Non-conventional interferons : characterization of interferon epsilon (IFN-ε) and specificities of the interferon lambda (IFN-λ) response in the liver
(2014)
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- Authors
- Supervisors
- Michiels, Thomas
- Abstract
- Interferons (IFNs) are a family of class II cytokines playing a role of mediators against pathogens in vertebrates. They have antiviral activity, as well as antiproliferative and immunomodulatory activities. IFNs are grouped into three classes and called type I, II and III IFNs, according to their functions, amino acid sequences, and receptor usage. There is a great multiplicity among IFN genes, and the objective of this thesis was to better understand why such a multiplicity exists. Among type I IFNs, IFN-α and IFN-β are the most well-known and act both locally and systemically to control viral infection. However, other type I IFNs are less characterized and appear to be devoted to the protection of specific tissues or cells. This is the case for IFN-ε. The first part of this work was based on an observation made by Caroline Sommereyns in our laboratory who noticed that supernatants from cells transfected with a pcDNA3-IFN-ε plasmid had no antiviral activity. We analyzed IFN-ε expression in vivo and noticed its constitutive expression in mouse reproductive organs. Surprisingly, IFN-ε expression was not induced upon viral infection. Using plasmid constructs expressing FLAG-tagged IFN-ε and chimeric constructs produced between IFN-ε and limitin (IFN-ζ), a mouse type I IFN, we also noticed that the cleavage of the IFN-ε signal peptide was inefficient in various cell lines, and that both the signal peptide and the mature moiety of IFN-ε contributed to this poor processing. Immunofluorescent detection of FLAG-tagged IFN-ε in transfected cell lines and fibroblasts allowed us to highlight a probable defect in the progression of the cytokine through the secretory pathway. These observations led us to the hypothesis that IFN-ε secretion is tightly regulated and that its secretion may require a co-factor specifically expressed in cells of the reproductive organs, securing the system against secretion of this IFN from other cells. The second part of this work focuses on type III IFNs, which were discovered only 10 years ago. This group of cytokines comprises four subtypes: IFN-λ1 to -λ4. Type III IFNs signal through a heterodimeric receptor composed of two chains: IFNλR1, which is specific to IFN-λ, and IL-10R2, which is shared by other IL-10 related cytokines. Unlike the type I IFN receptor, which is expressed ubiquitously, IFNλR1 is preferentially expressed by epithelial cells. Recently, IFN-λ1 entered phase 3 clinical trials as a candidate drug against hepatitis C virus (HCV) infection. Because of its epithelial specificity, IFN-λ is expected to be a good alternative to type I IFNs for the treatment of some viral diseases, as less side effects are expected due to the more restricted range of IFN-λ target cells. Surprisingly, the mouse liver responds poorly to IFN-λ, in spite of the epithelial nature of hepatocytes. Here, we found that, although mouse hepatocytes can respond to IFN-α, they do not respond to IFN-λ. Instead, the response to IFN-λ in mouse liver was restricted to choliangocytes, the epithelial cells forming the bile ducts. Next, we used a model of chimeric mice that were transplanted with human hepatocytes to show that human but not mouse hepatocytes are responsive to IFN-λ under identical experimental conditions in vivo. Finally, we have investigated the polarization of the IFN-λ response in epithelial cells. We found that both the apical and the basolateral poles of epithelial cells were responsive to IFN-λ in vitro, suggesting that the IFN-λ receptor is equally distributed between the apical and basolateral sides of these cells. On the contrary, IFN-α mainly acts on the basolateral side of epithelia. Our observations suggest that IFN-λ may allow a more localized response if secreted in the lumen of some organs.
- Affiliations
Citations
Hermant, P. (2014). Non-conventional interferons : characterization of interferon epsilon (IFN-ε) and specificities of the interferon lambda (IFN-λ) response in the liver. https://hdl.handle.net/2078.5/202940