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The expression and processing of the Hepatitis C virus core protein (HCcAg) were analyzed in the methylotrophic yeast Pichia pastoris. Two proteins with 21 (p21) and 23 kDa (p23) were detected in immunoblot with a serum from a chronic carrier patient, as the major products for HCcAg. Both proteins, p21 and p23, produced by proteolytic processing in P. partoris, share the same N-terminal region and reacted with a monoclonal antibody towards the first 35 amino acids of HCcAg. The proteolytic processing of the recombinant polypeptide, having the HCcAg and the first 148 aa of E1 protein, was also confirmed by immunoblot analysis using mAbs with HCcAg and E1 specificities, respectively. The 32 kDa glycosilated E1 protein was then immuno-identified, as well as the processed HCcAg. These data demonstrated the usefulness of P. pastoris, as expression system, to study the processing of HCV structural proteins.

Immunological response against envelope protein E1 is very important in natural hepatitis C virus (HCV) infection, although it is insufficient to clear the viraemia. The HCV genomic region encoding the first 149 amino acids of the envelope E1 protein (E1(340), amino acids 192-340) was expressed in Escherichia coli (to a level of 30% of the whole cellular proteins) and purified to 85%. We measured the immune response in rabbits and mice as well as the reactivity against 37 human sera raised against the whole recombinant protein and E1-encoding peptides. From this, 51.1% of human sera were found to react with E1(340). High-level antibodies against E1(340) were obtained in rabbits and mice when immunized. These antibodies had a similar peptide-recognition pattern to that described previously for human sera. The most reactive region was located at the N-terminus of the E1 protein. Cellular immunity in mice was evaluated by delayed-type hypersensitivity assay. It revealed the induction of a CD4+ T-cell-mediated response by this protein. This E1(340) protein and the animal-derived anti-E1 sera are immunological tools that could aid in the monitoring and development of anti-HCV therapies.

Herpes simplex encephalitis is a rare manifestation of herpes simplex virus-1 infection. Mutations in genes of the toll-like receptor 3-interferon pathway have been shown to predispose to childhood herpes simplex encephalitis, including UNC93B1, TLR3, TRIF, TRAF3 and TBK1. We investigated herpes simplex encephalitis patients with impaired toll-like receptor 3 signaling for whom the involvement of the known genetic etiologies have been excluded. Exome sequencing was used to identify other mutations underlying herpes simplex encephalitis, paying particular attention to the toll-like receptor 3-interferon pathway by employing a candidate gene based ‘connectome’ approach. One patient in particular carried a novel heterozygous missense mutation in a known gene in the nuclear factor-κB / toll-like receptor 3 pathway. The patient’s cells showed a decrease in interferon regulatory factor-3 dimerization and reduced nuclear translocation of nuclear factor-κB consistent with the lack of type I interferon and IL6 production following toll-like receptor 3 stimulation. The patients’ cells were also more susceptible upon viral infections. Further characterization of the mutation and its impact on type I interferon signaling in the context of herpes simplex virus-1 infection will provide a better understanding of the etiology of childhood herpes simplex encephalitis.

Fulminant viral hepatitis (FVH) is a devastating and unexplained condition that strikes otherwise healthy individuals during primary infection with common liver-tropic viruses. We report a child who died of FVH upon infection with hepatitis A virus (HAV) at age 11 yr and who was homozygous for a private 40-nucleotide deletion in IL18BP, which encodes the IL-18 binding protein (IL-18BP). This mutation is loss-of-function, unlike the variants found in a homozygous state in public databases. We show that human IL-18 and IL-18BP are both secreted mostly by hepatocytes and macrophages in the liver. Moreover, in the absence of IL-18BP, excessive NK cell activation by IL-18 results in uncontrolled killing of human hepatocytes in vitro. Inherited human IL-18BP deficiency thus underlies fulminant HAV hepatitis by unleashing IL-18. These findings provide proof-of-principle that FVH can be caused by single-gene inborn errors that selectively disrupt liver-specific immunity. They also show that human IL-18 is toxic to the liver and that IL-18BP is its antidote.

The molecular basis of interindividual clinical variability upon infection withStaphylococcus aureusis unclear. We describe patients with haploinsufficiency for the linear deubiquitinase OTULIN, encoded by a gene on chromosome 5p. Patients suffer from episodes of life-threatening necrosis, typically triggered byS. aureusinfection. The disorder is phenocopied in patients with the 5p− (Cri-du-Chat) chromosomal deletion syndrome. OTULIN haploinsufficiency causes an accumulation of linear ubiquitin in dermal fibroblasts, but tumor necrosis factor receptor–mediated nuclear factor κB signaling remains intact. Blood leukocyte subsets are unaffected. The OTULIN-dependent accumulation of caveolin-1 in dermal fibroblasts, but not leukocytes, facilitates the cytotoxic damage inflicted by the staphylococcal virulence factor α-toxin. Naturally elicited antibodies against α-toxin contribute to incomplete clinical penetrance. Human OTULIN haploinsufficiency underlies life-threatening staphylococcal disease by disrupting cell-intrinsic immunity to α-toxin in nonleukocytic cells.

Introduction Herpes simplex encephalitis (HSE) is the most common sporadic viral encephalitis in children in Western countries. Only early administration of antiviral drugs can improve the mortality rate, which goes up to 70% without treatment. In different pediatric studies on children with HSE treated by acyclovir about 50% of patients recovered fully, whereas about 40% stayed with moderate to severe neurological impairment. Recent studies reported that specific genetic immunodeficiencies lead to increased HSE susceptibility and that secondary immune-mediated processes can modify disease evolution. Some of these immunodeficiencies such as defects in Toll-like receptor signalling can be detected by cheap and fast tests.