CXCL10 is produced in hepatitis A virus-infected cells in an IRF3-dependent but IFN-independent manner

The Role of Interferon Regulatory Factors in Liver Diseases

The interferon regulatory factors (IRFs) family comprises 11 members that are involved in various biological processes such as antiviral defense, cell proliferation regulation, differentiation, and apoptosis. Recent studies have highlighted the roles of IRF1-9 in a range of liver diseases, including hepatic ischemia-reperfusion injury (IRI), alcohol-induced liver injury, Con A-induced liver injury, nonalcoholic fatty liver disease (NAFLD), cirrhosis, and hepatocellular carcinoma (HCC). IRF1 is involved in the progression of hepatic IRI through signaling pathways such as PIAS1/NFATc1/HDAC1/IRF1/p38 MAPK and IRF1/JNK. The regulation of downstream IL-12, IL-15, p21, p38, HMGB1, JNK, Beclin1, β-catenin, caspase 3, caspase 8, IFN-γ, IFN-β and other genes are involved in the progression of hepatic IRI, and in the development of HCC through the regulation of PD-L1, IL-6, IL-8, CXCL1, CXCL10, and CXCR3. In addition, IRF3-PPP2R1B and IRF4-FSTL1-DIP2A/CD14 pathways are involved in the development of NAFLD. Other members of the IRF family also play moderately important functions in different liver diseases. Therefore, given the significance of IRFs in liver diseases and the lack of a comprehensive compilation of their molecular mechanisms in different liver diseases, this review is dedicated to exploring the molecular mechanisms of IRFs in various liver diseases.

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.

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.

Intrahepatic infiltration of activated CD8+ T cells and mononuclear phagocyte is associated with idiosyncratic drug-induced liver injury

Background

Idiosyncratic drug-induced liver injury (DILI) is caused by the interplay among drugs, their metabolites, and the host immune response. The characterization of infiltrated immune cells in the liver may improve the understanding of the pathogenesis of idiosyncratic DILI. This study investigated the phenotypes and clinical implications of liver-infiltrating immune cells in idiosyncratic DILI.

Methods

From January 2017 to June 2021, 53 patients with idiosyncratic DILI who underwent liver biopsy were prospectively enrolled in this study. Immunohistochemical staining and flow cytometry analyses were performed on the biopsy specimens. Serum levels of CXC chemokine ligand 10 (CXCL10) and soluble CD163 were measured. A multivariate cox proportional hazards model was used to evaluate predictors of DILI resolution within 30 days.

Results

The numbers of intrahepatic T cells and mononuclear phagocytes were positively correlated with serum levels of total bilirubin, alanine aminotransferase (ALT), and the model of end-stage liver disease score. The frequency of activated CD8+ T cells among liver-infiltrating CD8+ T cells in DILI livers was higher than that in healthy livers. Notably, the percentages of activated intrahepatic CD8+ T cells and mononuclear phagocytes in DILI livers showed a positive correlation with ALT. Additionally, serum CXCL10 level was positively correlated with intrahepatic T cell infiltration and ALT, and soluble CD163 level was positively correlated with intrahepatic mononuclear phagocyte infiltration and ALT. Thirty-six patients (70.6%) were treated with steroids. In multivariate analysis, total bilirubin and steroid use independently influenced DILI resolution within 30 days.

Conclusions

Activated CD8+ T cells and mononuclear phagocyte are associated with liver injury caused by drugs. Therefore, we suggest that steroids are a potential treatment option for idiosyncratic DILI.

Effects of Bacillus subtilis Natto Strains on Antiviral Responses in Resiquimod-Stimulated Human M1-Phenotype Macrophages

Bacillus subtilis natto is used in the production of natto, a traditional fermented soy food, and has beneficial immunomodulatory effects in humans. Single-stranded RNA (ssRNA) viruses, including influenza and coronavirus, often cause global pandemics. We proposed a human cell culture model mimicking ssRNA viral infection and investigated the ability of B. subtilis natto to induce antiviral effects in the model. The gene expressions were analyzed using quantitative real-time reverse transcription PCR. M1-phenotype macrophages derived from THP-1 cells strongly express the Toll-like receptor 8 (76.2-hold), CD80 (64.2-hold), and CCR7 (45.7-hold) mRNA compared to M0 macrophages. One µg/mL of resiquimod (RSQ)-stimulation induced the expression of IRF3 (1.9-hold), CXCL10 (14.5-hold), IFNβ1 (3.5-hold), ISG20 (4.4-hold), and MxA (1.7-hold) mRNA in the M1-phenotype macrophages. Based on these results, the RSQ-stimulated M1-phenotype macrophages were used as a cell culture model mimicking ssRNA viral infection. Moreover, the B. subtilis natto XF36 strain induced the expression of genes associated with antiviral activities (IFNβ1, IFNλ1, ISG20, and RNase L) and anti-inflammatory activities (IL-10) in the cell culture model. Thus, it is suggested that the XF36 suppresses viral infections and excessive inflammation by inducing the expression of genes involved in antiviral and anti-inflammatory activities.

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.

CXCL10 Chemokine: A Critical Player in RNA and DNA Viral Infections

Chemokines constitute a group of small, secreted proteins that regulate leukocyte migration and contribute to their activation. Chemokines are crucial inflammatory mediators that play a key role in managing viral infections, during which the profile of chemokine expression helps shape the immune response and regulate viral clearance, improving clinical outcome. In particular, the chemokine ligand CXCL10 and its receptor CXCR3 were explored in a plethora of RNA and DNA viral infections. In this review, we highlight the expression profile and role of the CXCL10/CXCR3 axis in the host defense against a variety of RNA and DNA viral infections. We also discuss the interactions among viruses and host cells that trigger CXCL10 expression, as well as the signaling cascades induced in CXCR3 positive cells.

IL-15 enhances CCR5-mediated migration of memory CD8+ T cells by upregulating CCR5 expression in the absence of TCR stimulation

During microbial infection, bystander CD8+ T cells that are not specific to infecting pathogens can be activated by interleukin (IL)-15. However, the tissue-homing properties of bystander-activated CD8+ T cells have not been elucidated. Here, we examine the effects of IL-15 on the expression of chemokine receptors on CD8+ T cells and their migration. IL-15 upregulates CCR5 in memory CD8+ T cells in the absence of T cell receptor (TCR) stimulation and enhances CCR5-dependent migration. IL-15-induced CCR5 upregulation is abrogated by TCR stimulation, indicating that CCR5 is upregulated in bystander-activated CD8+ T cells. Moreover, CCR5 signals increase proliferation and cytotoxic protein expression in IL-15-treated memory CD8+ T cells, although the increase has a small extent. CCR5 upregulation in bystander-activated CD8+ T cells is associated with severe liver injury in patients with acute hepatitis A. Altogether, the results indicate that CCR5 upregulation by IL-15 mediates the migration of bystander-activated CD8+ T cells.

Cytokine and chemokine profiles in episodes of persistent high-risk febrile neutropenia in children with cancer

BACKGROUND

In children with cancer and persistent high-risk febrile neutropenia (HRFN), cytokines/chemokines profiles can guide the differentiation of febrile neutropenia (FN) due to infections and episodes of unknown origin (FN-UO).

METHODS

A prospective, multicenter study in Santiago, Chile included patients ≤ 18 years with cancer and HRFN. Clinical and microbiological studies were performed according to validated protocols. Serum levels of 38 cytokines/chemokines were determined on day 4 of persistent HRFN. We performed comparisons between i) HRFN episodes with a detected etiological agent (FN-DEA) and FN-UO, and ii) bacterial versus viral infections. ROC curves were used to assess the discriminatory power of the analytes.

RESULTS

110 HRFN episodes were enrolled (median age 8 years, 53% female). Eighty-four patients were FN-DEA: 44 bacterial, 32 viral, and 8 fungal infections. Twenty-six cases were categorized as FN-UO. Both groups presented similar clinical and laboratory characteristics. Nineteen out of 38 analytes had higher concentrations in the FN-DEA versus FN-UO group. G-CSF, IL-6, and Flt-3L showed the highest discriminatory power to detect infection (AUC 0.763, 0.741, 0.701). Serum levels of G-CSF differentiated bacterial infections and IP-10 viral agents. A combination of G-CSF, IL-6, Flt-3L, and IP-10 showed an AUC of 0.839, 75% sensitivity, and 81% specificity.

CONCLUSION

A specific immune response is present on day four of persistent HRFN in children with cancer. We propose a combined measure of serum concentrations of G-CSF, IL-6, IP-10, and Flt-3L, in order to predict the presence of an infectious agent as compared to an episode of FN with unknown origin.

Circulating Cytokines and Coronavirus Disease: A Bi-Directional Mendelian Randomization Study

BACKGROUND

Immune system functioning is relevant to vulnerability to coronavirus disease (COVID-19). Cytokines are important to immunity. To further elucidate the role of the immune system in COVID-19, we used Mendelian randomization (MR) to assess comprehensively and bi-directionally the role of cytokines in COVID-19.

METHODS

We assessed primarily whether genetically different levels of 41 cytokines affected risk of any COVID-19 (laboratory confirmed, physician confirmed or self-reported, 36,590 cases, 1,668,938 controls), and conversely if genetic risk of liability to any COVID-19 affected these cytokines (n ≤ 8293) using the most recent genome-wide association studies. We obtained inverse variance weighting (IVW) estimates, conducted sensitivity analyses and used a Benjamini-Hochberg correction to account for multiple comparisons. We also assessed whether any findings were evident for hospitalized COVID-19 (hospitalized laboratory confirmed, 12,888 cases, 1,295,966 controls).

RESULTS

Macrophage inflammatory protein-1β (MIP1b; more commonly known as Chemokine (C-C motif) ligands 4 (CCL4) was inversely associated with COVID-19 [odds ratio (OR) 0.97 per SD, 95% confidence interval (CI) 0.96-0.99] but not after adjustment for multiple comparisons. This finding replicated for hospitalized COVID-19 (OR 0.93, 95% CI 0.89-0.98). Liability to any COVID-19 was nominally associated with several cytokines, such as granulocyte colony-stimulating factor (GCSF) and hepatocyte growth factor (HGF) but not after correction.

CONCLUSION

A crucial element of immune response to infection (CCL4) was related to COVID-19, whether it is a target of intervention to prevent COVID-19 warrants further investigation.

Prognostic, clinical, and therapeutic importance of RANTES-CCR5 axis in hepatitis A infection: A multiapproach study

Fulminant hepatic failure (FHF) is a lethal manifestation of hepatitis A virus (HAV) infection, whose underlying mechanisms are poorly understood. We aimed to evaluate the importance of the modulation of the RANTES-chemokine receptor type 5 (CCR5) signaling axis and its immunomodulatory effects in directing hepatitis A disease pathogenesis using an in silico, in vitro and patient cohort-based approach. In silico interaction studies were performed using computation approaches with suitable software. Differential expression of relevant cytokines and immune cell markers were studied using real-time quantitative reverse transcription PCR (qRT-PCR), enzyme-linked immunosorbent assay, and flow-cytometry-based methods. In the HepG2 cell line, we studied inflammatory responses and susceptibility to HAV infection following RANTES stimulation and antibody blockade of CCR5. The HAV-VP3 region exhibited high interaction in CCR5: HAV complexes. RANTES levels were significantly increased in FHF cases. Reduced monocyte and T-cell activation were observed in FHF cases. RANTES expression inversely correlated with viremia but positively correlated with proinflammatory responses. Hyper Th1-biased immune responses, marked by high interleukin (IL)-12/IL-10 ratio were observed in FHF cases, which were also characterized by upregulated tumor necrosis factor-alpha (TNF-α) expression and reduced interferon-gamma expression. In vitro, RANTES was protective against HAV infection but resulted in upregulated TNF-α expression. Although viral load increased upon the regulation of inflammatory responses by CCR5 blocking, it was still significantly lower compared to control HAV-infected cells. Our study suggests the importance of RANTES-CCR5 signaling and linked-immunomodulation in HAV disease pathogenesis, as well as highlights the utility of CCR5 antagonists as a risk-reduction strategy in FHF patients. Our findings, therefore, have important implications for the management of high-risk HAV infections.

Latent Cytomegalovirus-Driven Recruitment of Activated CD4+ T Cells Promotes Virus Reactivation

Human cytomegalovirus (HCMV) infection is not cleared by the initial immune response but persists for the lifetime of the host, in part due to its ability to establish a latent infection in cells of the myeloid lineage. HCMV has been shown to manipulate the secretion of cellular proteins during both lytic and latent infection; with changes caused by latent infection mainly investigated in CD34+ progenitor cells. Whilst CD34+ cells are generally bone marrow resident, their derivative CD14+ monocytes migrate to the periphery where they briefly circulate until extravasation into tissue sites. We have analyzed the effect of HCMV latent infection on the secretome of CD14+ monocytes, identifying an upregulation of both CCL8 and CXCL10 chemokines in the CD14+ latency-associated secretome. Unlike CD34+ cells, the CD14+ latency-associated secretome did not induce migration of resting immune cell subsets but did induce migration of activated NK and T cells expressing CXCR3 in a CXCL10 dependent manner. As reported in CD34+ latent infection, the CD14+ latency-associated secretome also suppressed the anti-viral activity of stimulated CD4+ T cells. Surprisingly, however, co-culture of activated autologous CD4+ T cells with latently infected monocytes resulted in reactivation of HCMV at levels comparable to those observed using M-CSF and IL-1β cytokines. We propose that these events represent a potential strategy to enable HCMV reactivation and local dissemination of the virus at peripheral tissue sites.

IP-10 and CXCR3 signaling inhibit Zika virus replication in human prostate cells

Our previous studies have shown that Zika virus (ZIKV) replicates in human prostate cells, suggesting that the prostate may serve as a long-term reservoir for virus transmission. Here, we demonstrated that the innate immune responses generated to three distinct ZIKV strains (all isolated from human serum) were significantly different and dependent on their passage history (in mosquito, monkey, or human cells). In addition, some of these phenotypic differences were reduced by a single additional cell culture passage, suggesting that viruses that have been passaged more than 3 times from the patient sample will no longer reflect natural phenotypes. Two of the ZIKV strains analyzed induced high levels of the IP-10 chemokine and IFNγ in human prostate epithelial and stromal mesenchymal stem cells. To further understand the importance of these innate responses on ZIKV replication, we measured the effects of IP-10 and its downstream receptor, CXCR3, on RNA and virus production in prostate cells. Treatment with IP-10, CXCR3 agonist, or CXCR3 antagonist significantly altered ZIKV viral gene expression, depending on their passage in cells of relevant hosts (mosquito or human). We detected differences in gene expression of two primary CXCR3 isoforms (CXCR3-A and CXCR3-B) on the two cell types, possibly explaining differences in viral output. Lastly, we examined the effects of IP-10, agonist, or antagonist on cell death and proliferation under physiologically relevant infection rates, and detected no significant differences. Although we did not measure protein expression directly, our results indicate that CXCR3 signaling may be a target for therapeutics, to ultimately stop sexual transmission of this virus.

EpCAM-high liver cancer stem cells resist natural killer cell-mediated cytotoxicity by upregulating CEACAM1

Background

Natural killer (NK) cells can recognize and kill cancer cells directly, but their activity can be attenuated by various inhibitory molecules expressed on the surface. The expression of epithelial cell adhesion molecule (EpCAM), a potential marker for cancer stem cells (CSCs), is known to be strongly associated with poor clinical outcomes in hepatocellular carcinoma (HCC). NK cells targeting CSCs may be a promising strategy for anti-tumor therapy, but little is known about how they respond to EpCAM^high CSCs in HCC.

Methods

EpCAM expression was assessed by immunohistochemistry in 280 human HCC tissues obtained from curative surgery. To investigate the functional activity of NK cells against liver CSCs, EpCAM^high and EpCAM^low Huh-7 cells were sorted by flow cytometry. The functional role of carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1), which is related to NK cells, was determined by in vitro co-culture of NK cells and hepatoma cells using Hepa1–6 mouse hepatoma cells, as well as in vivo experiments using C57/BL6 mice.

Results

The frequency of recurrence after curative surgery was higher in patients with positive EpCAM expression than in those with negative EpCAM expression. In subsequent analysis based on the anatomical location of EpCAM expression, patients with peritumoral EpCAM expression showed worse prognosis than those with pantumoral EpCAM expression. Co-culture experiments demonstrated that CEACAM1 was upregulated on the surface of EpCAM^high HCC cells, resulting in resistance to NK cell-mediated cytotoxicity. Inversely, silencing CEACAM1 restored cytotoxicity of NK cells against EpCAM^high Huh-7 cells. Moreover, neutralizing CEACAM1 on the NK cell surface enhanced killing of Huh-7 cells, suggesting that homophilic interaction of CEACAM1 is responsible for attenuated NK cell–mediated killing of CEACAM1^high cells. In mouse experiments with Hepa1–6 cells, EpCAM^high Hepa1–6 cells formed larger tumors and showed higher CEACAM1 expression after NK cell depletion. NK-mediated cytotoxicity was enhanced after blocking CEACAM1 expression using the anti-CEACAM1 antibody, thereby facilitating tumor regression. Moreover, CEACAM1 expression positively correlated with EpCAM expression in human HCC tissues, and serum CEACAM1 levels were also significantly higher in patients with EpCAM⁺ HCC.

Conclusion

Our data demonstrated that EpCAM^high liver CSCs resist NK cell–mediated cytotoxicity by upregulation of CEACAM1 expression.

Co-Occurrence of Hepatitis A Infection and Chronic Liver Disease

Hepatitis A virus (HAV) infection occasionally leads to a critical condition in patients with or without chronic liver diseases. Acute-on-chronic liver disease includes acute-on-chronic liver failure (ACLF) and non-ACLF. In this review, we searched the literature concerning the association between HAV infection and chronic liver diseases in PubMed. Chronic liver diseases, such as metabolic associated fatty liver disease and alcoholic liver disease, coinfection with other viruses, and host genetic factors may be associated with severe hepatitis A. It is important to understand these conditions and mechanisms. There may be no etiological correlation between liver failure and HAV infection, but there is an association between the level of chronic liver damage and the severity of acute-on-chronic liver disease. While the application of an HAV vaccination is important for preventing HAV infection, the development of antivirals against HAV may be important for preventing the development of ACLF with HAV infection as an acute insult. The latter is all the more urgent given that the lives of patients with HAV infection and a chronic liver disease of another etiology may be at immediate risk.

Evidence of virus-responsive pathways in response to poly I: C challenge in a muscle cell line derived from large yellow croaker Larimichthys crocea

In this study, a new continuous muscle cell line, LYCMS (large yellow croaker muscle cell line), derived from the muscle tissue of larva of large yellow croaker (Larimichthys crocea) was developed with modified DMEM/F12 medium at 27 °C. The muscle cell line could be passaged at different ratios for different growth rates. Karyotype analysis showed that a large proportion of LYCMS cells had 48 chromosomes. The proliferation of LYCMS cell line could be affected by mammalian growth factors such as human basic fibroblast growth factor (b-FGF), epidermal growth factor (EGF), and hepatocyte growth factor (HGF). GFP expression experiments indicated that the LYCMS cell line could be used for exogenous genes' expression. Different virus response-related genes tested in this study showed diverse change types in expression before and after (0-24 h) polycytidylic acid (poly I: C) challenge of LYCMS cells. This is the first study of virus response signaling pathways of large yellow croaker based on the muscle cell line. The results showed that compared with the in vivo experiments, the use of the LYCMS cell line for immune research is more convenient, efficient, and rapid. By using this model, we demonstrated that MDA5-IPS1-TRAF6-NFκB-cytokines, MDA5-IPS1-TRAF3-IRF3-interferon or TLR22-TRIF-IRF3-interferon, TLR8-MyD88-NFκB-cytokines, and TLR3-TRIF-IRF3-interferon pathways were able to response to poly I: C challenge in the muscle cell line of large yellow croaker.

Unique Roles for Streptococcus pneumoniae Phosphodiesterase 2 in Cyclic di-AMP Catabolism and Macrophage Responses

Cyclic di-AMP (c-di-AMP) is an important signaling molecule for pneumococci, and as a uniquely prokaryotic product it can be recognized by mammalian cells as a danger signal that triggers innate immunity. Roles of c-di-AMP in directing host responses during pneumococcal infection are only beginning to be defined. We hypothesized that pneumococci with defective c-di-AMP catabolism due to phosphodiesterase deletions could illuminate roles of c-di-AMP in mediating host responses to pneumococcal infection. Pneumococci deficient in phosphodiesterase 2 (Pde2) stimulated a rapid induction of interferon β (IFNβ) expression that was exaggerated in comparison to that induced by wild type (WT) bacteria or bacteria deficient in phosphodiesterase 1. This IFNβ burst was elicited in mouse and human macrophage-like cell lines as well as in primary alveolar macrophages collected from mice with pneumococcal pneumonia. Macrophage hyperactivation by Pde2-deficient pneumococci led to rapid cell death. STING and cGAS were essential for the excessive IFNβ induction, which also required phagocytosis of bacteria and triggered the phosphorylation of IRF3 and IRF7 transcription factors. The select effects of Pde2 deletion were products of a unique role of this enzyme in c-di-AMP catabolism when pneumococci were grown on solid substrate conditions designed to enhance virulence. Because pneumococci with elevated c-di-AMP drive aberrant innate immune responses from macrophages involving hyperactivation of STING, excessive IFNβ expression, and rapid cytotoxicity, we surmise that c-di-AMP is pivotal for directing innate immunity and host-pathogen interactions during pneumococcal pneumonia.

Rotavirus Reprograms Multiple Interferon Receptors and Restricts Their Intestinal Antiviral and Inflammatory Functions

Rotaviruses (RV) cause acute severe diarrhea in the absence of substantial intestinal inflammation. They are also highly infectious in their homologous host species. The replication capacity of RV in the small bowel is substantially due to its ability to inhibit different types of interferons (IFNs). Here, we found that during RV infection in vitro, both virus-infected and uninfected bystander cells resist STAT1 phosphorylation and interferon regulatory factor 7 (IRF7) induction in response to exogenous interferon (IFN). Functionally, cellular transcription in response to stimulation with IFN, but not intracellular double-stranded RNA (dsRNA), was inhibited by RV. Further, IFNAR1 stimulation during RV infection significantly repressed a set of virus-induced transcripts. Regulation of IFN signaling in vivo was studied in suckling mice using the highly infectious murine EW RV strain. Kinetic studies indicated that sustained EW RV replication and IFN induction in the small intestine are accompanied by significant decreases in IFN-stimulated transcripts. Lipopolysaccharide (LPS)-mediated intestinal damage, driven by STAT1-induced inflammation, was also prevented in EW RV-infected mice. Remarkably, by ectopically stimulating either IFNAR1 or IFNGR1 in EW RV-infected mice, we could eliminate several intestinal antiviral and inflammatory transcriptional responses to RV. In contrast to infection with homologous RV, infection with a STAT1-sensitive heterologous RV strain induced IFN-stimulated transcripts, inflammatory cytokines, and intestinal expression of STAT1-pY701. Finally, RV strain-specific STAT1 regulation also likely determines the intestinal activation of multiple caspases. The simian RRV strain, but not murine EW RV, uniquely triggers the cleavage of both extrinsic and intrinsic caspases (caspases 8, 9, and 3) in a STAT1-mediated manner. Collectively, our findings reveal efficient reprograming of multiple IFN receptors toward a negative-feedback mode of signaling, accompanied by suppression of IFN-mediated antiviral, apoptotic, and inflammatory functions, during natural RV intestinal infection.IMPORTANCE Rotavirus is a highly infectious pathogen that causes severe diarrhea. Replication of RV in the small intestine is restricted to homologous host species, and host range restriction is substantially determined by the interferon response. In this study, we demonstrate that during infection, RV bystander cells resist exogenous IFN-mediated STAT1 signaling and transcription. In a suckling mouse model, ectopically stimulating different intestinal interferon receptors during RV infection eliminates several innate and inflammatory antiviral responses. Different intestinal inflammatory cytokines were also suppressed by homologous RV, as was intestinal damage in response to endotoxin. The ability of RV to suppress IFN-mediated receptors likely impacts intestinal cell homeostasis, as the cleavage of multiple intestinal caspases during RV infection is mediated by the IFN-STAT1 signaling pathway. Together, our results provide a mechanism underlying both the remarkable interferon resistance of homologous RV and its ability to prevent substantial inflammatory damage to the small bowel.

Innate Immune Response to Influenza Virus at Single-Cell Resolution in Human Epithelial Cells Revealed Paracrine Induction of Interferon Lambda 1

Early interactions of influenza A virus (IAV) with respiratory epithelium might determine the outcome of infection. The study of global cellular innate immune responses often masks multiple aspects of the mechanisms by which populations of cells work as organized and heterogeneous systems to defeat virus infection, and how the virus counteracts these systems. In this study, we experimentally dissected the dynamics of IAV and human epithelial respiratory cell interaction during early infection at the single-cell level. We found that the number of viruses infecting a cell (multiplicity of infection [MOI]) influences the magnitude of virus antagonism of the host innate antiviral response. Infections performed at high MOIs resulted in increased viral gene expression per cell and stronger antagonist effect than infections at low MOIs. In addition, single-cell patterns of expression of interferons (IFN) and IFN-stimulated genes (ISGs) provided important insights into the contributions of the infected and bystander cells to the innate immune responses during infection. Specifically, the expression of multiple ISGs was lower in infected than in bystander cells. In contrast with other IFNs, IFN lambda 1 (IFNL1) showed a widespread pattern of expression, suggesting a different cell-to-cell propagation mechanism more reliant on paracrine signaling. Finally, we measured the dynamics of the antiviral response in primary human epithelial cells, which highlighted the importance of early innate immune responses at inhibiting virus spread.IMPORTANCE Influenza A virus (IAV) is a respiratory pathogen of high importance to public health. Annual epidemics of seasonal IAV infections in humans are a significant public health and economic burden. IAV also causes sporadic pandemics, which can have devastating effects. The main target cells for IAV replication are epithelial cells in the respiratory epithelium. The cellular innate immune responses induced in these cells upon infection are critical for defense against the virus, and therefore, it is important to understand the complex interactions between the virus and the host cells. In this study, we investigated the innate immune response to IAV in the respiratory epithelium at the single-cell level, providing a better understanding on how a population of epithelial cells functions as a complex system to orchestrate the response to virus infection and how the virus counteracts this system.

Stem Cell-Derived Hepatocyte-Like Cells as Model for Viral Hepatitis Research

Viral hepatitis, the leading cause of liver diseases worldwide, is induced upon infection with hepatotropic viruses, including hepatitis A, B, C, D, and E virus. Due to their obligate intracellular lifestyles, culture systems for efficient viral replication are vital. Although basic and translational research on viral hepatitis has been performed for many years, conventional hepatocellular culture systems are not optimal. These studies have greatly benefited from recent efforts on improving cell culture models for virus replication and infection studies. Here we summarize the use of human stem cell-derived hepatocyte-like cells for hepatotropic virus infection studies, including the dissection of virus-host interactions and virus-induced pathogenesis as well as the identification and validation of novel antiviral agents.

Early Cutaneous Leishmaniasis Patients Infected With Leishmania braziliensis Express Increased Inflammatory Responses After Antimony Therapy

Background

Early cutaneous leishmaniasis (ECL) is characterized by a nonulcerated papular lesion and illness duration less than 30 days. Approximately 4 weeks later, the cutaneous leishmaniasis (CL) ulcers appear. We were surprised to find that failure after antimony therapy (Sb5) is higher in ECL than CL. We hypothesize that the inflammatory response in ECL patients may increase during Sb5 therapy, which leads to treatment failure.

Methods

A cohort of 44 ECL patients infected by Leishmania braziliensis was established to evaluate the response to Sb5 and to compare immunologic responses in ECL patients with CL and healthy subjects.

Results

A hierarchical clustering based on cytokine levels showed a weak positive correlation between proinflammatory cytokine levels and those patients that failed Sb5 treatment. Although Sb5 therapy decreased interferon-γ and tumor necrosis factor levels in CL patients, we were surprised to find that an increase in these cytokines was observed in ECL patients. Moreover, interleukin (IL)-10 was less able to down-modulate immune responses in ECL.

Conclusions

The enhanced production of proinflammatory cytokines, due in part to the decreased ability of IL-10 to down-modulate immune response during therapy in ECL, promotes the development and persistence of leishmania ulcer despite antimony therapy.

Innate Immunity to Enteric Hepatitis Viruses

Although hepatitis A virus (HAV) and hepatitis E virus (HEV) are both positive-strand RNA viruses that replicate in the cytoplasm of hepatocytes, there are important differences in the ways they induce and counteract host innate immune responses. HAV is remarkably stealthy because of its ability to evade and disrupt innate signaling pathways that lead to interferon production. In contrast, HEV does not block interferon production. Instead, it persists in the presence of an interferon response. These differences may provide insight into HEV persistence in immunocompromised patients, an emerging health problem in developed countries.

Natural History, Clinical Manifestations, and Pathogenesis of Hepatitis A

Hepatitis A virus (HAV) is transmitted by the fecal-oral route and is a major cause of acute viral hepatitis. The clinical manifestations of HAV infection range from asymptomatic infection to acute liver failure (ALF), but do not include progression to chronic hepatitis. Risk factors for severe acute hepatitis A are older age (>40 years) and preexisting liver disease. Some patients may show atypical clinical features such as relapsing hepatitis, prolonged cholestasis, or extrahepatic manifestations. Almost all hepatitis A patients spontaneously recover with supportive care. However, in the case of ALF (<1%), intensive care and urgent decision on liver transplantation are required. Liver injury during hepatitis A is not directly caused by HAV but is known to be caused by immune-mediated mechanisms. In this review, the natural history and clinical manifestations of hepatitis A are described. In addition, mechanisms of immunopathogenesis in hepatitis A are discussed.

Interferon-free treatment for hepatitis C virus infection induces normalization of extrahepatic type I interferon signaling

Background/Aims

Hepatitis C virus (HCV) replicates in the peripheral blood mononuclear cells (PBMCs), leading to the production of type I interferons (IFNs). It is well known that the gene expression profile of PBMC is similar to that of the liver. The present study explored the dynamic gene expression profile of PBMCs collected from HCV-infected patients undergoing direct-acting antiviral (DAA) therapy.

Methods

A prospective cohort comprising 27 patients under DAA therapy was formed. Expression level of IFN-β and its downstream interferon-stimulated genes (ISGs) was measured in PBMCs before and after DAA treatment. Furthermore, immunoblotting was performed to identify the signaling molecules involved in the expression of ISGs.

Results

The pretreatment expression level of interferon-induced protein 44 (IFI44) and C-X-C motif chemokine ligand 10 (CXCL10) correlated with the pretreatment expression level of IFN-β. After DAA treatment, a significant decrease in the expression levels of IFN-β, IFI44, and CXCL10 was observed in the PBMCs. Furthermore, the pretreatment expression level of IFN-β and ISGs correlated with the level of signal transducer and activator of transcription 1 (STAT1) phosphorylation, and DAA treatment abrogated STAT1 phosphorylation.

Conclusions

Pretreatment activation of IFN-β response is rapidly normalized after DAA treatment. The present study suggests that the decreased type I IFN response by the clearance of HCV might contribute to DAA-induced alleviation of extrahepatic manifestation of chronic HCV infection.