T cells protect against hepatitis A virus infection and limit infection-induced liver injury

Activation of bystander CD8+ T cells in a pediatric patient with acute hepatitis E

Most children with acute hepatitis A virus (HAV) or hepatitis E virus (HEV) infection are asymptomatic. Bystander CD8+ T-cell activation has garnered attention owing to its possible pathophysiological role in adult hepatitis. However, no reports have studied it in pediatric hepatitis. Herein, we describe the case of a three-year-old girl with acute hepatitis by HEV genotype 1. She had a history of Epstein-Barr virus (EBV) and cytomegalovirus (CMV) infections, and HEV hepatitis occurred shortly after asymptomatic HAV infection. Peripheral immunophenotyping revealed activation of non-HEV-specific CD8+ T cells which include EBV-specific and CMV-specific CD8+ T cells, during the acute phase. While alanine-aminotransferase levels declined after admission, the total number of activated CD8+ T cells increased for four days after admission and decreased thereafter. In contrast, activation of EBV-specific and CMV-specific CD8+ T cells was almost at the maximal level at the time of admission, which suggest development of activated bystander CD8+ T cells in the early stage. This case highlights the significance of the bystander CD8+ T-cell activation even in pediatric hepatitis and the size of the CD8+ T cell memory pool in the individuals for the development of hepatitis, given the patient's history of infections with EBV, CMV and HAV.

LncRNA taurine upregulated gene 1 in liver disease

Long non-coding RNAs (lncRNAs) are RNA sequences exceeding 200 nucleotides in length that lack protein-coding capacity and participate in diverse biological processes in the human body, particularly exerting a pivotal role in disease surveillance, diagnosis, and progression. Taurine upregulated gene 1 (TUG1) is a versatile lncRNA, and recent studies have revealed that the aberrant expression or function of TUG1 is intricately linked to the pathogenesis of liver diseases. Consequently, we have summarized the current understanding of the mechanism of TUG1 in liver diseases such as liver fibrosis, fatty liver, cirrhosis, liver injury, hepatitis, and liver cancer. Moreover, mounting evidence suggests that interventions targeting TUG1 or its downstream pathways may hold therapeutic promise for liver diseases. This review elucidates the characteristics, mechanisms, and targets of TUG1 in liver diseases, offering a theoretical basis for the prevention, diagnosis, treatment, and prognostic biomarkers of liver diseases.

Mathematical modeling of endogenous and exogenously administered T cell recirculation in mouse and its application to pharmacokinetic studies of cell therapies

Introduction

In vivo T cell migration has been of interest to scientists for the past 60 years. T cell kinetics are important in the understanding of the immune response to infectious agents. More recently, adoptive T cell therapies have proven to be a most promising approach to treating a wide range of diseases, including autoimmune and cancer diseases, whereby the characterization of cellular kinetics represents an important step towards the prediction of therapeutic efficacy.

Methods

Here, we developed a physiologically-based pharmacokinetic (PBPK) model that describes endogenous T cell homeostasis and the kinetics of exogenously administered T cells in mouse. Parameter calibration was performed using a nonlinear fixed-effects modeling approach based on published data on T cell kinetics and steady-state levels in different tissues of mice. The Partial Rank Correlation Coefficient (PRCC) method was used to perform a global sensitivity assessment. To estimate the impact of kinetic parameters on exogenously administered T cell dynamics, a local sensitivity analysis was conducted.

Results

We simulated the model to analyze cellular kinetics following various T cell doses and frequencies of CCR7+ T cells in the population of infused lymphocytes. The model predicted the effects of T cell numbers and of population composition of infused T cells on the resultant concentration of T cells in various organs. For example, a higher percentage of CCR7+ T cells among exogenously administered T lymphocytes led to an augmented accumulation of T cells in the spleen. The model predicted a linear dependence of T cell dynamics on the dose of adoptively transferred T cells.

Discussion

The mathematical model of T cell migration presented here can be integrated into a multi-scale model of the immune system and be used in a preclinical setting for predicting the distribution of genetically modified T lymphocytes in various organs, following adoptive T cell therapies.

Biochemical analysis of the host factor activity of ZCCHC14 in hepatitis A virus replication

Relatively little is known of the mechanisms underlying hepatitis A virus (HAV) genome replication. Unlike other well-studied picornaviruses, HAV RNA replication requires the zinc finger protein ZCCHC14 and non-canonical TENT4 poly(A) polymerases with which it forms a complex. The ZCCHC14-TENT4 complex binds to a stem-loop located within the internal ribosome entry site (IRES) in the 5' untranslated RNA (5'UTR) and is essential for viral RNA synthesis, but the underlying mechanism is unknown. Here, we describe how different ZCCHC14 domains contribute to its RNA-binding, TENT4-binding, and HAV host factor activities. We show that the RNA-binding activity of ZCCHC14 requires both a sterile alpha motif (SAM) and a downstream unstructured domain (D4) and that ZCCHC14 contains two TENT4-binding sites: one at the N-terminus and the other around D4. Both RNA-binding and TENT4-binding are required for HAV host factor activity of ZCCHC14. We also demonstrate that the location of the ZCCHC14-binding site within the 5'UTR is critical for its function. Our study provides a novel insight into the function of ZCCHC14 and helps elucidate the mechanism of the ZCCHC14-TENT4 complex in HAV replication.IMPORTANCEThe zinc finger protein ZCCHC14 is an essential host factor for both hepatitis A virus (HAV) and hepatitis B virus (HBV). It recruits the non-canonical TENT4 poly(A) polymerases to viral RNAs and most likely also a subset of cellular mRNAs. Little is known about the details of these interactions. We show here the functional domains of ZCCHC14 that are involved in binding to HAV RNA and interactions with TENT4 and describe previously unrecognized peptide sequences that are critical for the HAV host factor activity of ZCCHC14. Our study advances the understanding of the ZCCHC14-TENT4 complex and how it functions in regulating viral and cellular RNAs.

Hepatitis A virus infection

Hepatitis A is a vaccine-preventable infection caused by the hepatitis A virus (HAV). Over 150 million new infections of hepatitis A occur annually. HAV causes an acute inflammatory reaction in the liver that usually resolves spontaneously without chronic sequelae. However, up to 20% of patients experience a prolonged or relapsed course and <1% experience acute liver failure. Host factors, such as immunological status, age, pregnancy and underlying hepatic diseases, can affect the severity of disease. Anti-HAV IgG antibodies produced in response to HAV infection persist for life and protect against re-infection; vaccine-induced antibodies against hepatitis A confer long-term protection. The WHO recommends vaccination for individuals at higher risk of infection and/or severe disease in countries with very low and low hepatitis A virus endemicity, and universal childhood vaccination in intermediate endemicity countries. To date, >25 countries worldwide have implemented such programmes, resulting in a reduction in the incidence of HAV infection. Improving hygiene and sanitation, rapid identification of outbreaks and fast and accurate intervention in outbreak control are essential to reducing HAV transmission.

Reverse Vaccinology and Immunoinformatic Approach for Designing a Bivalent Vaccine Candidate Against Hepatitis A and Hepatitis B Viruses

Hepatitis A and B are two crucial viral infections that still dramatically affect public health worldwide. Hepatitis A Virus (HAV) is the main cause of acute hepatitis, whereas Hepatitis B Virus (HBV) leads to the chronic form of the disease, possibly cirrhosis or liver failure. Therefore, vaccination has always been considered the most effective preventive method against pathogens. At this moment, we aimed at the immunoinformatic analysis of HAV-Viral Protein 1 (VP1) as the major capsid protein to come up with the most conserved immunogenic truncated protein to be fused by HBV surface antigen (HBs Ag) to achieve a bivalent vaccine against HAV and HBV using an AAY linker. Various computational approaches were employed to predict highly conserved regions and the most immunogenic B-cell and T-cell epitopes of HAV-VP1 capsid protein in both humans and BALB/c. Moreover, the predicted fusion protein was analyzed regarding primary and secondary structures and also homology validation. Afterward, the three-dimensional structure of vaccine constructs docked with various toll-like receptors (TLR) 2, 4 and 7. According to the bioinformatics tools, the region of 99-259 amino acids of VP1 was selected with high immunogenicity and conserved epitopes. T-cell epitope prediction showed that this region contains 32 antigenic peptides for Human leukocyte antigen (HLA) class I and 20 antigenic peptides in terms of HLA class II which are almost fully conserved in the Iranian population. The vaccine design includes 5 linear and 4 conformational B-cell lymphocyte (BCL) epitopes to induce humoral immune responses. The designed VP1-AAY-HBsAg fusion protein has the potency to be constructed and expressed to achieve a bivalent vaccine candidate, especially in the Iranian population. These findings led us to claim that the designed vaccine candidate provides potential pathways for creating an exploratory vaccine against Hepatitis A and Hepatitis B Viruses with high confidence for the identified strains.

Comparison of HAV and HCV infections in vivo and in vitro reveals distinct patterns of innate immune evasion and activation

BACKGROUND & AIMS

Hepatitis A virus (HAV) infections are considered not to trigger innate immunity in vivo, in contrast to hepatitis C virus (HCV). This lack of induction has been imputed to strong interference by HAV proteases 3CD and 3ABC. We aimed to elucidate the mechanisms of immune activation and counteraction by HAV and HCV in vivo and in vitro.

METHODS

Albumin-urokinase-type plasminogen activator/severe combined immunodeficiency (Alb/uPA-SCID) mice with humanised livers were infected with HAV and HCV. Hepatic cell culture models were used to assess HAV and HCV sensing by Toll-like receptor 3 and retinoic acid-inducible gene I/melanoma differentiation-associated protein 5 (RIG-I/MDA5), respectively. Cleavage of the adaptor proteins TIR-domain-containing adapter-inducing interferon-β (TRIF) and mitochondrial antiviral-signalling protein (MAVS) was analysed by transient and stable expression of HAV and HCV proteases and virus infection.

RESULTS

We detected similar levels of interferon-stimulated gene induction in hepatocytes of HAV- and HCV-infected mice with humanised liver. In cell culture, HAV induced interferon-stimulated genes exclusively upon MDA5 sensing and depended on LGP2 (laboratory of genetics and physiology 2). TRIF and MAVS were only partially cleaved by HAV 3ABC and 3CD, not sufficiently to abrogate signalling. In contrast, HCV NS3-4A efficiently degraded MAVS, as previously reported, whereas TRIF cleavage was not detected.

CONCLUSIONS

HAV induces an innate immune response in hepatocytes via MDA5/LGP2, with limited control of both pathways by proteolytic cleavage. HCV activates Toll-like receptor 3 and lacks TRIF cleavage, suggesting that this pathway mainly contributes to HCV-induced antiviral responses in hepatocytes. Our results shed new light on the induction of innate immunity and counteraction by HAV and HCV.

IMPACT AND IMPLICATIONS

Understanding the mechanisms that determine the differential outcomes of HAV and HCV infections is crucial for the development of effective therapies. Our study provides insights into the interplay between these viruses and the host innate immune response in vitro and in vivo, shedding light on previously controversial or only partially investigated aspects. This knowledge could tailor the development of new strategies to combat HCV persistence, as well as improve our understanding of the factors underlying successful HAV clearance.

Studying T Cell Responses to Hepatotropic Viruses in the Liver Microenvironment

T cells play an important role in the clearance of hepatotropic viruses but may also cause liver injury and contribute to disease progression in chronic hepatitis B and C virus infections which affect millions of people worldwide. The liver provides a unique microenvironment of immunological tolerance and hepatic immune regulation can modulate the functional properties of T cell subsets and influence the outcome of a virus infection. Extensive research over the last years has advanced our understanding of hepatic conventional CD4+ and CD8+ T cells and unconventional T cell subsets and their functions in the liver environment during acute and chronic viral infections. The recent development of new small animal models and technological advances should further increase our knowledge of hepatic immunological mechanisms. Here we provide an overview of the existing models to study hepatic T cells and review the current knowledge about the distinct roles of heterogeneous T cell populations during acute and chronic viral hepatitis.

Viral protease cleavage of MAVS in genetically modified mice with hepatitis A virus infection

BACKGROUND & AIMS

Consistent with its relatively narrow host species range, hepatitis A virus (HAV) cannot infect C57BL/6 mice. However, in Mavs-/- mice with genetic deficiency of the innate immune signaling adaptor MAVS, HAV replicates robustly in the absence of disease. The HAV 3ABC protease cleaves MAVS in human cells, thereby disrupting virus-induced IFN responses, but it cannot cleave murine MAVS (mMAVS) due to sequence differences at the site of scission. Here, we sought to elucidate the role of 3ABC MAVS cleavage in determining HAV pathogenesis and host species range.

METHODS

Using CRISPR/Cas9 gene editing, we established two independent lineages of C57BL/6 mice with knock-in mutations altering two amino acids in mMAVS ('mMAVS-VS'), rendering it susceptible to 3ABC cleavage without loss of signaling function. We challenged homozygous Mavsvs/vs mice with HAV, and compared infection outcomes with C57BL/6 and genetically deficient Mavs-/- mice.

RESULTS

The humanized murine mMAVS-VS protein was cleaved as efficiently as human MAVS when co-expressed with 3ABC in Huh-7 cells. In embyronic fibroblasts from Mavsvs/vs mice, mMAVS-VS was cleaved by ectopically expressed 3ABC, significantly disrupting Sendai virus-induced IFN responses. However, in contrast to Mavs-/- mice with genetic MAVS deficiency, HAV failed to establish infection in Mavsvs/vs mice, even with additional genetic knockout of Trif or Irf1. Nonetheless, when crossed with permissive Ifnar1-/- mice lacking type I IFN receptors, Mavsvs/vsIfnar1-/- mice demonstrated enhanced viral replication coupled with significant reductions in serum alanine aminotransferase, hepatocellular apoptosis, and intrahepatic inflammatory cell infiltrates compared with Ifnar1-/- mice.

CONCLUSIONS

MAVS cleavage by 3ABC boosts viral replication and disrupts disease pathogenesis, but it is not by itself sufficient to break the host-species barrier to HAV infection in mice.

IMPACT AND IMPLICATIONS

The limited host range of human hepatitis viruses could be explained by species-specific viral strategies that disrupt innate immune responses. Both hepatitis A virus (HAV) and hepatitis C virus express viral proteases that cleave the innate immune adaptor protein MAVS, in human but not mouse cells. However, the impact of this immune evasion strategy has never been assessed in vivo. Here we show that HAV 3ABC protease cleavage of MAVS enhances viral replication and lessens liver inflammation in mice lacking interferon receptors, but that it is insufficient by itself to overcome the cross-species barrier to infection in mice. These results enhance our understanding of how hepatitis viruses interact with the host and their impact on innate immune responses.

Hepatitis A: Viral Structure, Classification, Life Cycle, Clinical Symptoms, Diagnosis Error, and Vaccination

Hepatitis A virus (HAV) is one of the well-known viruses that cause hepatitis all around the globe. Although this illness has decreased in developed countries due to extensive immunization, numerous developing and under-developed countries are struggling with this virus. HAV infection can be spread by oral-fecal contact, and there are frequent epidemics through nutrition. Improvements in socioeconomic and sanitary circumstances have caused a shift in the disease's prevalence worldwide. Younger children are usually asymptomatic, but as they become older, the infection symptoms begin to appear. Symptoms range from slight inflammation and jaundice to acute liver failure in older individuals. While an acute infection may be self-limiting, unrecognized persistent infections, and the misapplication of therapeutic methods based on clinical guidelines are linked to a higher incidence of cirrhosis, hepatocellular carcinoma, and mortality. Fortunately, most patients recover within two months of infection, though 10-15% of patients will relapse within the first six months. A virus seldom leads to persistent infection or liver damage. The mainstay of therapy is based on supportive care. All children from 12-23 months, as well as some susceptible populations, should receive routine vaccinations, according to the Centers for Disease Control and Prevention and the American Academy of Pediatrics. Laboratory diagnosis of HAV is based on antigen detection, checking liver enzyme levels, and antibody screening. Furthermore, polymerase chain reaction (PCR) technology has identified HAV in suspected nutrition sources; therefore, this technique is used for preventative measures and food-related laws.

Macrophage Depletion Reactivates Fecal Virus Shedding following Resolution of Acute Hepatitis A in Ifnar1-/- Mice

Although hepatitis A virus (HAV) is associated only with acute hepatitis in humans, HAV RNA persists within the liver for months following resolution of liver inflammation and cessation of fecal virus shedding in chimpanzees and murine models of hepatitis A. Here, we confirm striking differences in the kinetics of HAV RNA clearance from liver versus serum and feces in infected Ifnar1-/- mice and investigate the nature of viral RNA persisting in the liver following normalization of serum alanine aminotransferase (ALT) levels. Fecal shedding of virus produced in hepatocytes declined >3,000-fold between its peak at day 14 and day 126, whereas intrahepatic HAV RNA declined only 32-fold by day 154. Viral RNA was identified within hepatocytes 3 to 4 months after inoculation and was associated with membranes, banding between 1.07 and 1.14 g/cm3 in isopycnic iodixanol gradients. Gradient fractions containing HAV RNA demonstrated no infectivity when inoculated into naive mice but contained neutralizing anti-HAV antibody. Depleting CD4+ or CD8+ T cells at this late point in infection had no effect on viral RNA abundance in the liver, whereas clodronate-liposome depletion of macrophages between days 110 and 120 postinoculation resulted in a striking recrudescence of fecal virus shedding and the reappearance of viral RNA in serum coupled with reductions in intra-hepatic Ifnγ, Tnfα, Ccl5, and other chemokine transcripts. Our data suggest that replication-competent HAV RNA persists for months within the liver in the presence of neutralizing antibody following resolution of acute hepatitis in Ifnar1-/- mice and that macrophages play a key role in viral control late in infection. IMPORTANCE HAV RNA persists in the liver of infected chimpanzees and interferon receptor-deficient Ifnar1-/- mice for many months after neutralizing antibodies appear, virus has been cleared from the blood, and fecal virus shedding has terminated. Here, we show this viral RNA is located within hepatocytes and that the depletion of macrophages months after the resolution of hepatic inflammation restores fecal virus shedding and circulating viral RNA. Our study identifies an important role for macrophages in virus control following resolution of acute hepatitis A in Ifnar1-/- mice and may have relevance to relapsing hepatitis A in humans.

The immunological mechanisms and therapeutic potential in drug-induced liver injury: lessons learned from acetaminophen hepatotoxicity

Acute liver failure caused by drug overdose is a significant clinical problem in developed countries. Acetaminophen (APAP), a widely used analgesic and antipyretic drug, but its overdose can cause acute liver failure. In addition to APAP-induced direct hepatotoxicity, the intracellular signaling mechanisms of APAP-induced liver injury (AILI) including metabolic activation, mitochondrial oxidant stress and proinflammatory response further affect progression and severity of AILI. Liver inflammation is a result of multiple interactions of cell death molecules, immune cell-derived cytokines and chemokines, as well as damaged cell-released signals which orchestrate hepatic immune cell infiltration. The immunoregulatory interplay of these inflammatory mediators and switching of immune responses during AILI lead to different fate of liver pathology. Thus, better understanding the complex interplay of immune cell subsets in experimental models and defining their functional involvement in disease progression are essential to identify novel therapeutic targets for the treatment of AILI. Here, this present review aims to systematically elaborate on the underlying immunological mechanisms of AILI, its relevance to immune cells and their effector molecules, and briefly discuss great therapeutic potential based on inflammatory mediators.

The infectivity and pathogenicity of Hepatitis A virus live-attenuated vaccine strain H2 in type I interferon receptor-deficient mice

Hepatitis A virus (HAV) live-attenuated vaccine H2 strain has been approved for clinical use for decades with ideal safety profiles in nonhuman primate models and humans. Recently, type I interferon (IFN) receptor-deficient mice were shown to be susceptible to HAV infection. Herein, we sought to determine the infection and replication dynamics of the H2 in Ifnar^−/− mice that lack type I IFN receptor. Following intravenous injection, the H2 failed to cause obvious clinical symptoms in Ifnar^−/− mice, and no significant upregulation in serum alanine aminotransferase (ALT) levels was observed. Notably, the histopathological examination showed that there were significant focal infiltrations of lymphocytes and neutrophils in the portal area, but no focal necrosis was observed in liver tissues. Viral RNAs sustained in the liver, and the infectious virus could be recovered from the liver tissue until 42 days post-infection. More importantly, H2 infection induced obvious viremia and persistent viral shedding in feces. In addition, robust HAV-specific humoral immune responses were induced in Ifnar^−/− mice. Overall, our study revealed the safety profile of H2 in Ifnar^−/− mice, which not only helps understand the attenuation mechanism of H2, but also expands the application of the Ifnar^−/− mouse model for HAV studies.

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We described the characteristics of Ifnar−/− mice infected by HAV H2 strain infection.

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H2 fails to induce ALT elevationand obvious liver damage in Ifnar−/− mice.

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H2 causes viremia, persistent viral shedding in feces, and replication in mice liver.

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H2 induces robust HAV-specific humoral immune responses in Ifnar^−/− mice.

The ZCCHC14/TENT4 complex is required for hepatitis A virus RNA synthesis

Despite excellent vaccines, resurgent outbreaks of hepatitis A have caused thousands of hospitalizations and hundreds of deaths within the United States in recent years. There is no effective antiviral therapy for hepatitis A, and many aspects of the hepatitis A virus (HAV) replication cycle remain to be elucidated. Replication requires the zinc finger protein ZCCHC14 and noncanonical TENT4 poly(A) polymerases with which it associates, but the underlying mechanism is unknown. Here, we show that ZCCHC14 and TENT4A/B are required for viral RNA synthesis following translation of the viral genome in infected cells. Cross-linking immunoprecipitation sequencing (CLIP-seq) experiments revealed that ZCCHC14 binds a small stem-loop in the HAV 5' untranslated RNA possessing a Smaug recognition-like pentaloop to which it recruits TENT4. TENT4 polymerases lengthen and stabilize the 3' poly(A) tails of some cellular and viral mRNAs, but the chemical inhibition of TENT4A/B with the dihydroquinolizinone RG7834 had no impact on the length of the HAV 3' poly(A) tail, stability of HAV RNA, or cap-independent translation of the viral genome. By contrast, RG7834 inhibited the incorporation of 5-ethynyl uridine into nascent HAV RNA, indicating that TENT4A/B function in viral RNA synthesis. Consistent with potent in vitro antiviral activity against HAV (IC₅₀ 6.11 nM), orally administered RG7834 completely blocked HAV infection in Ifnar1^-/- mice, and sharply reduced serum alanine aminotransferase activities, hepatocyte apoptosis, and intrahepatic inflammatory cell infiltrates in mice with acute hepatitis A. These results reveal requirements for ZCCHC14-TENT4A/B in hepatovirus RNA synthesis, and suggest that TENT4A/B inhibitors may be useful for preventing or treating hepatitis A in humans.

The Roles and Pathogenesis Mechanisms of a Number of Micronutrients in the Prevention and/or Treatment of Chronic Hepatitis, COVID-19 and Type-2 Diabetes Mellitus

A trace element is a chemical element with a concentration (or other measures of an amount) that is very low. The essential TEs, such as copper (Cu), selenium (Se), zinc (Zn), iron (Fe) and the electrolyte magnesium (Mg) are among the most commonly studied micronutrients. Each element has been shown to play a distinctive role in human health, and TEs, such as iron (Fe), zinc (Zn) and copper (Cu), are among the essential elements required for the organisms' well-being as they play crucial roles in several metabolic pathways where they act as enzyme co-factors, anti-inflammatory and antioxidant agents. Epidemics of infectious diseases are becoming more frequent and spread at a faster pace around the world, which has resulted in major impacts on the economy and health systems. Different trace elements have been reported to have substantial roles in the pathogenesis of viral infections. Micronutrients have been proposed in various studies as determinants of liver disorders, COVID-19 and T2DM risks. This review article sheds light on the roles and mechanisms of micronutrients in the pathogenesis and prevention of chronic hepatitis B, C and E, as well as Coronavirus-19 infection and type-2 diabetes mellitus. An update on the status of the aforementioned micronutrients in pre-clinical and clinical settings is also briefly summarized.

Humoral and cellular immune memory response 12 years following single dose vaccination against hepatitis A in Argentinian children

Infants' universal hepatitis A virus (HAV) single-dose vaccination has been highly effective for controlling HAV infection in Argentina, and in other Latin-American countries that adopted that strategy. Although antibodies wane over time, this has not been associated with HAV outbreaks or breakthrough infections, suggesting a relevant role for memory immunity. This study assessed long term humoral and cellular immune memory response after an average of 12 years follow-up of HAV single-dose vaccination. We selected 81 HAV-single dose vaccinated individuals from a 2015 study, including 54 with unprotective (UAL) and 27 with protective antibody levels (PAL) against HAV. Humoral memory response was assessed by measuring anti-HAV antibody titers at admission in both groups, and 30 days after a booster dose in the UAL group. Flow cytometry analysis of peripheral blood mononuclear cell samples stimulated with HAV antigen was performed in 47/81 individuals (21 with PAL, 26 with UAL) to identify activated CD4 + memory T cells or CD8 + memory T cells. The results showed that 48/52 (92%) individuals from UAL group who completed follow up reached protective levels after booster dose. In the PAL group, anti-HAV Abs waned in 2/27 (7%) individuals lacking seroprotection, while in 25/27 (93%) Abs remained >10 mUI/mL. HAV-specific memory CD4 + T cells were detected in 25/47 (53.2%) subjects while HAV-specific memory CD8 + T cells were observed in 16/47 (34.04%) individuals. HAV-specific memory CD4⁺ and CD8⁺ T cell responses were detected in 11/21 (52.4%) and in 9/21 (42.9%) subjects with PAL and in 14/26 (53.8%) and in 7/26 (26.9%) individuals with UAL, showing that the presence of memory T-cells was independent of the level or presence of anti-HAV antibodies. Long-term immunity demonstrated in the present work, including or not antibody persistence, suggests that individuals with waned Ab titers may still be protected and supports the single-dose HAV strategy.

IRF3-mediated pathogenicity in a murine model of human hepatitis A

HAV-infected Ifnar1^-/- mice recapitulate many of the cardinal features of hepatitis A in humans, including serum alanine aminotransferase (ALT) elevation, hepatocellular apoptosis, and liver inflammation. Previous studies implicate MAVS-IRF3 signaling in pathogenesis, but leave unresolved the role of IRF3-mediated transcription versus the non-transcriptional, pro-apoptotic activity of ubiquitylated IRF3. Here, we compare the intrahepatic transcriptomes of infected versus naïve Mavs^-/- and Ifnar1^-/- mice using high-throughput sequencing, and identify IRF3-mediated transcriptional responses associated with hepatocyte apoptosis and liver inflammation. Infection was transcriptionally silent in Mavs^-/- mice, in which HAV replicates robustly within the liver without inducing inflammation or hepatocellular apoptosis. By contrast, infection resulted in the upregulation of hundreds of genes in Ifnar1^-/- mice that develop acute hepatitis closely modeling human disease. Upregulated genes included pattern recognition receptors, interferons, chemokines, cytokines and other interferon-stimulated genes. Compared with Ifnar1^-/- mice, HAV-induced inflammation was markedly attenuated and there were few apoptotic hepatocytes in livers of infected Irf3^S1/S1Ifnar1^-/- mice in which IRF3 is transcriptionally-inactive due to alanine substitutions at Ser-388 and Ser-390. Although transcriptome profiling revealed remarkably similar sets of genes induced in Irf3^S1/S1Ifnar1^-/- and Ifnar1^-/- mice, a subset of genes was differentially expressed in relation to the severity of the liver injury. Prominent among these were both type 1 and type III interferons and interferon-responsive genes associated previously with apoptosis, including multiple members of the ISG12 and 2’-5’ oligoadenylate synthetase families. Ifnl3 and Ifnl2 transcript abundance correlated strongly with disease severity, but mice with dual type 1 and type III interferon receptor deficiency remained fully susceptible to liver injury. Collectively, our data show that IRF3-mediated transcription is required for HAV-induced liver injury in mice and identify key IRF3-responsive genes associated with pathogenicity, providing a clear distinction from the transcription-independent role of IRF3 in liver injury following binge exposure to alcohol.

Hepatitis A is a common and potentially serious disease involving inflammation and liver cell death resulting from infection with the picornavirus, hepatitis A virus (HAV). The pathogenesis of the disease is incompletely understood. Here, we have profiled changes in the RNA transcriptome of livers from mice with various genetic deficiencies in the innate immune response to HAV. We show that the liver injury associated with HAV infection in these mice results from the induction of genes under transcriptional control of interferon regulatory factor 3 (IRF3). We use high-throughput RNA sequencing to identify sets of genes induced in mice with wild-type versus transcriptionally-incompetent IRF3, rule out roles for type III interferons and IFIT proteins in disease pathogenesis, and identify genes with intrahepatic expression correlating closely with HAV-mediated liver pathology.