Locking down access to the brain Inflammatory bowel disease is best known for intestinal symptoms but can also cause a variety of extraintestinal manifestations in other organs. It can also be associated with cognitive and psychiatric effects, including anxiety and depression. Using mouse models of intestinal inflammation, Carloni et al . uncovered a potential pathogenic link between these aspects of inflammatory bowel disease. The inflammatory process causes the gut vascular barrier to become more permeable, resulting in the spread of inflammation beyond the intestine, while the vascular barrier in the choroid plexus shuts down, helping protect the brain from inflammation but also potentially impairing communication between organs and impairing some brain functions. —YN

Background & Aims Liver sinusoidal endothelial cells (LSECs) make up a large proportion of the non-parenchymal cells in the liver. LSECs are involved in induction of immune tolerance, but little is known about their functions during hepatitis C virus (HCV) infection. Methods Primary human LSECs (HLSECs) and immortalized liver endothelial cells (TMNK-1) were exposed to various forms of HCV, including full-length transmitted/founder virus, sucrose-purified Japanese Fulminant Hepatitis-1 (JFH-1), a virus encoding a luciferase reporter, and the HCV-specific pathogen-associated molecular pattern molecules. Cells were analyzed by confocal immunofluorescence, immunohistochemical, and PCR assays. Results HLSECs internalized HCV, independent of cell–cell contacts; HCV RNA was translated but not replicated. Through pattern recognition receptors (TLR7 and retinoic acid inducible gene 1), HCV RNA induced consistent and broad transcription of multiple interferons (IFNs); supernatants from primary HLSECs transfected with HCV-specific pathogen-associated molecular pattern molecules increased induction of IFNs and IFN-stimulated genes in HLSECs. Recombinant type I and type III IFNs strongly up-regulated HLSEC transcription of interferon λ 3 (IFNL3) and viperin (RSAD2), which inhibit replication of HCV. Compared to CD8+ T cells, HLSECs suppressed HCV replication within Huh7.5.1 cells, also inducing IFN-stimulated genes in co-culture. Conditioned media from IFN-stimulated HLSECs induced expression of antiviral genes by uninfected primary human hepatocytes. Exosomes, derived from HLSECs following stimulation with either type I or type III IFNs, controlled HCV replication in a dose-dependent manner. Conclusions Cultured HLSECs produce factors that mediate immunity against HCV. HLSECs induce self-amplifying IFN-mediated responses and release of exosomes with antiviral activity.

The inherent sequence diversity of the hepatitis C virus (HCV) represents a major hurdle for the adaptive immune system to control viral replication. Mutational escape within targeted CD8 epitopes during acute HCV infection has been well documented and is one possible mechanism for T-cell failure. HLA-B*08 was recently identified as one HLA class I allele associated with spontaneous clearance of HCV replication. Selection of escape mutations in the immunodominant HLA-B*08-restricted epitope HSKKKCDEL 1395-1403 was observed during acute infection. However, little is known about the impact of escape mutations in this epitope on viral replication capacity. Their previously reported reversion back toward the consensus residue in patients who do not possess the B*08 allele suggests that the consensus sequence in this epitope is advantageous for viral replication in the absence of immune pressure. The aim of this study was to determine the impact of mutational escape from this immunodominant epitope on viral replication. We analyzed it with a patient cohort with chronic HCV genotype 1b infection and in a single-source outbreak (genotype 1b). Sequence changes in this highly conserved region are rare and selected almost exclusively in the presence of the HLA-B*08 allele. When tested in the subgenomic replicon (Con1), the observed mutations reduce viral replication compared with the prototype sequence. The results provide direct evidence that escape mutations in this epitope are associated with fitness costs and that the antiviral effect of HLA-B*08-restricted T cells is sufficiently strong to force the virus to adopt a relatively unfavorable sequence.

Plasmacytoid Dendritic Cells (pDCs) represent a key immune cell in the defense against viruses. Through pattern recognition receptors (PRRs), these cells detect viral pathogen associated molecular patterns (PAMPs) and initiate an Interferon (IFN) response. pDCs produce the antiviral IFNs including the well-studied Type I and the more recently described Type III. Recent genome wide association studies (GWAS) have implicated Type III IFNs in HCV clearance. We examined the IFN response induced in a pDC cell line and ex vivo human pDCs by a region of the HCV genome referred to as the HCV PAMP. This RNA has been shown previously to be immunogenic in hepatocytes, whereas the conserved X-region RNA is not. We show that in response to the HCV PAMP, pDC-GEN2.2 cells upregulate and secrete Type III (in addition to Type I) IFNs and upregulate PRR genes and proteins. We also demonstrate that the recognition of this RNA is dependent on RIG-I-like Receptors (RLRs) and Toll-like Receptors (TLRs), challenging the dogma that RLRs are dispensable in pDCs. The IFNs produced by these cells in response to the HCV PAMP also control HCV replication in vitro. These data are recapitulated in ex vivo pDCs isolated from healthy donors. Together, our data shows that pDCs respond robustly to HCV RNA to make Type III Interferons that control viral replication. This may represent a novel therapeutic strategy for the treatment of HCV.

Background & Aims The pro-inflammatory chemokine CXCL10 is induced by HCV (hepatitis C virus) infection in vitro and in vivo, and is associated with outcome of IFN (interferon)-based therapy. We studied how hepatocyte sensing of early HCV infection via TLR3 (Toll-like receptor 3) and RIG-I (retinoic acid inducible gene I) led to expression of CXCL10. Methods CXCL10, type I IFN, and type III IFN mRNAs and proteins were measured in PHH (primary human hepatocytes) and hepatocyte lines harboring functional or non-functional TLR3 and RIG-I pathways following HCV infection or exposure to receptor-specific stimuli. Results Huh7 human hepatoma cells expressing both TLR3 and RIG-I produced maximal CXCL10 during early HCV infection. Neutralization of type I and type III IFNs had no impact on virus-induced CXCL10 expression in TLR3+/RIG-I+ Huh7 cells, but reduced CXCL10 expression in PHH. PHH cultures were positive for monocyte, macrophage, and dendritic cell mRNAs. Immunodepletion of non-parenchymal cells (NPCs) eliminated marker expression in PHH cultures, which then showed no IFN requirement for CXCL10 induction during HCV infection. Immunofluorescence studies also revealed a positive correlation between intracellular HCV Core and CXCL10 protein expression (r2=0.88, p=<0.001). Conclusions While CXCL10 induction in hepatocytes during the initial phase of HCV infection is independent of hepatocyte-derived type I and type III IFNs, NPC-derived IFNs contribute to CXCL10 induction during HCV infection in PHH cultures.