammation and lipid metabolism. In this review, we will discuss the current knowledge on the dual role of dendritic cells in lipid accumulation, as wells as in the triggering of hepatic inflammation and hepatocytes cell death in metabolic steatohepatitis.

Understanding, predicting and achieving liver transplant tolerance: from bench to bedside

In the past 40 years, liver transplantation has evolved from a high-risk procedure to one that offers high success rates for reversal of liver dysfunction and excellent patient and graft survival. The liver is the most tolerogenic of transplanted organs; indeed, immunosuppressive therapy can be completely withdrawn without rejection of the graft in carefully selected, stable long-term liver recipients. However, in other recipients, chronic allograft injury, late graft failure and the adverse effects of anti-rejection therapy remain important obstacles to improved success. The liver has a unique composition of parenchymal and immune cells that regulate innate and adaptive immunity and that can promote antigen-specific tolerance. Although the mechanisms underlying liver transplant tolerance are not well understood, important insights have been gained into how the local microenvironment, hepatic immune cells and specific molecular pathways can promote donor-specific tolerance. These insights provide a basis for the identification of potential clinical biomarkers that might correlate with tolerance or rejection and for the development of novel therapeutic targets. Innovative approaches aimed at promoting immunosuppressive drug minimization or withdrawal include the adoptive transfer of donor-derived or recipient-derived regulatory immune cells to promote liver transplant tolerance. In this Review, we summarize and discuss these developments and their implications for liver transplantation.

Impact of anatomic site on antigen-presenting cells in cancer

Checkpoint blockade immunotherapy (CBT) can induce long-term clinical benefits in patients with advanced cancer; however, response rates to CBT vary by cancer type. Cancers of the skin, lung, and kidney are largely responsive to CBT, while cancers of the pancreas, ovary, breast, and metastatic lesions to the liver respond poorly. The impact of tissue-resident immune cells on antitumor immunity is an emerging area of investigation. Recent evidence indicates that antitumor immune responses and efficacy of CBT depend on the tissue site of the tumor lesion. As myeloid cells are predominantly tissue-resident and can shape tumor-reactive T cell responses, it is conceivable that tissue-specific differences in their function underlie the tissue-site-dependent variability in CBT responses. Understanding the roles of tissue-specific myeloid cells in antitumor immunity can open new avenues for treatment design. In this review, we discuss the roles of tissue-specific antigen-presenting cells (APCs) in governing antitumor immune responses, with a particular focus on the contributions of tissue-specific dendritic cells. Using the framework of the Cancer-Immunity Cycle, we examine the contributions of tissue-specific APC in CBT-sensitive and CBT-resistant carcinomas, highlight how these cells can be therapeutically modulated, and identify gaps in knowledge that remain to be addressed.

The Role of Dendritic Cells During Infections Caused by Highly Prevalent Viruses

Dendritic cells (DCs) are a type of innate immune cells with major relevance in the establishment of an adaptive response, as they are responsible for the activation of lymphocytes. Since their discovery, several reports of their role during infectious diseases have been performed, highlighting their functions and their mechanisms of action. DCs can be categorized into different subsets, and each of these subsets expresses a wide arrange of receptors and molecules that aid them in the clearance of invading pathogens. Interferon (IFN) is a cytokine -a molecule of protein origin- strongly associated with antiviral immune responses. This cytokine is secreted by different cell types and is fundamental in the modulation of both innate and adaptive immune responses against viral infections. Particularly, DCs are one of the most important immune cells that produce IFN, with type I IFNs (α and β) highlighting as the most important, as they are associated with viral clearance. Type I IFN secretion can be induced via different pathways, activated by various components of the virus, such as surface proteins or genetic material. These molecules can trigger the activation of the IFN pathway trough surface receptors, including IFNAR, TLR4, or some intracellular receptors, such as TLR7, TLR9, and TLR3. Here, we discuss various types of dendritic cells found in humans and mice; their contribution to the activation of the antiviral response triggered by the secretion of IFN, through different routes of the induction for this important antiviral cytokine; and as to how DCs are involved in human infections that are considered highly frequent nowadays.

Tissue-Resident NK Cells: Development, Maturation, and Clinical Relevance

Natural killer (NK) cells belong to type 1 innate lymphoid cells (ILC1) and are essential in killing infected or transformed cells. NK cells mediate their effector functions using non-clonotypic germ-line-encoded activation receptors. The utilization of non-polymorphic and conserved activating receptors promoted the conceptual dogma that NK cells are homogeneous with limited but focused immune functions. However, emerging studies reveal that NK cells are highly heterogeneous with divergent immune functions. A distinct combination of several activation and inhibitory receptors form a diverse array of NK cell subsets in both humans and mice. Importantly, one of the central factors that determine NK cell heterogeneity and their divergent functions is their tissue residency. Decades of studies provided strong support that NK cells develop in the bone marrow. However, evolving evidence supports the notion that NK cells also develop and differentiate in tissues. Here, we summarize the molecular basis, phenotypic signatures, and functions of tissue-resident NK cells and compare them with conventional NK cells.

Host CD8α+ and CD103+ dendritic cells prime transplant antigen-specific CD8+ T cells via cross-dressing

The participation of dendritic cells (DCs) in CD8⁺ T-cell-mediated allograft rejection is a long-standing question of great clinical relevance for tissue transplantation. Here, we show that Batf3^-/- mice demonstrate delayed allo-skin graft rejection and are deficient in priming allo-specific CD8⁺ T cells. Batf3^-/- mouse priming is restored by transferring either purified CD8α⁺ or CD103⁺ DCs, demonstrating the critical role of these cells in alloreactivity. Using D^b -restricted antiviral F5 transgenic T-cell receptor T cells, which we demonstrate are alloreactive with H-2K^d , we show that cross-dressing of CD8α⁺ and CD103⁺ primes CD8⁺ T-cell or allo-specific responses in vitro and in vivo. These findings suggest novel strategies for moderating tissue rejection based on interfering with DC cross-dressing or subsequent interaction with T cells.

Flt3 inhibition alleviates chronic kidney disease by suppressing CD103+ dendritic cell-mediated T cell activation

BACKGROUND

Chronic kidney disease (CKD) is a global public health problem, which lacks effective treatment. Previously, we have shown that CD103+ dendritic cells (DCs) are pathogenic in adriamycin nephropathy (AN), a model of human focal segmental glomerulosclerosis (FSGS). Fms-like tyrosine kinase 3 (Flt3) is a receptor that is expressed with high specificity on tissue resident CD103+ DCs.

METHODS

To test the effect on CD103+ DCs and kidney injury of inhibition of Flt3, we used a selective Flt3 inhibitor (AC220) to treat mice with AN.

RESULTS

Human CD141+ DCs, homologous to murine CD103+ DCs, were significantly increased in patients with FSGS. The number of kidney CD103+ DCs, but not CD103- DCs or plasmacytoid DCs, was significantly decreased in AN mice after AC220 administration. Treatment with AC220 significantly improved kidney function and reduced kidney injury and fibrosis in AN mice. AC220-treated AN mice had decreased levels of inflammatory cytokines and chemokines, tumor necrosis factor-α, interleukin (IL)-1β, IL-6, CCL2 and CCL5 and reduced kidney infiltration of CD4 T cells and CD8 T cells. The protective effect of AC220 was associated with its suppression of CD103+ DCs-mediated CD8 T cell proliferation and activation in AN mice.

CONCLUSION

Flt3 inhibitor AC220 effectively reduced kidney injury in AN mice, suggesting that this inhibitor might be a useful pharmaceutical agent to treat CKD.

Mesenchymal stem cells alleviate rat diabetic nephropathy by suppressing CD103+ DCs-mediated CD8+ T cell responses

Diabetic nephropathy (DN) as a kind of serious microvascular complication of Diabetes Mellitus (DM) usually causes the end‐stage of renal disease (ESRD). Studies have demonstrated that CD103⁺ dendritic cells (DCs) exhibited a renal pathogenic effect in murine chronic kidney disease (CKD). Mesenchymal stem cells (MSCs) can alleviate DN and suppress the DCs maturation. To explore the role of CD103⁺ DCs and the potential mechanisms underlying MSCs‐mediated protective effects in DN, we used bone marrow MSCs (BM‐MSCs) to treat DN rats. MSCs transplantation considerably recovered kidney function and diminished renal injury, fibrosis and the population of renal CD103⁺ DCs in DN rat. The MSCs‐treated DN rats had decreased mRNA expression levels of interleukin (IL)1β, IL6, tumour necrosis factor alpha (TNF‐α), monocyte chemotactic protein 1 (MCP‐1) and reduced CD8 T cell infiltration in the kidney. MSCs significantly down‐regulated the genes expression of transcription factors (Basic leucine zipper transcriptional factor ATF‐like 3, Batf3 and DNA‐binding protein inhibitor ID‐2, Id2) and FMS‐like tyrosine kinase‐3 (Flt3) which are necessary for CD103⁺ DCs development. The protective effect of MSCs may be partly related to their immunosuppression of CD8⁺ T cell proliferation and activation mediated by CD103⁺ DCs in the kidney of DN rats.

Carcinogenesis and Metastasis in Liver: Cell Physiological Basis

Hepatocellular carcinoma (HCC) incidence is rising. This paper summarises the current state of knowledge and recent discoveries in the cellular and physiological mechanisms leading to the development of liver cancer, especially HCC, and liver metastases. After reviewing normal hepatic cytoarchitecture and immunological characteristics, the paper addresses the pathophysiological factors that cause liver damage and predispose to neoplasia. Particular attention is given to chronic liver diseases, metabolic syndrome and the impact of altered gut microbiota, disrupted circadian rhythm and psychological stress. Improved knowledge of the multifactorial aetiology of HCC has important implications for the prevention and treatment of this cancer and of liver metastases in general.

CX3CR1 Mediates the Development of Monocyte-Derived Dendritic Cells during Hepatic Inflammation

Recent evidence suggests that hepatic dendritic cells (HDCs) contribute to the evolution of chronic liver diseases. However, the HDC subsets involved and the mechanisms driving these responses are still poorly understood. In this study, we have investigated the role of the fractalkine receptor CX3CR1 in modulating monocyte-derived dendritic cell (moDC) differentiation during liver inflammation. The phenotype of HDC and functional relevance of CX3CR1 was assessed in mice following necro-inflammatory liver injury induced by the hepatotoxic agent carbon tetrachloride (CCl4) and in steatohepatitis caused by a methionine/choline-deficient (MCD) diet. In both the experimental models, hepatic inflammation was associated with a massive expansion of CD11c+/MHCIIhigh/CD11b+ myeloid HDCs. These cells also expressed the monocyte markers Ly6C, chemokine (C-C Motif) receptor 2 (CCR2), F4/80 and CD88, along with CX3CR1, allowing their tentative identification as moDCs. Mice defective in CX3CR1 showed a reduction in liver-moDC recruitment following CCl4 poisoning in parallel with a defective maturation of monocytes into moDCs. The lack of CX3CR1 also affected moDC differentiation from bone marrow myeloid cells induced by granulocyte-macrophage colony stimulating factor (GM-CSF) and interleukin-4 (IL-4) in vitro. In wild-type mice, treatment with the CX3CR1 antagonist CX3-AT (150 µg, i.p.) 24 h after CCl4 administration reduced liver moDCS and significantly ameliorated hepatic injury and inflammation. Altogether, these results highlight the possible involvement of moDCs in promoting hepatic inflammation following liver injury and indicated a novel role of CX3CL1/CX3CR1 dyad in driving the differentiation of hepatic moDCs.

FLT3/FLT3L-mediated CD103+ dendritic cells alleviates hepatic ischemia-reperfusion injury in mice via activation of treg cells

BACKGROUND

This study was conducted to investigate the protective effect of Fms-like tyrosine kinase 3 (FLT3)/FLT3 ligand (FLT3L)-dependent CD103⁺ dendritic cells (DCs) on hepatic ischemia-reperfusion injury (IRI).

METHODS

A mouse model of hepatic IRI and cellular model following hypoxia-reperfusion (H/R) treatment were established. Peripheral blood and liver tissues were obtained and analyzed by flow cytometer in terms of percentage of CD103⁺DCs and regulatory T (Treg) cells. Serum alanine aminotransferase (ALT), aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) were determined to assess liver function. Moreover, pro-inflammatory cytokines levels including tumor necrosis factor (TNF)-α, interleukin (IL)-1β and IL-6 were measured using enzyme-linked immunosorbent assay (ELISA). The histological morphology of liver tissues was examined with hematoxylin and eosin (HE) staining. The apoptosis was detected by terminal deoxynucleotidyl transferase (TdT) dUTP Nick End Labeling (TUNEL) assay. Treg-associated cytokines transforming growth factor (TGF)-β and IL-10 expressions were measured using quantitative real time polymerase chain reaction (qRT-PCR).

RESULTS

CD103⁺ DCs were significantly decreased in peripheral blood and liver tissues of mouse model of hepatic IRI. In vivo experiments indicated that CD103⁺ DCs infusion ameliorated IRI-induced liver damage and Treg inhibition. Further investigations demonstrated that FLT3/FLT3L-dependent CD103⁺ DCs suppressed hepatocyte apoptosis via activation of Treg cells in vitro.

CONCLUSION

FLT3/FLT3L-induced CD103⁺ DCs alleviated hepatic IRI through activating Treg cells.

Infectious Sporozoites of Plasmodium berghei Effectively Activate Liver CD8α+ Dendritic Cells

Immunization with radiation-attenuated sporozoites (RAS) shown to confer complete sterile protection against Plasmodia liver-stage (LS) infection that lasts about 6 to 9 months in mice. We have found that the intermittent infectious sporozoite challenge to immune mice following RAS vaccination extends the longevity of sterile protection by maintaining CD8⁺ T cell memory responses to LS infection. It is reported that CD8α⁺ dendritic cells (DCs) are involved in the induction of LS-specific CD8⁺ T cells following RAS or genetically attenuated parasite (GAP) vaccination. In this study, we demonstrate that CD8α⁺ DCs respond differently to infectious sporozoite or RAS inoculation. The higher accumulation and activation of CD8α⁺ DCs was seen in the liver in response to infectious sporozoite 72 h postinoculation and found to be associated with higher expression of chemokines (CCL-20 and CCL-21) and type I interferon response via toll-like receptor signaling in liver. Moreover, the infectious sporozoites were found to induce qualitative changes in terms of the increased MHCII expression as well as costimulatory molecules including CD40 on the CD8α⁺ DCs compared to RAS inoculation. We have also found that infectious sporozoite challenge increased CD40L-expressing CD4⁺ T cells, which could help CD8⁺ T cells in the liver through "licensing" of the antigen-presenting cells. Our results suggest that infectious sporozoite challenge to prior RAS immunized mice modulates the CD8α⁺ DCs, which might be shaping the fate of memory CD8⁺ T cells against Plasmodium LS infection.

Organ-specific mechanisms linking innate and adaptive antifungal immunity

Fungal infections remain a significant global health problem in humans. Fungi infect millions of people worldwide and cause from acute superficial infections to life-threatening systemic disease to chronic illnesses. Trying to decipher the complex innate and adaptive immune mechanisms that protect humans from pathogenic fungi is therefore a key research goal that may lead to immune-based therapeutic strategies and improved patient outcomes. In this review, we summarize how the cells and molecules of the innate immune system activate the adaptive immune system to elicit long-term immunity to fungi. We present current knowledge and exciting new advances in the context of organ-specific immunity, outlining the tissue-specific tropisms for the major pathogenic fungi of humans, the antifungal functions of tissue-resident myeloid cells, and the adaptive immune responses required to protect specific organs from fungal challenge.

Differential Location and Distribution of Hepatic Immune Cells

The liver is one of the main organs in the body, performing several metabolic and immunological functions that are indispensable to the organism. The liver is strategically positioned in the abdominal cavity between the intestine and the systemic circulation. Due to its location, the liver is continually exposed to nutritional insults, microbiota products from the intestinal tract, and to toxic substances. Hepatocytes are the major functional constituents of the hepatic lobes, and perform most of the liver’s secretory and synthesizing functions, although another important cell population sustains the vitality of the organ: the hepatic immune cells. Liver immune cells play a fundamental role in host immune responses and exquisite mechanisms are necessary to govern the density and the location of the different hepatic leukocytes. Here we discuss the location of these pivotal cells within the different liver compartments, and how their frequency and tissular location can dictate the fate of liver immune responses.

The differential organogenesis and functionality of two liver-draining lymph nodes in mice

The liver is an immunological organ. However, fundamental knowledge concerning liver-draining lymph nodes (LNs), which have been newly identified in mice as the portal and celiac LNs, is still lacking. Here, we revealed that the portal LN and celiac LN drain liver lymph through different lymphatic vessels. Although both the portal LN and celiac LN possess typical structures, they have different cell compositions. Interestingly, these two LNs form at different times during fetal development. Moreover, the organogenesis of the celiac LN, but not the portal LN, is controlled by the transcription factor NFIL3. Furthermore, the portal LN and celiac LN also perform different functions. The celiac LN is the predominant site of liver antiviral immune responses, whereas the portal LN functions in the in situ induction of dietary antigen-specific regulatory T cells. In conclusion, the portal LN and celiac LN are two independent liver-draining LNs with different organogenesis histories and separate functions in maintaining immune homeostasis in the liver.

Murine CD103+ dendritic cells protect against steatosis progression towards steatohepatitis

BACKGROUND & AIMS

Non-alcoholic fatty liver (NAFL) is the hepatic consequence of metabolic syndrome and can progress to non-alcoholic steatohepatitis (NASH). The identification of molecular and cellular factors that determine the progression of NASH and lead to irreversible hepatocellular damage are crucial. Dendritic cells (DCs) represent a heterogeneous cell population among which CD103⁺ DCs play a significant role in immunity and tolerance. We aimed to clarify the role of this DC subset in the pathomechanism of NASH.

METHODS

Steatosis progression towards steatohepatitis was analysed using multicolor FACS analyses, cytokine and qPCR array in high sucrose diet (HSD) and methionine and choline deficient diet (MCD) fed wild-type and basic leucine zipper transcription factor, ATF-Like-3 (Batf3) deficient animals, which lack CD103⁺ DCs (classical type-1 DC, cDC1s).

RESULTS

Metabolic challenge of Batf3^-/- animals resulted in the progression of steatosis towards steatohepatitis, manifesting by an increased influx of inflammatory cells into the liver and elevated inflammatory cytokine production of myeloid cells upon innate stimuli. However, the lack of cDC1s did not affect cellular apoptosis and fibrosis progression but altered genes involved in lipid metabolism. The adoptive transfer of CD103⁺ cDC1s to Batf3 deficient animals reversed these observed changes and more importantly could attenuate cellular damage and inflammation in established murine steatohepatitis.

CONCLUSION

Here, we have identified the murine CD103⁺ cDC1s as a protective DC subtype that influences the pro-anti-inflammatory balance and protects the liver from metabolic damage. As guardians of liver integrity, they play a key role in the inflammatory process during the development of steatohepatitis in mice.

LAY SUMMARY

Non-alcoholic fatty liver (NAFL) is the hepatic consequence of metabolic syndrome and can lead to non-alcoholic steatohepatitis (NASH). The current study demonstrated that a specific murine dendritic cell subtype possesses a potent regulatory role to influence the inflammatory milieu of the liver in this process.

Intestinal Batf3-dependent dendritic cells are required for optimal antiviral T-cell responses in adult and neonatal mice

Although we know a great deal about which types of dendritic cells (DCs) promote T-cell priming in the periphery, less is known about which DC subset(s) provoke antiviral responses within the gut. Here we report that conventional Zbtb46-dependent DCs were critically required for antiviral CD8⁺ T-cell responses against rotavirus (RV), the major cause of childhood gastroenteritis worldwide. Furthermore, we found that in adult mice, Batf3-dependent DCs were required for generating optimal RV-specific CD8⁺ T-cell responses. However, in contrast to mice that lack Zbtb46-dependent DCs, a significant amount of interferon gamma-producing RV-specific CD8⁺ T cells were still detected in the small intestine of RV-infected adult Batf3^-/- mice, suggesting the existence of compensatory cross-presentation mechanisms in the absence of Batf3-dependent DCs. In contrast to adult mice, we found that Batf3-dependent DCs were absolutely required for generating RV-specific CD8⁺ T-cell responses in neonates. Loss of Batf3-dependent DCs also resulted in a skewed polyclonal CD4⁺ T-cell response in both adult and neonatal mice upon RV infection, although local and systemic RV-specific immunoglobulin A production kinetics and titers were unimpaired. Our results provide insights that inform early-life vaccination strategies against RV infection.

Dendritic cells from the human female reproductive tract rapidly capture and respond to HIV

Dendritic cells (DCs) throughout the female reproductive tract (FRT) were examined for phenotype, HIV capture ability and innate anti-HIV responses. Two main CD11c⁺ DC subsets were identified: CD11b⁺ and CD11b^low DCs. CD11b⁺CD14⁺ DCs were the most abundant throughout the tract. A majority of CD11c⁺CD14⁺ cells corresponded to CD1c⁺ myeloid DCs, whereas the rest lacked CD1c and CD163 expression (macrophage marker) and may represent monocyte-derived cells. In addition, we identified CD103⁺ DCs, located exclusively in the endometrium, whereas DC-SIGN⁺ DCs were broadly distributed throughout the FRT. Following exposure to GFP-labeled HIV particles, CD14⁺ DC-SIGN⁺ as well as CD14⁺ DC-SIGN^- cells captured virus, with ∼30% of these cells representing CD1c⁺ myeloid DCs. CD103⁺ DCs lacked HIV capture ability. Exposure of FRT DCs to HIV induced secretion of CCL2, CCR5 ligands, interleukin (IL)-8, elafin, and secretory leukocyte peptidase inhibitor (SLPI) within 3 h of exposure, whereas classical pro-inflammatory molecules did not change and interferon-α2 and IL-10 were undetectable. Furthermore, elafin and SLPI upregulation, but not CCL5, were suppressed by estradiol pre-treatment. Our results suggest that specific DC subsets in the FRT have the potential for capture and dissemination of HIV, exert antiviral responses and likely contribute to the recruitment of HIV-target cells through the secretion of innate immune molecules.

Expression of scavenger receptor-AI promotes alternative activation of murine macrophages to limit hepatic inflammation and fibrosis

The liver maintains an immunologically tolerant environment as a result of continuous exposure to food and bacterial constituents from the digestive tract. Hepatotropic pathogens can take advantage of this niche and establish lifelong chronic infections causing hepatic fibrosis and hepatocellular carcinoma. Macrophages (Mϕ) play a critical role in regulation of immune responses to hepatic infection and regeneration of tissue. However, the factors crucial for Mϕ in limiting hepatic inflammation or resolving liver damage have not been fully understood. In this report, we demonstrate that expression of C-type lectin receptor scavenger receptor-AI (SR-AI) is crucial for promoting M2-like Mϕ activation and polarization during hepatic inflammation. Liver Mϕ uniquely up-regulated SR-AI during hepatotropic viral infection and displayed increased expression of alternative Mϕ activation markers, such as YM-1, arginase-1, and interleukin-10 by activation of mer receptor tyrosine kinase associated with inhibition of mammalian target of rapamycin. Expression of these molecules was reduced on Mϕ obtained from livers of infected mice deficient for the gene encoding SR-AI (msr1). Furthermore, in vitro studies using an SR-AI-deficient Mϕ cell line revealed impeded M2 polarization and decreased phagocytic capacity. Direct stimulation with virus was sufficient to activate M2 gene expression in the wild-type (WT) cell line, but not in the knockdown cell line. Importantly, tissue damage and fibrosis were exacerbated in SR-AI^-/- mice following hepatic infection and adoptive transfer of WT bone-marrow-derived Mϕ conferred protection against fibrosis in these mice.

CONCLUSION

SR-AI expression on liver Mϕ promotes recovery from infection-induced tissue damage by mediating a switch to a proresolving Mϕ polarization state. (Hepatology 2017;65:32-43).

Murine liver-resident group 1 innate lymphoid cells regulate optimal priming of anti-viral CD8+ T cells

The liver contains 2 transcriptionally distinct group 1 ILC subsets: CD49a+ ILC1s and CD49b+ NK cells. However, little is known about how group 1 ILCs contribute to hepatic immune responses. Therefore, we characterized murine liver-resident group 1 ILCs and found that CD49a+ ILC1s express high levels of the inhibitory receptor NKG2A and localize near DCs in perivascular spaces surrounding the portal triads. Upon hepatic viral infection, NKG2A signaling in group 1 ILCs, especially in CD49a+ ILC1s, inhibits CXCL9 expression required for robust accumulation of IFN-γ+CD49b+ NK cells. As a consequence, NKG2A-/- mice showed increased numbers of IFN-γ-producing NK cells that preferentially activate liver CD103+ DCs, leading to the sustained proliferation of adoptively transferred, virus-specific CD8+ T cells. Collectively, these data suggest that group 1 ILCs play a role in maintaining the liver as a tolerogenic site by limiting the recruitment of peripheral NK cells during the early phase of viral infection. Furthermore, our findings implicate that the inhibition of NKG2A signaling on group 1 ILCs may be a novel vaccine strategy to induce robust CD8+ T cell responses against persistent liver pathogens.

The Role of Lymphatic Endothelial Cells in Liver Injury and Tumor Development

Lymphatics and lymphatic endothelial cells (LECs) possess multiple immunological functions besides affecting immune cell migration, such as inhibiting T cell proliferation and antigen presentation by dendritic cells. Moreover, they control the trans-endothelial transport of multiple molecules and antigens. Emerging evidence suggest their active involvements in immunregulation, tumor, and metastases formation. In the liver, increased lymphangiogenesis, specifically at the portal area has been associated with multiple liver diseases in particular primary biliary cirrhosis, idiopathic portal hypertension, and liver malignancies. Nevertheless, the exact role and contribution of LECs to liver diseases are poorly understood. The review summarizes the current understanding of LECs in liver diseases.

Intrahepatic regulation of antiviral T cell responses at initial stages of viral infection

It is generally accepted that the appropriate boost of early immune response will control viral replications and limit the immune-mediated pathology in viral hepatitis. However, poor immunity results in viral persistence, chronic inflammation and finally liver cirrhosis and carcinoma. As a peripheral non-lymphoid organ of immune surveillance, the liver continually encounters hundreds of molecules from the blood, including nutrients, toxins and pathogens. In this way, the liver maintains immune tolerance under healthy conditions, but responds quickly to the hepatotropic pathogens during the early stages of an infection. Although our knowledge of liver cell compositions and functions has been improved significantly in recent years, the intrahepatic immune regulation of antiviral T cells at the initial stage is complex and not well elucidated. Here, we summarize the role of liver cell subpopulations in regulating antiviral T cell response at the initial stages of viral infection. A better understanding of early hepatic immune regulation will pave the way for the development of novel therapies and vaccine design for human viral hepatitis.

Biphasic function of TLR3 adjuvant on tumor and spleen dendritic cells promotes tumor T cell infiltration and regression in a vaccine therapy

Successful cancer immunotherapy necessitates T cell proliferation and infiltration into tumor without exhaustion, a process closely links optimal maturation of dendritic cells (DC), and adjuvant promotes this process as an essential prerequisite. Poly(I:C) has contributed to adjuvant immunotherapy that evokes an antitumor response through the Toll-loke receptor 3 (TLR3)/TICAM-1 pathway in DC. However, the mechanism whereby Poly(I:C) acts on DC for T cell proliferation and migration remains undetermined. Subcutaneous injection of Poly(I:C) regressed implant tumors (WT1-C1498 or OVA-EG7) in C57BL/6 mice, which coincided with tumor-infiltration of CD8(+) T cells. Epitope-specific cytotoxic T lymphocytes (CTLs) were increased in spleen by challenge with Poly(I:C)+Db126 WT-1 peptide but not Poly(I:C) alone, suggesting the need of an exogenous Ag density for cross-priming. In tumor, CXCR3 ligands were upregulated by Poly(I:C), which facilitated recruitment of CTL to the tumor. Thus, Poly(I:C) acts on splenic CD8α(+) DC to cross-prime T cells and on intratumor cells to attract CTLs. Besides CD8(+) T cell cross-priming, T cell recruitment into tumor was significantly dampened in Batf3 (-/-) mice, reflecting the importance of tumor Batf3-dependent DC rather than macrophages in T cell recruitment. Poly(I:C)-induced XCR1(hi) CD8α(+) DC with high TLR3 levels were markedly decreased in Batf3 (-/-) mice, which hampered the production of IL-12 and IL-12-mediated CD4(+)/CD8(+) T cell proliferation. Subcutaneous administration of Poly(I:C) and adoptive transfer of wild-type CD8α(+) DC largely recovered antitumor response in those Batf3 (-/-) mice. Collectively, Poly(I:C) tunes up proper maturation of CD8α(+) DC to establish TLR3-mediated IL-12 function and cross-presentation in spleen and lymphocyte-attractive antitumor microenvironment in tumor.

Staying local-antigen presentation in the liver

The liver is known as organ with unique immune competence. Besides its unique microenvironment that is determined by gut-derived portal venous blood constituents and the presence of enzymes with immune regulatory properties, liver antigen presenting cell populations regulate antigen-specific immunity in a local fashion. In addition to bone marrow-derived dendritic cells and myeloid cells such as macrophages and monocytes, also truly liver-resident cell populations function as antigen presenting cells such as liver sinusoidal endothelial cells and hepatocytes. The functional outcome of antigen-presentation by these cell populations is diverse and ranges from generation of regulatory CD4 cells, to induction of memory CD8 T cells or deletional tolerance, which generates a complex network of antigen-presenting cells that determines hepatic immune regulation and local immune surveillance against viral infection.

Crosstalk between innate and adaptive immunity in hepatitis B virus infection

Hepatitis B virus (HBV) infection is a major public health problem worldwide. HBV is not directly cytotoxic to infected hepatocytes; the clinical outcome of infection results from complicated interactions between the virus and the host immune system. In acute HBV infection, initiation of a broad, vigorous immune response is responsible for viral clearance and self-limited inflammatory liver disease. Effective and coordinated innate and adaptive immune responses are critical for viral clearance and the development of long-lasting immunity. Chronic hepatitis B patients fail to mount efficient innate and adaptive immune responses to the virus. In particular, HBV-specific cytotoxic T cells, which are crucial for HBV clearance, are hyporesponsiveness to HBV infection. Accumulating experimental evidence obtained from the development of animal and cell line models has highlighted the importance of innate immunity in the early control of HBV spread. The virus has evolved immune escape strategies, with higher HBV loads and HBV protein concentrations associated with increasing impairment of immune function. Therefore, treatment of HBV infection requires inhibition of HBV replication and protein expression to restore the suppressed host immunity. Complicated interactions exist not only between innate and adaptive responses, but also among innate immune cells and different components of adaptive responses. Improved insight into these complex interactions are important in designing new therapeutic strategies for the treatment HBV infection. In this review, we summarize the current knowledge regarding the cross-talk between the innate and adaptive immune responses and among different immunocytes in HBV infection.

The complex myeloid network of the liver with diverse functional capacity at steady state and in inflammation

In recent years, it has been an explosion of information regarding the role of various myeloid cells in liver pathology. Macrophages and dendritic cell (DC) play crucial roles in multiple chronic liver diseases such as fibrosis and non-alcoholic fatty liver disease (NAFLD). The complexity of myeloid cell populations and the missing exclusive marker combination make the interpretation of the data often extremely difficult. The current review aims to summarize the multiple roles of macrophages and DCs in chronic liver diseases, especially pointing out how these cells influence liver immune and parenchymal cells thereby altering liver function and pathology. Moreover, the review outlines the currently known marker combinations for the identification of these cell populations for the study of their role in liver immunology.