Expression of B and T lymphocyte attenuator (BTLA) in macrophages contributes to the fulminant hepatitis caused by murine hepatitis virus strain-3

HSP70 contributes to pathogenesis of fulminant hepatitis induced by coronavirus

Fulminant viral hepatitis (FH) represents a significant clinical challenge, with its pathogenesis not yet fully elucidated. Heat shock protein (HSP)70, a molecular chaperone protein with a broad range of cytoprotective functions, is upregulated in response to stress. However, the role of HSP70 in FH remains to be investigated. Notably, HSP70 expression is upregulated in the livers of coronavirus-infected mice and patients. Therefore, we investigated the mechanistic role of HSP70 in coronavirus-associated FH pathogenesis. FH was induced in HSP70-deficient (HSP70 KO) mice or in WT mice treated with the HSP70 inhibitor VER155008 when infected with the mouse hepatitis virus strain A59 (MHV-A59). MHV-A59-infected HSP70 KO mice exhibited significantly reduced liver damage and mortality. This effect was attributed to decreased infiltration of monocyte-macrophages and neutrophils in the liver of HSP70 KO mice, resulting in lower levels of inflammatory cytokines such as IL-1β, TNFα, and IL-6, and a reduced viral load. Moreover, treatment with the HSP70 inhibitor VER155008 protected mice from MHV-A59-induced liver damage and FH mortality. In summary, HSP70 promotes coronavirus-induced FH pathogenesis by enhancing the infiltration of monocyte-macrophages and neutrophils and promoting the secretion of inflammatory cytokines. Therefore, HSP70 is a potential therapeutic target in viral FH intervention.

The effect of rs2910686 on ERAP2 expression in IBD and epithelial inflammatory response

BACKGROUND

ERAP2 is an aminopeptidase involved in antigen processing and presentation, and harbor genetic variants linked to several inflammatory diseases such as Inflammatory Bowel Disease (IBD). The lack of an ERAP2 gene homologue in mice has hampered functional studies, and most human studies have focused on cells of hematopoietic origin. Using an IBD biobank as vantage point, this study explores how genetic variation in ERAP2 affects gene expression in human-derived epithelial organoids upon proinflammatory stimulation.

METHODS

An IBD patient cohort was genotyped with regards to two single nucleotide polymorphisms (SNP) (rs2910686/rs2248374) associated with ERAP2 expression levels, and we examined the correlation between colon gene expression and genotype, specifically aiming to establish a relationship with ERAP2 expression proficiency. Human-derived colon organoids (colonoids) with known ERAP2 genotype were established and used to explore differences in whole genome gene expression between ERAP2-deficient (n = 4) and -proficient (n = 4) donors upon pro-inflammatory encounter.

RESULTS

When taking rs2910686 genotype into account, ERAP2 gene expression is upregulated in the inflamed colon of IBD patients. Colonoids upregulate ERAP2 upon IFNɣ stimulation, and ERAP2 expression proficiency is dependent on rs2910686 genotype. Colonoid genotyping confirms that mechanisms independent of the frequently studied SNP rs2248374 can cause ERAP2-deficiency. A total of 586 genes involved in various molecular mechanisms are differentially expressed between ERAP2 proficient- and deficient colonoids upon proinflammatory stimulation, including genes encoding proteins with the following molecular function: catalytic activity (AOC1, CPE, ANPEP and MEP1A), regulator activity (TNFSF9, MDK, GDF15, ILR6A, LGALS3 and FLNA), transmembrane transporter activity (SLC40A1 and SLC5A1), and extracellular matrix structural constituents (FGL2, HMCN2, and MUC17).

CONCLUSIONS

ERAP2 is upregulated in the inflamed IBD colon mucosa, and expression proficiency is highly correlated with genotype of rs2910686. While the SNP rs2248374 is commonly used to determine ERAP2 expressional proficiency, our data confirms that mechanisms independent of this SNP can lead to ERAP2 deficiency. Our data demonstrates that epithelial ERAP2 presence affects the inflammatory response in colonoids, suggesting a pleiotropic role of ERAP2 beyond MHC class I antigen processing.

FGL2 improves experimental colitis related to gut microbiota structure and bile acid metabolism by regulating macrophage autophagy and apoptosis

Inflammatory bowel disease (IBD) is a refractory disease with immune abnormalities and pathological changes. Intestinal macrophages are considered to be the main factor in establishing and maintaining intestinal homeostasis. The immunoregulatory and anti-inflammatory activity of fibrinogen-like protein 2 (FGL2) can regulate macrophage polarization. However, its function in IBD is unclear. In this study, we explored the effect of FGL2 on macrophage polarization, autophagy, and apoptosis in bone marrow-derived macrophages (BMDMs) treated with lipopolysaccharide (LPS) and further investigated changes in the intestinal barrier, flora, and bile acid in dextran sodium sulfate (DSS)-treated mice. Our results demonstrated that FGL2-/- weakened ERK signaling to promote M1 polarization and upregulate inflammation, autophagy, and apoptosis in LPS-stimulated BMDMs. rFGL2 treatment reversed these effects. FGL2-/- mice exhibited higher sensitivity to DSS exposure, with faster body weight loss, shorter colon lengths, and higher disease activity index (DAI) values. rFGL2 treatment protected against experimental ulcerative colitis (UC), restrained excessive autophagy, apoptosis, and improved gut barrier impairment. Gut microbiota structure and bile acid homeostasis were more unbalanced in FGL2-/- DSS mice than in wild-type (WT) DSS mice. rFGL2 treatment improved gut microbiota structure and bile acid homeostasis. Altogether, our results established that FGL2 is a potential therapeutic target for IBD.

FGL1 and FGL2: emerging regulators of liver health and disease

Liver disease is a complex group of diseases with high morbidity and mortality rates, emerging as a major global health concern. Recent studies have highlighted the involvement of fibrinogen-like proteins, specifically fibrinogen-like protein 1 (FGL1) and fibrinogen-like protein 2 (FGL2), in the regulation of various liver diseases. FGL1 plays a crucial role in promoting hepatocyte growth, regulating lipid metabolism, and influencing the tumor microenvironment (TME), contributing significantly to liver repair, non-alcoholic fatty liver disease (NAFLD), and liver cancer. On the other hand, FGL2 is a multifunctional protein known for its role in modulating prothrombin activity and inducing immune tolerance, impacting viral hepatitis, liver fibrosis, hepatocellular carcinoma (HCC), and liver transplantation. Understanding the functions and mechanisms of fibrinogen-like proteins is essential for the development of effective therapeutic approaches for liver diseases. Additionally, FGL1 has demonstrated potential as a disease biomarker in radiation and drug-induced liver injury as well as HCC, while FGL2 shows promise as a biomarker in viral hepatitis and liver transplantation. The expression levels of these molecules offer exciting prospects for disease assessment. This review provides an overview of the structure and roles of FGL1 and FGL2 in different liver conditions, emphasizing the intricate molecular regulatory processes and advancements in targeted therapies. Furthermore, it explores the potential benefits and challenges of targeting FGL1 and FGL2 for liver disease treatment and the prospects of fibrinogen-like proteins as biomarkers for liver disease, offering insights for future research in this field.

BTLA contributes to acute-on-chronic liver failure infection and mortality through CD4+ T-cell exhaustion

B- and T-lymphocyte attenuator (BTLA) levels are increased in patients with hepatitis B virus-related acute-on-chronic liver failure (HBV-ACLF). This condition is characterized by susceptibility to infection and T-cell immune exhaustion. However, whether BTLA can induce T-cell immune exhaustion and increase the risk of infection remains unclear. Here, we report that BTLA levels are significantly increased in the circulating and intrahepatic CD4+ T cells from patients with HBV-ACLF, and are positively correlated with disease severity, prognosis, and infection complications. BTLA levels were upregulated by the IL-6 and TNF signaling pathways. Antibody crosslinking of BTLA activated the PI3K-Akt pathway to inhibit the activation, proliferation, and cytokine production of CD4+ T cells while promoting their apoptosis. In contrast, BTLA knockdown promoted their activation and proliferation. BTLA-/- ACLF mice exhibited increased cytokine secretion, and reduced mortality and bacterial burden. The administration of a neutralizing anti-BTLA antibody reduced Klebsiella pneumoniae load and mortality in mice with ACLF. These data may help elucidate HBV-ACLF pathogenesis and aid in identifying novel drug targets.

FGL2 promotes tumour growth and attenuates infiltration of activated immune cells in melanoma and ovarian cancer models

The tumour microenvironment is infiltrated by immunosuppressive cells, such as regulatory T cells (Tregs), which contribute to tumour escape and impede immunotherapy outcomes. Soluble fibrinogen-like protein 2 (sFGL2), a Treg effector protein, inhibits immune cell populations, via receptors FcγRIIB and FcγRIII, leading to downregulation of CD86 in antigen presenting cells and limiting T cell activation. Increased FGL2 expression is associated with tumour progression and poor survival in several different cancers, such as glioblastoma multiforme, lung, renal, liver, colorectal, and prostate cancer. Querying scRNA-seq human cancer data shows FGL2 is produced by cells in the tumour microenvironment (TME), particularly monocytes and macrophages as well as T cells and dendritic cells (DCs), while cancer cells have minimal expression of FGL2. We studied the role of FGL2 exclusively produced by cells in the TME, by leveraging Fgl2 knockout mice. We tested two murine models of cancer in which the role of FGL2 has not been previously studied: epithelial ovarian cancer and melanoma. We show that absence of FGL2 leads to a more activated TME, including activated DCs (CD86+, CD40+) and T cells (CD25+, TIGIT+), as well as demonstrating for the first time that the absence of FGL2 leads to more activated natural killer cells (DNAM-1+, NKG2D+) in the TME. Furthermore, the absence of FGL2 leads to prolonged survival in the B16F10 melanoma model, while the absence of FGL2 synergizes with oncolytic virus to prolong survival in the ID8-p53-/-Brca2-/- ovarian cancer model. In conclusion, targeting FGL2 is a promising cancer treatment strategy alone and in combination immunotherapies.

Dapagliflozin alleviates renal inflammation and protects against diabetic kidney diseases, both dependent and independent of blood glucose levels

Introduction

Diabetic kidney disease (DKD) has become the leading cause of end-stage renal disease worldwide. Therefore, efforts to understand DKD pathophysiology and prevent its development at the early phase are highly warranted.

Methods

Here, we analyzed kidneys from healthy mice, diabetic mice, and diabetic mice treated with the sodium-glucose cotransporter 2 inhibitor dapagliflozin using ATAC and RNA sequencing. The findings were verified at the protein levels and in cultured cells.

Results

Our combined method of ATAC and RNA sequencing revealed Csf2rb, Btla, and Isg15 as the key candidate genes associated with hyperglycemia, azotemia, and albuminuria. Their protein levels were altered together with multiple other inflammatory cytokines in the diabetic kidney, which was alleviated by dapagliflozin treatment. Cell culture of immortalized renal tubular cells and macrophages unraveled that dapagliflozin could directly effect on these cells in vitro as an anti-inflammatory agent independent of glucose concentrations. We further proved that dapagliflozin attenuated ischemia/reperfusion-induced chronic kidney injury and renal inflammation in mice.

Discussion

Overall, our data emphasize the importance of inflammatory factors to the pathogenesis of DKD, and provide valuable mechanistic insights into the renoprotective role of dapagliflozin.

Harnessing the immune system by targeting immune checkpoints: Providing new hope for Oncotherapy

With the goal of harnessing the host's immune system to provide long-lasting remission and cures for various cancers, the advent of immunotherapy revolutionized the cancer therapy field. Among the current immunotherapeutic strategies, immune checkpoint blockades have greatly improved the overall survival rates in certain patient populations. Of note, CTLA4 and PD-1/PD-L1 are two major non-redundant immune checkpoints implicated in promoting cancer immune evasion, and ultimately lead to relapse. Antibodies or inhibitors targeting these two c+heckpoints have achieved some encouraging clinical outcomes. Further, beyond the canonical immune checkpoints, more inhibitory checkpoints have been identified. Herein, we will summarize recent progress in immune checkpoint blockade therapies, with a specific focus on key pre-clinical and clinical results of new immune checkpoint therapies for cancer. Given the crucial roles of immune checkpoint blockade in oncotherapy, drugs targeting checkpoint molecules expressed by both cancer and immune cells are in clinical trials, which will be comprehensively summarized in this review. Taken together, investigating combinatorial therapies targeting immune checkpoints expressed by cancer cells and immune cells will greatly improve immunotherapies that enhance host elimination of tumors.

FGL2-MCOLN3-Autophagy Axis-Triggered Neutrophil Extracellular Traps Exacerbate Liver Injury in Fulminant Viral Hepatitis

BACKGROUND & AIMS

Fulminant viral hepatitis (FVH) is a life-threatening disease, but its pathogenesis is not fully understood. Neutrophil extracellular traps (NETs) were an unrecognized link between inflammation and coagulation, which are 2 main features of FVH. Here, we investigated the role and mechanism of NETs in the pathogenesis of FVH.

METHODS

A mouse model of FVH was established by murine hepatitis virus strain-3 infection. Liver leukocytes of infected or uninfected mice were used for single-cell RNA sequencing and whole-transcriptome sequencing. NETs depletion was achieved using DNase 1. Acetaminophen was used to establish a mouse model of non-virus-caused acute liver failure. Clinically, NETs-related markers in liver, plasma, and peripheral neutrophils were assessed in patients with hepatitis B virus (HBV)-related acute liver injury.

RESULTS

Increased hepatic NETs formation was observed in murine hepatitis virus strain-3-infected mice, but not in acetaminophen-treated mice. NETs depletion improved the liver damage and survival rate in FVH by inhibiting hepatic fibrin deposition and inflammation. An adoptive transfer experiment showed that neutrophil-specific fibrinogen-like protein 2 (FGL2) promoted NETs formation. FGL2 was found to directly interact with mucolipin 3, which regulated calcium influx and initiated autophagy, leading to NETs formation. Clinically, increased plasma NETs level was associated with coagulation dysfunction in patients with HBV acute liver injury. Colocalization of FGL2, NETs, and fibrin in liver was observed in these patients.

CONCLUSIONS

NETs aggravated liver injury in FVH by promoting fibrin deposition and inflammation. NETs formation was regulated by the FGL2-mucolipin 3-autophagy axis. Targeting NETs may provide a new strategy for the treatment of FVH.

Fibrinogen-like protein 2 deficiency inhibits virus-induced fulminant hepatitis through abrogating inflammatory macrophage activation

BACKGROUND

Heterogeneous macrophages play an important role in multiple liver diseases, including viral fulminant hepatitis (VFH). Fibrinogen-like protein 2 (FGL2) is expressed on macrophages and regulates VFH pathogenesis; however, the underlying mechanism remains unclear.

AIM

To explore how FGL2 regulates macrophage function and subsequent liver injury during VFH.

METHODS

Murine hepatitis virus strain 3 (MHV-3) was used to induce VFH in FGL2-deficient (Fgl2-/-) and wild-type (WT) mice. The dynamic constitution of hepatic macrophages was examined. Adoptive transfer of Fgl2-/- or WT bone marrow-derived macrophages (BMDMs) into WT recipients with macrophages depleted prior to infection was carried out and the consequent degree of liver damage was compared. The signaling cascades that may be regulated by FGL2 were detected in macrophages.

RESULTS

Following MHV-3 infection, hepatic macrophages were largely replenished by proinflammatory monocyte-derived macrophages (MoMFs), which expressed high levels of FGL2. In Fgl2-/- mice, the number of infiltrating inflammatory MoMFs was reduced compared with that in WT mice after viral infection. Macrophage depletion ameliorated liver damage in WT mice and further alleviated liver damage in Fgl2-/- mice. Adoptive transfer of Fgl2-/- BMDMs into macrophage-removed recipients significantly reduced the degree of liver damage. Inhibition of monocyte infiltration also significantly ameliorated liver damage. Functionally, Fgl2 deletion impaired macrophage phagocytosis and the antigen presentation potential and attenuated the proinflammatory phenotype. At the molecular level, FGL2 deficiency impaired IRF3, IRF7, and p38 phosphorylation, along with NF-κB activation in BMDMs in response to viral infection.

CONCLUSION

Infiltrated MoMFs represent a major source of hepatic inflammation during VFH progression, and FGL2 expression on MoMFs maintains the proinflammatory phenotype via p38-dependent positive feedback, contributing to VFH pathogenesis.

Roles of BTLA in Immunity and Immune Disorders

B and T lymphocyte attenuator (BTLA) is one of the most important cosignaling molecules. It belongs to the CD28 superfamily and is similar to programmed cell death-1 (PD-1) and cytotoxic T lymphocyte associated antigen-4 (CTLA-4) in terms of its structure and function. BTLA can be detected in most lymphocytes and induces immunosuppression by inhibiting B and T cell activation and proliferation. The BTLA ligand, herpesvirus entry mediator (HVEM), does not belong to the classic B7 family. Instead, it is a member of the tumor necrosis factor receptor (TNFR) superfamily. The association of BTLA with HVEM directly bridges the CD28 and TNFR families and mediates broad and powerful immune effects. Recently, a large number of studies have found that BTLA participates in numerous physiopathological processes, such as tumor, inflammatory diseases, autoimmune diseases, infectious diseases, and transplantation rejection. Therefore, the present work aimed to review the existing knowledge about BTLA in immunity and summarize the diverse functions of BTLA in various immune disorders.

Animal Coronaviruses Induced Apoptosis

Apoptosis is a form of programmed death that has also been observed in cells infected by several viruses. It is considered one of the most critical innate immune mechanisms that limits pathogen proliferation and propagation before the initiation of the adaptive immune response. Recent studies investigating the cellular responses to SARS-CoV and SARS-CoV-2 infection have revealed that coronaviruses can alter cellular homeostasis and promote cell death, providing evidence that the modulation of apoptotic pathways is important for viral replication and propagation. Despite the genetic diversity among different coronavirus clades and the infection of different cell types and several hosts, research studies in animal coronaviruses indicate that apoptosis in host cells is induced by common molecular mechanisms and apoptotic pathways. We summarize and critically review current knowledge on the molecular aspects of cell-death regulation during animal coronaviruses infection and the viral-host interactions to this process. Future research is expected to lead to a better understanding of the regulation of cell death during coronavirus infection. Moreover, investigating the role of viral proteins in this process will help us to identify novel antiviral targets related to apoptotic signaling pathways.

Similarities and Dissimilarities of COVID-19 and Other Coronavirus Diseases

In less than two decades, three deadly zoonotic coronaviruses, severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome coronavirus (MERS-CoV), and SARS-CoV-2, have emerged in humans, causing SARS, MERS, and coronavirus disease 2019 (COVID-19), respectively. The current COVID-19 pandemic poses an unprecedented crisis in health care and social and economic development. It reinforces the cruel fact that CoVs are constantly evolving, possessing the genetic malleability to become highly pathogenic in humans. In this review, we start with an overview of CoV diseases and the molecular virology of CoVs, focusing on similarities and differences between SARS-CoV-2 and its highly pathogenic as well as low-pathogenic counterparts. We then discuss mechanisms underlying pathogenesis and virus-host interactions of SARS-CoV-2 and other CoVs, emphasizing the host immune response. Finally, we summarize strategies adopted for the prevention and treatment of CoV diseases and discuss approaches to develop effective antivirals and vaccines. Expected final online publication date for the Annual Review of Microbiology, Volume 75 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

COVID-19: immunopathogenesis and Immunotherapeutics

The recent novel coronavirus disease (COVID-19) outbreak, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is seeing a rapid increase in infected patients worldwide. The host immune response to SARS-CoV-2 appears to play a critical role in disease pathogenesis and clinical manifestations. SARS-CoV-2 not only activates antiviral immune responses, but can also cause uncontrolled inflammatory responses characterized by marked pro-inflammatory cytokine release in patients with severe COVID-19, leading to lymphopenia, lymphocyte dysfunction, and granulocyte and monocyte abnormalities. These SARS-CoV-2-induced immune abnormalities may lead to infections by microorganisms, septic shock, and severe multiple organ dysfunction. Therefore, mechanisms underlying immune abnormalities in patients with COVID-19 must be elucidated to guide clinical management of the disease. Moreover, rational management of the immune responses to SARS-CoV-2, which includes enhancing anti-viral immunity while inhibiting systemic inflammation, may be key to successful treatment. In this review, we discuss the immunopathology of COVID-19, its potential mechanisms, and clinical implications to aid the development of new therapeutic strategies against COVID-19.

Reduction and Functional Exhaustion of T Cells in Patients With Coronavirus Disease 2019 (COVID-19)

Background: The outbreak of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has posed great threat to human health. T cells play a critical role in antiviral immunity but their numbers and functional state in COVID-19 patients remain largely unclear. Methods: We retrospectively reviewed the counts of T cells and serum cytokine concentration from data of 522 patients with laboratory-confirmed COVID-19 and 40 healthy controls. In addition, the expression of T cell exhaustion markers were measured in 14 COVID-19 cases. Results: The number of total T cells, CD4+ and CD8+ T cells were dramatically reduced in COVID-19 patients, especially in patients requiring Intensive Care Unit (ICU) care. Counts of total T cells, CD8+ T cells or CD4+ T cells lower than 800, 300, or 400/μL, respectively, were negatively correlated with patient survival. T cell numbers were negatively correlated to serum IL-6, IL-10, and TNF-α concentration, with patients in the disease resolution period showing reduced IL-6, IL-10, and TNF-α concentrations and restored T cell counts. T cells from COVID-19 patients had significantly higher levels of the exhausted marker PD-1. Increasing PD-1 and Tim-3 expression on T cells was seen as patients progressed from prodromal to overtly symptomatic stages. Conclusions: T cell counts are reduced significantly in COVID-19 patients, and the surviving T cells appear functionally exhausted. Non-ICU patients with total T cells counts lower than 800/μL may still require urgent intervention, even in the immediate absence of more severe symptoms due to a high risk for further deterioration in condition.

Human genetic basis of fulminant viral hepatitis

In rare cases, hepatitis A virus (HAV) and hepatitis B virus (HBV) can cause fulminant viral hepatitis (FVH), characterized by massive hepatocyte necrosis and an inflammatory infiltrate. Other viral etiologies of FVH are rarer. FVH is life-threatening, but the patients are typically otherwise healthy, and normally resistant to other microbes. Only a small minority of infected individuals develop FVH, and this is the key issue to be addressed for this disease. In mice, mouse hepatitis virus 3 (MHV3) infection is the main model for dissecting FVH pathogenesis. Susceptibility to MHV3 differs between genetic backgrounds, with high and low mortality in C57BL6 and A/J mice, respectively. FVH pathogenesis in mice is related to uncontrolled inflammation and fibrinogen deposition. In humans, FVH is typically sporadic, but rare familial forms also exist, suggesting that there may be causal monogenic inborn errors. A recent study reported a single-gene inborn error of human immunity underlying FVH. A patient with autosomal recessive complete IL-18BP deficiency was shown to have FVH following HAV infection. The mechanism probably involves enhanced IL-18- and IFN-γ-dependent killing of hepatocytes by NK and CD8 T cytotoxic cells. Proof-of-principle that FVH can be genetic is important clinically, for the affected patients and their families, and immunologically, for the study of immunity to viruses in the liver. Moreover, the FVH-causing IL18BP genotype suggests that excessive IL-18 immunity may be a general mechanism underlying FVH, perhaps through the enhancement of IFN-γ immunity.

Clinical significance of circulating soluble immune checkpoint proteins in sorafenib-treated patients with advanced hepatocellular carcinoma

In hepatocellular carcinoma (HCC), the clinical significance of soluble immune checkpoint protein levels as predictors of patient outcomes or therapeutic responses has yet to be defined. This study profiled the baseline levels of sixteen soluble checkpoint proteins and their changes following sorafenib treatment for HCC. Plasma samples were obtained from 53 patients with advanced HCC at baseline, week 1, 2 and 4 of sorafenib treatment and tested the concentrations of 16 soluble checkpoint proteins using multiplexed fluorescent bead-based immunoassays. Multivariate analysis showed high sBTLA levels at baseline were an independent predictor of poor overall survival (p = 0.038). BTLA was highly expressed in T cells and macrophages in peritumoral areas. At week 2, sCD27 levels were decreased compared to baseline. By contrast, the concentrations of most inhibitory proteins, including sBTLA, sLAG-3, sCTLA-4, sPD-1, sCD80, sCD86 and sPD-L1, had significantly increased. The fold-changes of soluble checkpoint receptors and their ligands, including sCTLA-4 with sCD80/sCD86, sPD-1 with sPD-L1; and the fold-changes of sCTLA-4 with sBTLA or sPD-1 were positively correlated. sBTLA may be a good biomarker for predicting overall survival in HCC patients. Sorafenib treatment in patients with advanced HCC revealed dynamic changes of soluble checkpoint protein levels.

Reduction and Functional Exhaustion of T Cells in Patients With Coronavirus Disease 2019 (COVID-19)

Background: The outbreak of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has posed great threat to human health. T cells play a critical role in antiviral immunity but their numbers and functional state in COVID-19 patients remain largely unclear. Methods: We retrospectively reviewed the counts of T cells and serum cytokine concentration from data of 522 patients with laboratory-confirmed COVID-19 and 40 healthy controls. In addition, the expression of T cell exhaustion markers were measured in 14 COVID-19 cases. Results: The number of total T cells, CD4⁺ and CD8⁺ T cells were dramatically reduced in COVID-19 patients, especially in patients requiring Intensive Care Unit (ICU) care. Counts of total T cells, CD8⁺ T cells or CD4⁺ T cells lower than 800, 300, or 400/μL, respectively, were negatively correlated with patient survival. T cell numbers were negatively correlated to serum IL-6, IL-10, and TNF-α concentration, with patients in the disease resolution period showing reduced IL-6, IL-10, and TNF-α concentrations and restored T cell counts. T cells from COVID-19 patients had significantly higher levels of the exhausted marker PD-1. Increasing PD-1 and Tim-3 expression on T cells was seen as patients progressed from prodromal to overtly symptomatic stages. Conclusions: T cell counts are reduced significantly in COVID-19 patients, and the surviving T cells appear functionally exhausted. Non-ICU patients with total T cells counts lower than 800/μL may still require urgent intervention, even in the immediate absence of more severe symptoms due to a high risk for further deterioration in condition.

BTLA/HVEM Signaling: Milestones in Research and Role in Chronic Hepatitis B Virus Infection

B- and T-lymphocyte attenuator (BTLA) is an immune-regulatory receptor, similar to CTLA-4 and PD-1, and is mainly expressed on B-, T-, and all mature lymphocyte cells. Herpes virus entry mediator (HVEM)-BTLA plays a critical role in immune tolerance and immune responses which are areas of intense research. However, the mechanisms of the BTLA and the BTLA/HVEM signaling pathway in human diseases remain unclear. This review describes the research milestones of BTLA and HVEM in chronological order and their role in chronic HBV infection.

Depletion of RIPK1 in hepatocytes exacerbates liver damage in fulminant viral hepatitis

The protein kinase RIPK1 plays a crucial role at the crossroad of stress-induced signaling pathways that affects cell’s decision to live or die. The present study aimed to define the role of RIPK1 in hepatocytes during fulminant viral hepatitis, a worldwide syndrome mainly observed in hepatitis B virus (HBV) infected patients. Mice deficient for RIPK1, specifically in liver parenchymal cells (Ripk1^LPC-KO) and their wild-type littermates (Ripk1^fl/fl), were challenged by either the murine hepatitis virus type 3 (MHV3) or poly I:C, a synthetic analog of double-stranded RNA mimicking viral pathogen-associated molecular pattern. Ripk1^LPC-KO mice developed more severe symptoms at early stage of the MHV3-induced fulminant hepatitis. Similarly, administration of poly I:C only triggered increase of systemic transaminases in Ripk1^LPC-KO mice, reflecting liver damage through induced apoptosis as illustrated by cleaved-caspase 3 labeling of liver tissue sections. Neutralization of TNF-α or prior depletion of macrophages were able to prevent the appearance of apoptosis of hepatocytes in poly I:C-challenged Ripk1^LPC-KO mice. Moreover, poly I:C never induced direct hepatocyte death in primary culture whatever the murine genotype, while it always stimulated an anti-viral response. Our investigations demonstrated that RIPK1 protects hepatocytes from TNF-α secreted from macrophages during viral induced fulminant hepatitis. These data emphasize the potential worsening risks of an HBV infection in people with polymorphism or homozygous amorphic mutations already described for the RIPK1 gene.

Association of biobehavioral factors with non-coding RNAs in cervical cancer

In order to elucidate the mechanisms underlying the biobehavioral factors responsible for cervical cancer from the perspective of lncRNAs. Tumor samples were obtained from patients with stage Ib-IIb squamous cervical cancer, which were divided into high- and low-risk groups according to biobehavioral risk factors. A lncRNA + mRNA microarray was performed, and the results were validated using qRT-PCR. Gene ontology (GO), pathway, and lncRNA-mRNA co-expression analysis were performed to predict the potential functions of the differentially expressed transcripts. 1,621 lncRNAs and 1,345 mRNAs were found to be differentially expressed between the high-risk and low-risk groups. The results of the qR-TPCR validation were in 100% agreement with the microarray analysis results. GO analysis revealed that the transcripts showing significantly different expression were mainly associated with various aspects of immune response. Pathway analysis indicated that systemic lupus erythematosus signaling was the most significantly down-regulated pathway in the high-risk group. Co-expression analysis indicated NONHSAT002712, NONHSAT095060, and TCONS_00026535 had significant correlations with ZNF683 and BTLA, which were found to be associated with the GO term "adaptive immune response". The levels of genome-wide lncRNAs are significantly altered in cervical tumors from patients with higher biobehavioral risk factors.

VSIG4 inhibits proinflammatory macrophage activation by reprogramming mitochondrial pyruvate metabolism

Exacerbation of macrophage-mediated inflammation contributes to pathogenesis of various inflammatory diseases, but the immunometabolic programs underlying regulation of macrophage activation are unclear. Here we show that V-set immunoglobulin-domain-containing 4 (VSIG4), a B7 family-related protein that is expressed by resting macrophages, inhibits macrophage activation in response to lipopolysaccharide. Vsig4 ^-/- mice are susceptible to high-fat diet-caused obesity and murine hepatitis virus strain-3 (MHV-3)-induced fulminant hepatitis due to excessive macrophage-dependent inflammation. VSIG4 activates the PI3K/Akt-STAT3 pathway, leading to pyruvate dehydrogenase kinase-2 (PDK2) upregulation and subsequent phosphorylation of pyruvate dehydrogenase, which results in reduction in pyruvate/acetyl-CoA conversion, mitochondrial reactive oxygen species secretion, and macrophage inhibition. Conversely, interruption of Vsig4 or Pdk2 promotes inflammation. Forced expression of Vsig4 in mice ameliorates MHV-3-induced viral fulminant hepatitis. These data show that VSIG4 negatively regulates macrophage activation by reprogramming mitochondrial pyruvate metabolism.

Enhanced Innate Inflammation Induced by Anti-BTLA Antibody in Dual Insult Model of Hemorrhagic Shock/Sepsis

Sepsis following hemorrhagic shock is a common clinical condition, in which innate immune system suffers from severe suppression. B and T lymphocyte attenuator (BTLA) is an immune-regulatory coinhibitory receptor expressed not only on adaptive, but also on innate immune cells. Our previous data showed that BTLA gene deficient mice were protected from septic mortality when compared with wild-type control C57BL/6 mice. Here, we extended our study by treating C57BL/6 mice with an anti-BTLA monoclonal antibody (clone 6A6; reported to have the ability to neutralize or agonize/potentiate BTLA signaling) in a mouse model of hemorrhagic shock (Hem) followed by sepsis induced by cecal ligation and puncture (CLP); positing initially that if BTLA engagement was neutralized, like gene deficiency, an anti-BTLA mAb would have the similar effects on the inflammatory response/morbidity in these mice after such insults. Here, we report that BTLA expression is elevated on innate immune cells after Hem/CLP. However, anti-BTLA antibody treatment increased cytokine (TNF-α, IL-12, IL-10)/chemokine (KC, MIP-2, MCP-1) levels and inflammatory cells (neutrophils, macrophages, dendritic cells) recruitment in the peritoneal cavity, which in turn aggravated organ injury and elevated these animals' mortality in Hem/CLP. When compared with the protective effects of our previous study using BTLA gene deficient mice in a model of lethal septic challenge, we further confirmed BTLA's contribution to enhanced innate cell recruitment, elevated IL-10 levels, and reduced survival, and that engagement of antibody with BTLA potentiates/exacerbates the pathophysiology in Hem/sepsis.

The NLRP3 Inflammasome and IL-1β Accelerate Immunologically Mediated Pathology in Experimental Viral Fulminant Hepatitis

Viral fulminant hepatitis (FH) is a severe disease with high mortality resulting from excessive inflammation in the infected liver. Clinical interventions have been inefficient due to the lack of knowledge for inflammatory pathogenesis in the virus-infected liver. We show that wild-type mice infected with murine hepatitis virus strain-3 (MHV-3), a model for viral FH, manifest with severe disease and high mortality in association with a significant elevation in IL-1β expression in the serum and liver. Whereas, the viral infection in IL-1β receptor-I deficient (IL-1R1^-/-) or IL-1R antagonist (IL-1Ra) treated mice, show reductions in virus replication, disease progress and mortality. IL-1R1 deficiency appears to debilitate the virus-induced fibrinogen-like protein-2 (FGL2) production in macrophages and CD45⁺Gr-1^high neutrophil infiltration in the liver. The quick release of reactive oxygen species (ROS) by the infected macrophages suggests a plausible viral initiation of NLRP3 inflammasome activation. Further experiments show that mice deficient of p47^phox, a nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunit that controls acute ROS production, present with reductions in NLRP3 inflammasome activation and subsequent IL-1β secretion during viral infection, which appears to be responsible for acquiring resilience to viral FH. Moreover, viral infected animals in deficiencies of NLRP3 and Caspase-1, two essential components of the inflammasome complex, also have reduced IL-1β induction along with ameliorated hepatitis. Our results demonstrate that the ROS/NLRP3/IL-1β axis institutes an essential signaling pathway, which is over activated and directly causes the severe liver disease during viral infection, which sheds light on development of efficient treatments for human viral FH and other severe inflammatory diseases.

The NLRP3 inflammasome and IL-1β play essential roles in mediating the primary inflammatory responses against pathogen invasions in the host. Hyperactivation of this signaling pathway can lead to life-threatening diseases under certain circumstances. However, it is not clear if NLRP3 inflammasome activation participates in the pathogenesis of viral fulminant hepatitis (FH), a clinical severe syndrome characterized by acute inflammation in the liver along with massive necrosis of hepatocytes and hepatic encephalopathy during viral infection. Using a mouse viral FH model by infection with murine hepatitis virus strain-3 (MHV-3), we observed a significant macrophage induction and the serum and liver massive accumulation of IL-1β. Conversely, interruption of IL-1β signals results in attenuation of the MHV-3-induced hepatitis and mortality. Blocking IL-1β activity reduces the virus-induced expression of fibrinogen-like protein-2 (FGL2) in macrophages, and limits the liver recruitment of CD45⁺Gr-1^high neutrophils upon the virus infection. We further show that proIL-1β is bioprocessed by NLRP3 inflammasome. Deletion of the components in the inflammasome complex, including NLRP3 and Caspase-1, leads to reduction in the virus-induced IL-1β production and lessening of disease progression. Further studies show that macrophages in deficiency of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunit p47^phox, a protein that controls acute ROS production, prevents NLRP3 inflammasome activation and IL-1β secretion, suggesting that the virus-induced ROS production can directly initiate NLRP3 inflammasome activation. Therefore, p47^phox-/- mice exhibited certain degrees of MHV-3 resistance. Taken together, these results demonstrate that ROS/NLRP3/IL-1β is the key pathway signaling exacerbated inflammatory responses that cause viral FH in mice, suggesting that mediation of this signal cascade may benefit on the disease treatment.

C5aR, TNF-α, and FGL2 contribute to coagulation and complement activation in virus-induced fulminant hepatitis

BACKGROUND & AIMS

Viral fulminant hepatitis (FH) is a disease with a high mortality rate. Activation of the complement system correlates with the development of FH. However, the key factors mediating complement activation in FH remain elusive.

METHODS

Liver tissues were isolated from FH patients infected by hepatitis B virus (HBV) and from mice infected with murine hepatitis virus strain 3 (MHV-3). Wild type mice were treated with or without antagonists of C5aR or TNF-α, and mice deficient for C5aR (C5aR(-/-)), Fgl2 (Fgl2(-/-)), and Tnfα (Tnfα(-/-)) mice were not treated with the antagonists. C5b-9, C5aR, FGL2, CD31, CD11b, fibrin, TNF-α, and complement C3 cleavage products were detected by immunohistochemistry, immunofluorescence, or ELISA. Sorted liver sinusoidal endothelial cells (LSECs) or myeloid-derived (CD11b(+)) cells were stimulated with C5a, TNF-α or MHV-3 in vitro. The mRNA expressions levels of Fgl2 and Tnfα were determined by qRT-PCR analyses.

RESULTS

We observed that complement activation, coagulation and pro-inflammatory cytokine production were upregulated in the HBV(+) patients with FH. Similar observations were made in the murine FH models. Complement activation and coagulation were significantly reduced in MHV-3 infected mice in the absence of C5aR, Tnfα or Fgl2. The MHV-3 infected C5aR(-/-) mice exhibited reduced numbers of infiltrated inflammatory CD11b(+) cells and a reduced expression of TNF-α and FGL2. Moreover, C5a administration stimulated TNF-α production by CD11b(+) cells, which in turn promoted the expression of FGL2 in CD31(+) LSEC-like cells in vitro. Administration of antagonists against C5aR or TNF-α ameliorated MHV-3-induced FH.

CONCLUSIONS

Our results demonstrate that C5aR, TNF-α, and FGL2 form an integral network that contributes to coagulation and complement activation, and suggest that those are potential therapeutic targets in viral FH intervention.

The Duality of Fgl2 - Secreted Immune Checkpoint Regulator Versus Membrane-Associated Procoagulant: Therapeutic Potential and Implications

Fibrinogen-like protein 2 (Fgl2), a member of the fibrinogen family, can be expressed as a membrane-associated protein with coagulation activity or in a secreted form possessing unique immune suppressive functions. The biological importance of Fgl2 is evident within viral-induced fibrin depositing inflammatory diseases and malignancies and provides a compelling rationale for Fgl2 expression to not only be considered as a disease biomarker but also as a therapeutic target. This article will provide a comprehensive review of the currently known biological properties of Fgl2 and clarifies future scientific directives.

C5a/C5aR pathway is essential for the pathogenesis of murine viral fulminant hepatitis by way of potentiating Fgl2/fibroleukin expression

Viral fulminant hepatitis (FH) remains a serious clinical problem with very high mortality. Lacking understanding of FH pathogenesis has in essence hindered efficient clinical treatment. Inferring from a correlation observed between the genetic differences in the complement component 5 (C5) and the susceptibility of mouse strains to murine hepatitis virus strain-3 (MHV-3) infections, we propose that excessive complement activation plays a critical role in the development of FH. We show that MHV-3 infection causes massive complement activation, along with a rapid increase in serum C5a levels and quick development of FH in susceptible strains. Mice deficient in the C5a receptor (C5aR) or the susceptible strains treated with C5aR antagonists (C5aRa) exhibit significant attenuation of the disease, accompanied by a remarkable reduction of hepatic fibrinogen-like protein 2 (Fgl2), a hallmark protein that causes necrosis of infected livers. In accordance, biopsy of FH patients shows a dramatic increase of Fgl2 expression, which correlates with C5aR up-regulation in the liver. In vitro C5a administration accelerates MHV-3-induced Fgl2 secretion by macrophages. Furthermore, inhibiting ERK1/2 and p38 efficiently blocks C5a-mediated Fgl2 production during viral infections.

CONCLUSION

These data provide evidence that mouse susceptibility to MHV-3-induced FH may rely on C5a/C5aR interactions, for which ERK1/2 and p38 pathways participate in up-regulating Fgl2 expression. Inhibition of C5a/C5aR interactions is expected to be beneficial in the clinical treatment of FH patients.

Tumor necrosis factor α (TNF-α) receptor-I is required for TNF-α-mediated fulminant virus hepatitis caused by murine hepatitis virus strain-3 infection

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TNFR1^−/− mice displayed a dramatic decrease in tissue necrosis and cell apoptosis in the MHV-3 infected spleens and livers.

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TNFR1 deficiency directly impeded FGL2 secretion as well as reduced Fas and FasL expression in MHV-3 infected livers.

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TNFR1 deficiency impeded neutrophils, which produce proinflammatory factors and FGL2 directly, infiltration into liver and spleen.

TNF-α plays an essential role in the pathogenesis of fulminant virus hepatitis (FH) caused by infection with murine hepatitis virus strain-3 (MHV-3). However, the specific TNF-α receptors (TNFR) involved in this disease and how they mediate this effect are uncertain. Here, we showed that the expression of TNFR1 and TNFR2 in the liver and spleen was triggered by MHV-3. However, only TNFR1^−/− mice were resistant to MHV-3 mediated FH, as displayed by a dramatic decrease in tissue necrosis and cell apoptosis in the infected spleens and livers from TNFR1^−/− mice, as well as prolonged survival in these mice compared to wild type littermate controls. Mechanistically, TNFR1 deficiency directly impeded the serum and tissue levels of fibrinogen-like protein 2 (FGL2), a virus-induced procoagulant molecule that promotes cell apoptosis. Additionally, the expression of apoptosis-associated molecules, Fas and Fas ligand (FasL) in the infected organs from TNFR1^−/− mice were also decreased. Moreover, the infiltration of neutrophils rather than Foxp3⁺ regulatory T cells, which produce proinflammatory factors and FGL2 directly, into the infected liver and spleen tissues was also decreased in TNFR1^−/− mice. These combined results indicate that signaling through TNFR1 plays an essential role in the pathogenesis of FH caused by MHV-3 infection, and interruption of this signaling pathway could be useful for clinical therapy.

Physiological functions and clinical implications of fibrinogen-like 2: A review

Fibrinogen-like 2 (FGL2) encompasses a transmembrane (mFGL2) and a soluble (sFGL2) form with differential tertiary structure and biological activities. Typically, mFGL2 functions as prothrombinase that is capable of initiating coagulation in tissue without activation of the blood clotting cascade, whereas sFGL2 largely acts as an immunosuppressor that can repress proliferation of alloreactive T lymphocytes and maturation of bone marrow dendritic cells. Protein sequences of FGL2 exhibit evolutionary conservation across wide variety of species, especially at the carboxyl terminus that contains fibrinogen related domain (FRED). The FRED of FGL2 confers specificity and complexity in the action of FGL2, including receptor recognition, calcium affiliation, and substrate binding. Constitutive expression of FGL2 during embryogenesis and in mature tissues suggests FGL2 might be physiologically important. However, excessive induction of FGL2 under certain medical conditions (e.g., pathogen invasion) could trigger complement activation, inflammatory response, cellular apoptosis, and immune dysfunctions. On the other hand, complete absence of FGL2 is also detrimental as lack of FGL2 can cause autoimmune glomerulonephritis and acute cellular rejection of xenografts. All these roles involve mFGL2, sFGL2, or their combination. Although it is not clear how mFGL2 is cleaved off its host cells and secreted into the blood, circulating sFGL2 has been found correlated with disease severity and viral loading among patients with human hepatitis B virus or hepatitis C virus infection. Further studies are warranted to understand how FGL2 expression is regulated under physiological and pathological conditions. Even more interesting is to determine whether mFGL2 can fulfill an immunoregulatory role through its FRED at carboxyl end of the molecule and, and vice versa, whether sFGL2 is procoagulant upon binding to a target cell. Knowledge in this area should shed light on development of sFGL2 as an alternative immunosuppressive agent for organ transplantation or as a biomarker for predicting disease progression, monitoring therapeutic effects, and targeting FGL2 for repression in ameliorating fulminant viral hepatitis.

The intrahepatic expression and distribution of BTLA and its ligand HVEM in patients with HBV-related acute-on-chronic liver failure

Objective

It has been demonstrated that signals from the inhibitory receptor B and T lymphocyte attenuator (BTLA) are involved in regulating the pathogenesis of infectious diseases. However, the expression and anatomical distribution of BTLA and its ligand, the herpes virus entry mediator (HVEM), have not yet been determined in cases of HBV-related acute-on-chronic liver failure (HBV-ACLF) patients.

Methods

In this study, the expression of BTLA and HVEM in liver tissues from HBV-ACLF, chronic hepatitis B (CHB) patients and healthy individuals was analyzed by immunohistochemistry.

Results

The results of this analysis demonstrated that both molecules were observed in the HBV-ACLF samples and that their expression was chiefly in the infiltrating inflammatory cells and the damaged bile ducts. However, they were absent in liver sections from CHB patients and healthy controls. Immunofluorescence double-staining indicated that BTLA was found on CK-18⁺ epithelial cells, CD31⁺ endothelial cells, CD68⁺ macrophages, CD56⁺ NK cells, CD16⁺ monocytes, CD3⁺ , CD8⁺ T cells, and Foxp3⁺ regulatory T cells (Treg). By contrast, HVEM expression was restricted to CK18⁺ epithelial cells and CD68⁺ macrophages. Moreover, the expression of several members of the B7 superfamily, including PD-L1, PD-L2, B7-H3 and B7-H4, was also detected in these liver tissues, and these proteins were co-expressed with HVEM. Interestingly, the expression of fibrinogen-like protein 2 (FGL2), a virus-induced procoagulant molecule, was also found in liver sections from HBV-ACLF, this molecule also co-expresses with BTLA and HVEM.

Conclusions

These results suggest that BTLA-HVEM signaling is likely to affect the pathogenesis of HBV-ACLF, a clear understanding of the functional roles of these proteins should further elucidate the disease process.

Virtual slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/8080806838149123