Defective RNA sensing by RIG-I in severe influenza virus infection.

Influenza virus infection causes worldwide seasonal epidemics. Although influenza is usually a mild disease, a minority of patients experience very severe fulminating disease courses. Previous studies have demonstrated a role for type I interferon (IFN) in anti-viral responses during influenza. So far, however, IFN regulatory factor (IRF)7 deficiency is the only genetic cause of severe influenza described in humans. In this study we present a patient with severe influenza A virus (IAV) H1N1 infection during the 2009 swine flu pandemic. By whole exome sequencing we identified two variants, p.R71H and p.P885S, located in the caspase activation and recruitment domain (CARD) and RNA binding domains, respectively, of DExD/H-box helicase 58 (DDX58) encoding the RNA sensor retinoic acid inducible gene 1 (RIG-I). These variants significantly impair the signalling activity of RIG-I. Similarly, patient cells demonstrate decreased antiviral responses to RIG-I ligands as well as increased proinflammatory responses to IAV, suggesting dysregulation of the innate immune response with increased immunopathology. We suggest that these RIG-I variants may have contributed to severe influenza in this patient and advocate that RIG-I variants should be sought in future studies of genetic factors influencing single-stranded RNA virus infections.

A conserved sugar bridge connected to the WSXWS motif has an important role for transport of IL-21R to the plasma membrane.

Interleukin-21 (IL-21) is a class I cytokine that belongs to the γc-subfamily of cytokines and regulates immune responses. It signals through a heterodimeric receptor complex composed of the IL-21R1 and γc-receptor chains. A characteristic feature of class I cytokine receptors is the presence of a consensus motif WSXWS (WS motif) in the membrane proximal fibronectin type III domain (FNIII) of these receptors. We recently described the structure of the IL-21R:IL-21 complex and showed that the first tryptophan of the WS motif of IL-21R is mannosylated and involved in formation of a sugar bridge that connects the two FNIII domains of the receptor. Furthermore, a mutation within the WS motif of IL-21R was recently shown to cause a novel kind of primary immunodeficiency syndrome (PID). Here, we report the structure of IL-21R alone, which shows that the sugar bridge forms independently of whether IL-21R binds IL-21 or not, and we furthermore investigate the role of this bridge in the export of IL-21R and γC to the plasma membrane. Thus, we provide a molecular explanation for how mutations in the WS motif may cause PIDs.

Transcriptome analysis reveals a classical interferon signature induced by IFNλ4 in human primary cells.

The IFNL4 gene is negatively associated with spontaneous and treatment-induced clearance of hepatitis C virus infection. The activity of IFNλ4 has an important causal role in the pathogenesis, but the molecular details are not fully understood. One possible reason for the detrimental effect of IFNλ4 could be a tissue-specific regulation of an unknown subset of genes. To address both tissue and subtype specificity in the interferon response, we treated primary human hepatocytes and airway epithelial cells with IFNα, IFNλ3 or IFNλ4 and assessed interferon mediated gene regulation using transcriptome sequencing. Our data show a surprisingly similar response to all three subtypes of interferon. We also addressed the tissue specificity of the response, and identified a subset of tissue-specific genes. However, the interferon response is robust in both tissues with the majority of the identified genes being regulated in hepatocytes as well as airway epithelial cells. Thus we provide an in-depth analysis of the liver interferon response seen over an array of interferon subtypes and compare it to the response in the lung epithelium.

Human interferon-lambda3 is a potent member of the type III interferon family.

Type III interferon (IFN) or IFN-lambda is a recently discovered family of IFNs that signal through the same downstream transcription factors as type I IFN but use a separate receptor complex composed of the IL-10R2 and the unique IFN-lambdaR1 receptor chains. We have established a simple and efficient expression system to produce highly pure and active IFN-lambda of the three human IFN-lambda isoforms (IFN-lambda1, -lambda2 and -lambda3) and used this to compare the biological activity of the different IFN-lambda subtypes. Surprisingly, we found IFN-lambda3 to possess the highest specific activity of the human IFN-lambda subtypes, exhibiting a twofold higher activity than IFN-lambda1 and a 16-fold higher activity than IFN-lambda2. Furthermore, in comparison with the commercially available preparations of IFN-lambda1 and -lambda2, we found our IFN-lambda preparation to be superior in activity.