Interferons (IFN) exert antiviral, immunomodulatory and cytostatic activities. IFN-α/β (type I IFN) and IFN-λ (type III IFN) bind distinct receptors, but regulate similar sets of genes and exhibit strikingly similar biological activities. We analyzed to what extent the IFN-α/β and IFN-λ systems overlap in vivo in terms of expression and response. We observed a certain degree of tissue specificity in the production of IFN-λ. In the brain, IFN-α/β was readily produced after infection with various RNA viruses, whereas expression of IFN-λ was low in this organ. In the liver, virus infection induced the expression of both IFN-α/β and IFN-λ genes. Plasmid electrotransfer-mediated in vivo expression of individual IFN genes allowed the tissue and cell specificities of the responses to systemic IFN-α/β and IFN-λ to be compared. The response to IFN-λ correlated with expression of the α subunit of the IFN-λ receptor (IL-28Rα). The IFN-λ response was prominent in the stomach, intestine and lungs, but very low in the central nervous system and spleen. At the cellular level, the response to IFN-λ in kidney and brain was restricted to epithelial cells. In contrast, the response to IFN-α/β was observed in various cell types in these organs, and was most prominent in endothelial cells. Thus, the IFN-λ system probably evolved to specifically protect epithelia. IFN-λ might contribute to the prevention of viral invasion through skin and mucosal surfaces. Virus-infected cells can secrete interferons (IFNs), cytokines that induce an infection-resistant state in neighboring cells. IFNs are critical to slow down early multiplication of pathogens in the body. Two IFN families exhibiting strikingly similar properties were described: type I IFNs (or IFN-α/β) and type III IFNs (or IFN-λ). Our work addressed the question of the redundancy of these two IFN systems in vivo. First, we found that the relative expression of IFN-λ over that of IFN-α/β exhibited some extent of tissue specificity and was low in the brain. Next, we used a strategy based on in vivo expression of cloned IFN genes to compare the responses of different tissues to IFN-α and IFN-λ. As was suggested by previous in vitro work, response to IFN-λ appeared to be restricted to epithelial cells, unlike response to IFN-α which occurred in most cell types. Tissues with a high epithelial content such as intestine, skin or lungs were the most responsive to IFN-λ and expressed the higher amounts of IFN-λ receptor. Our data suggest that the IFN-λ system evolved as a specific protection of epithelia and that it might contribute to prevent viral invasion through skin and mucosal surfaces.

Virus-infected cells secrete a broad range of interferons (IFN) which confer resistance to yet uninfected cells by triggering the synthesis of antiviral factors. The relative contributions of the various IFN subtypes to innate immunity against virus infections remain elusive. IFN-α, IFN-β, and other type I IFN molecules signal through a common, universally expressed cell surface receptor, whereas type III IFN (IFN-λ) uses a distinct cell-type-specific receptor complex for signaling. Using mice lacking functional receptors for type I IFN, type III IFN, or both, we found that IFN-λ plays an important role in the defense against several human pathogens that infect the respiratory tract, such as influenza A virus, influenza B virus, respiratory syncytial virus, human metapneumovirus, and severe acute respiratory syndrome (SARS) coronavirus. These viruses were more pathogenic and replicated to higher titers in the lungs of mice lacking both IFN receptors than in mice with single IFN receptor defects. In contrast, Lassa fever virus, which infects via the respiratory tract but primarily replicates in the liver, was not influenced by the IFN-λ receptor defect. Careful analysis revealed that expression of functional IFN-λ receptor complexes in the lung and intestinal tract is restricted to epithelial cells and a few other, undefined cell types. Interestingly, we found that SARS coronavirus was present in feces from infected mice lacking receptors for both type I and type III IFN but not in those from mice lacking single receptors, supporting the view that IFN-λ contributes to the control of viral infections in epithelial cells of both respiratory and gastrointestinal tracts.

Type I and type III IFNs bind to different cell-surface receptors but induce identical signal transduction pathways, leading to the expression of antiviral host effector molecules. Despite the fact that type III IFN (IFN-λ) has been shown to predominantly act on mucosal organs, in vivo infection studies have failed to attribute a specific, nonredundant function. Instead, a predominant role of type I IFN was observed, which was explained by the ubiquitous expression of the type I IFN receptor. Here we comparatively analyzed the role of functional IFN-λ and type I IFN receptor signaling in the innate immune response to intestinal rotavirus infection in vivo, and determined viral replication and antiviral gene expression on the cellular level. We observed that both suckling and adult mice lacking functional receptors for IFN-λ were impaired in the control of oral rotavirus infection, whereas animals lacking functional receptors for type I IFN were similar to wild-type mice. Using Mx1 protein accumulation as marker for IFN responsiveness of individual cells, we demonstrate that intestinal epithelial cells, which are the prime target cells of rotavirus, strongly responded to IFN-λ but only marginally to type I IFN in vivo. Systemic treatment of suckling mice with IFN-λ repressed rotavirus replication in the gut, whereas treatment with type I IFN was not effective. These results are unique in identifying a critical role of IFN-λ in the epithelial antiviral host defense.

A dynamic mathematical model was developed to describe the uptake of various carbohydrates (glucose, lactose, glycerol, sucrose, and galactose) in Escherichia coli. For validation a number of isogenic strains with defined mutations were used. By considering metabolic reactions as well as signal transduction processes influencing the relevant pathways, we were able to describe quantitatively the phenomenon of catabolite repression in E. coli. We verified model predictions by measuring time courses of several extra- and intracellular components such as glycolytic intermediates, EII-A^Crr phosphorylation level, both LacZ and PtsG concentrations, and total cAMP concentrations under various growth conditions. The entire data base consists of 18 experiments performed with nine different strains. The model describes the expression of 17 key enzymes, 38 enzymatic reactions, and the dynamic behavior of more than 50 metabolites. The different phenomena affecting the phosphorylation level of EIIA^Crr, the key regulation molecule for inducer exclusion and catabolite repression in enteric bacteria, can now be explained quantitatively.

Upon incubation at 37 degrees C in the absence of Ca2+ ions, pathogenic yersiniae release large amounts of pYV plasmid-encoded proteins called Yops that are involved in pathogenesis. Yersinia enterocolitica also expresses an outer membrane protein that is considered an adhesin and called YadA (previously called P1 or YopA). The production of Yops is coordinately regulated by a 20-kb region of the plasmid referred to as the Ca2+ dependence region and containing at least four loci called virA, virB, virC, and virF. The virF gene encodes a key transcriptional activator of yop genes. We have shown here that virF is also required for transcription of yadA and that virB is necessary for full transcription of the yop and yadA genes. In contrast, mutations in genes virA and virC had only a weak influence on the transcription of yop and yadA genes. These mutations did not affect the production of YadA but they completely inhibited the translocation of Yops from the intracellular compartment to the extracellular milieu. We inferred from these data that virA and virC are involved in the specific transport of Yops. We analyzed the 8.5-kb virC region and showed that it is most probably a single operon containing 13 open reading frames called yscA to yscM (for Yop secretion). Protein YscC has a putative signal sequence and shares significant homology with outer membrane proteins involved in the secretion of pullulanase by Klebsiella pneumoniae (PulD) or in the assembly of filamentous bacteriophages (gene IV product). At least the putative products of yscD, yscJ, and yscL were shown to be required for the export of Yops. YscJ turned out to be YlpB, a lipoprotein that we had detected previously. The yscM gene shares homology with yopH, the adjacent gene on the pYV plasmid. Its product does not appear to be necessary for the production of Yops. Transcription of the virC operon was subjected to the same regulation as the yop genes.

Type I interferons, also referred to as IFN-α/β, form the first line of defense against viral infections. Major IFN-α/β producers in the periphery are the plasmacytoid dendritic cells (pDCs). Constitutive expression of the IFN regulatory factor (IRF)-7 enables pDCs to rapidly synthesize large amounts of IFN-α/β after viral infection. In the central nervous system (CNS), pDCs are considered to be absent from the parenchyma, and little is known about the cells producing IFN-α/β. The study presented here aimed to identify the cells producing IFN-α/β in the CNS in vivo after infection by neurotropic viruses such as Theiler's virus and La Crosse virus. No cells with high constitutive expression of IRF-7 were detected in the CNS of uninfected mice, suggesting the absence of cells equivalent to pDCs. Upon viral infection, IFN-β and some subtypes of IFN-α, but not IFN-ε or IFN-κ, were transcriptionally up-regulated. IFN-α/β was predominantly produced by scattered parenchymal cells and much less by cells of inflammatory foci. Interestingly, in addition to some macrophages and ependymal cells, neurons turned out to be important producers of both IFN-α and IFN-β. However, only 3% of the infected neurons produced IFN-α/β, suggesting that some restriction to IFN-α/β production existed in these cells. All CNS cell types analyzed, including neurons, were able to respond to type I IFN by producing Mx or IRF-7. Our data show that, in vivo , neurons take an active part to the antiviral defense by being both IFN-α/β producers and responders.