IFN-functionally resembles type I IFN, inducing antiviral protection in vitro (10,23,27) as well as in vivo (1). Activation of the IFN-receptor leads to the phosphorylation of STAT1, STAT2, and STAT3 and the formation of the interferon-stimulated gene factor 3 (ISGF3) transcription factor (10) and to the induction of typical IFN-induced genes like the OAS and MxA genes. IFN-can reduce cell growth in vitro and possesses antitumor activity in several rodent models (11,25). However, a number of cytokines with very different biological effects activate STAT transcription factors, and pronounced functional differences between type I and type III IFNs exist. The in vivo antiviral activity of IFN-against herpes simplex virus 2 (HSV-2) has been shown to be comparable to that of IFN-␣ in a systemic model. However, a model for the clinically relevant vaginal HSV-2 infection revealed an antiviral activity of IFN-that surpassed that of IFN-␣ (1).The biological effect of the cytokine-receptor system is determined primarily by three factors: the expression profile of the cytokine itself, the expression profile of the receptor, and the set of target genes for regulation. We decided to start our investigation of the function of the IFN-system by asking which genes are regulated by IFN-. A gene array experiment covering the whole human genome revealed that all IFN--induced genes were also induced by type I IFN. Thus, no genes

Because the availability of fish genomic data, the number of reported sequences for fish type II helical cytokines is rapidly growing, featuring different IFNs including virus-induced IFNs (IFNφ) and IFN-γ, and IL-10 with its related cytokines (IL-20, IL-22, and IL-26). Many candidate receptors exist for these cytokines and various authors have postulated which receptor chain would be involved in which functional receptor in fish. To date, only the receptor for zebrafish IFNφ1 has been identified functionally. Three genes encoding virus-induced IFNφs have been reported in zebrafish. In addition to these genes clustered on chromosome 3, we have identified a fourth IFNφ gene on chromosome 12. All these genes possess the intron-exon organization of mammalian λ IFNs. In the zebrafish larva, all induce the expression of reporter antiviral genes; protection in a viral challenge assay was observed for IFNφ1 and IFNφ2. Using a combination of gain- and loss-of-function experiments, we also show that all zebrafish IFNφs do not bind to the same receptor. Two subgroups of fish virus-induced IFNs have been defined based on conserved cysteines, and we find that this subdivision correlates with receptor usage. Both receptor complexes include a common short chain receptor (CRFB5) and a specific long chain receptor (CRFB1 or CRFB2).

The recent emergence of a novel human coronavirus (HCoV-EMC) in the Middle East raised considerable concerns, as it is associated with severe acute pneumonia, renal failure, and fatal outcome and thus resembles the clinical presentation of severe acute respiratory syndrome (SARS) observed in 2002 and 2003. Like SARS-CoV, HCoV-EMC is of zoonotic origin and closely related to bat coronaviruses. The human airway epithelium (HAE) represents the entry point and primary target tissue for respiratory viruses and is highly relevant for assessing the zoonotic potential of emerging respiratory viruses, such as HCoV-EMC. Here, we show that pseudostratified HAE cultures derived from different donors are highly permissive to HCoV-EMC infection, and by using reverse transcription (RT)-PCR and RNAseq data, we experimentally determined the identity of seven HCoV-EMC subgenomic mRNAs. Although the HAE cells were readily responsive to type I and type III interferon (IFN), we observed neither a pronounced inflammatory cytokine nor any detectable IFN responses following HCoV-EMC, SARS-CoV, or HCoV-229E infection, suggesting that innate immune evasion mechanisms and putative IFN antagonists of HCoV-EMC are operational in the new host. Importantly, however, we demonstrate that both type I and type III IFN can efficiently reduce HCoV-EMC replication in HAE cultures, providing a possible treatment option in cases of suspected HCoV-EMC infection.

The IFNL4 gene is a recently discovered type III interferon, which in a significant fraction of the human population harbours a frameshift mutation abolishing the IFNk4 ORF. The expression of IFNk4 is correlated with both poor spontaneous clearance of hepatitis C virus (HCV) and poor response to treatment with type I interferon. Here, we show that the IFNL4 gene encodes an active type III interferon, named IFNk4, which signals through the IFNkR1 and IL-10R2 receptor chains. Recombinant IFNk4 is antiviral against both HCV and coronaviruses at levels comparable to IFNk3. However, the secretion of IFNk4 is impaired compared to that of IFNk3, and this impairment is not due to a weak signal peptide, which was previously believed. We found that IFNk4 gets N-linked glycosylated and that this glycosylation is required for secretion. Nevertheless, this glycosylation is not required for activity. Together, these findings result in the paradox that IFNk4 is strongly antiviral but a disadvantage during HCV infection.

Interferon-(IFN-) is an antiviral cytokine that signals through a distinct receptor complex, composed of the IFN-R1and interleukin-10R2 (IL-10R2) receptor chains. We have determined the crystal structure of human IFN-3 and characterized the interaction with its receptor complex through structurebased site-directed mutagenesis. The ability of IFN-3 mutants to signal was determined by measuring the antiviral activity and induced STAT2 phosphorylation. In conclusion, our data show that, although IFN-is functionally an interferon, it is clearly structurally related to members of the IL-10 family. In particular, we found an interesting similarity between IFN-and IL-22, and we suggest that IFN-and IL-22 possess parallel functions, protecting epithelial tissue against viral and bacterial infections, respectively.In 2003, a novel family of cytokines was discovered simultaneously by two independent research teams (1, 2). Initially, the two research teams named these novel cytokines either interferon-(IFN-) 2 1, 2, and 3 or interleukin-29 (IL-29), -28A, or -28B. Throughout this report we will use the IFN-designation or type III IFN, when referring to all tree subtypes as a group. Like type I IFN, type III IFN induces antiviral activity both in vitro (3, 4) and in vivo (5). Thus the two types of IFN seem to have similar biological effects at a cellular level. IFN-uses a distinct receptor complex consisting of a unique subunit, named IFN-R1, as well as the IL-10R2 subunit. The similar biological effects caused by type I and III IFN can be explained by activation of a highly overlapping set of transcription factors. In particular, both types of IFN lead to phosphorylation of signal transducers and activators of transcription (STAT) 1, 2, and 3, followed by assembly of the interferon-stimulated gene factor 3 transcription factor and thus target the same population of genes for induction (6 -8).The expression of type III IFN appears to be induced by the same stimuli and depend upon the same signaling pathways as type I IFN. For example, type III IFN has been shown to be induced by a variety of viruses such as influenza A virus, herpes viruses, and Sendai virus as well as lipopolysaccharides or double-stranded RNA (9 -11). However, the contribution of different cell populations to the production of IFN-is not yet clear. An important difference between the type I and III IFN systems is the expression pattern of their receptors. Whereas most cell types express the type I IFN receptor complex and the IL-10R2 component of the IFN-receptor, the expression of the IFN-R1 receptor subunit is highly restricted (12, 13). The exact expression pattern of the IFN-R1 is not yet fully established, but it is clear that cells of epithelial origin express IFN-R1 (13). Because type III IFN cannot signal without both receptor subunits, the response to type III IFN is restricted as well. Recent work, using IFN-R1 knock-out mice, demonstrated that IFN-is effective against influenza virus, if the virus is administrated through the intranasal route, b...

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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.

Background:The class I cytokine IL-21 exerts pleiotropic effects on innate and adaptive immunity. Results: We obtained the crystal structure of the partially glycosylated IL-21 receptor (IL-21R) bound to IL-21. Conclusion: A sugar chain is an integral part of IL-21R. Significance: This structure offers an insight into the putative role of the class I cytokine receptor signature motif. IL-21 is a class I cytokine that exerts pleiotropic effects on both innate and adaptive immune responses. It signals through a heterodimeric receptor complex consisting of the IL-21 receptor (IL-21R) and the common ␥-chain. A hallmark of the class I cytokine receptors is the class I cytokine receptor signature motif (WSXWS). The exact role of this motif has not been determined yet; however, it has been implicated in diverse functions, including ligand binding, receptor internalization, proper folding, and export, as well as signal transduction. Furthermore, the WXXW motif is known to be a consensus sequence for C-mannosylation. Here, we present the crystal structure of IL-21 bound to IL-21R and reveal that the WSXWS motif of IL-21R is C-mannosylated at the first tryptophan. We furthermore demonstrate that a sugar chain bridges the two fibronectin domains that constitute the extracellular domain of IL-21R and anchors at the WSXWS motif through an extensive hydrogen bonding network, including mannosylation. The glycan thus transforms the V-shaped receptor into an A-frame. This finding offers a novel structural explanation of the role of the class I cytokine signature motif.IL-21 is a class I cytokine with a four-helix bundle structure arranged in an up-up-down-down topology typical for the class I cytokines (1). It exerts pleiotropic effects on both innate and adaptive immune responses. IL-21 is secreted by activated CD4 ϩ T cells, in particular T H 17 and T follicular helper cells, as well as natural killer cells (2). Not only do both T H 17 and T follicular helper cells produce IL-21, but this cytokine also plays an important role in promoting the development of T H 17 and T follicular helper cells by a feed-forward mechanism (3-8). Furthermore, IL-21 cooperates with other cytokines to increase the cytotoxicity of CD8 ϩ T cells and promotes proliferation of CD8 ϩ cells in the presence of antigens (9). IL-21 also influences antibody production by B cells (10). Recent studies demonstrated that IL-21 produced by CD4 ϩ cells is critical for the ability of CD8 ϩ T cells to control viral infection (11-13). The ability of IL-21 to augment immunity has spurred substantial interest in the therapeutic use of IL-21, and it is currently being evaluated in a number of clinical trials against, for example, metastatic melanoma and renal cancer (14).IL-21 signals through a heterodimeric receptor complex consisting of the private chain IL-21 receptor (IL-21R) 2 and the common ␥-chain (␥C), the latter being shared by IL-2, IL-4, . Upon binding of IL-21 to the receptor complex and subsequent receptor activation, signaling occurs through the Jak-STAT ...