What Have We Learned from the IL28 Receptor Knockout Mouse?

The recently discovered type III interferons (IFNs), also known as IFN-lambda, are part of the early innate immune response against viral infections. The IFN-lambda system closely resembles the type I IFN (IFN-alpha/beta) system in terms of expression after virus infection as well as intracellular signaling and activation of antiviral host factors in susceptible cells. However, in contrast to type I IFN, which signals through a universally expressed cell surface receptor, IFN-lambda uses a distinct receptor complex (IL28R) for signaling, which is expressed on a limited range of cell types. Until recently both the contribution of type III IFN to antiviral resistance as well as the exact nature of IL28R-expressing cells in vivo remained elusive. In this review we discuss data obtained from the experiments with IL28R alpha(0/0) mice that demonstrated the role of IFN-lambda in viral defense in vivo. We further discuss the experiments that identified the cell types in various organs that express functional IFN-lambda receptors

Combined action of type I and type III interferon restricts initial replication of severe acute respiratory syndrome coronavirus in the lung but fails to inhibit systemic virus spread

STAT1-deficient mice are more susceptible to infection with severe acute respiratory syndrome coronavirus (SARS-CoV) than type I interferon (IFN) receptor-deficient mice. We used mice lacking functional receptors for both type I and type III IFN (double knockout, dKO) to evaluate the possibility that type III IFN plays a decisive role in SARS-CoV protection.Wefound that viral peak titres in lungs of dKO and STAT1-deficient mice were similar, but significantly higher than in wild-type mice. The kinetics of viral clearance from the lung were also comparable in dKO and STAT1-deficient mice. Surprisingly, however, infected dKO mice remained healthy, whereas infected STAT1-deficient mice developed liver pathology and eventually succumbed to neurological disease. Our data suggest that the failure of STAT1-deficient mice to control initial SARS-CoV replication efficiently in the lung is due to impaired type I and type III IFN signalling, whereas the failure to control subsequent systemic viral spread is due to unrelated defects in STAT1-deficient mice.C. D. was supported by the German Ministry of Education (project code SARS II 01KI1005A) and grants from the European Commission (FP7-ANTIGONE number 278976 and FP7-EMPERIE number 223498). L. E. was supported by a grant from the Ministry of Science and Innovation of Spain (BIO-2010-60978). P. S. was supported by a grant from the German Science Foundation (SFB620)

IFN-λ activates <i>Mx1</i> gene expression in lung but not liver of IFNAR1^0/0 mice.

<p>(A) Western blot analysis of Mx1 protein levels in lungs of mice at 20 hours post intranasal application of 3,500 units of IFN-λ3. Animals treated with a mock preparation served as control. Two animals of each group are shown. (B) Mx1 protein levels in the liver of <i>IFNAR1^0/0</i> mice at 20 hours post intraperitoneal application of 15,000 units of IFN-λ3 or terminally ill at 72 hours post infection with hepatotropic THOV-ΔML or RVFV clone 13. Two animals for each group are shown. Liver extract from a wild-type mouse killed at 20 hours post intraperitoneal treatment with 100,000 units of human IFN-αB/D served as positive control.</p

Induction of IFN-λ2 genes in virus-infected lung and liver of <i>IFNAR1^0/0</i> mice.

<p>Animals were either infected by the intranasal route with 10⁶ pfu of influenza A virus strain SC35M-ΔNS1 or PR8-ΔNS1, or else by the intraperitoneal route with 10 pfu of hepatotropic THOV-ΔML. Animals treated with plain buffer served as negative controls. At 17 hours post infection, the influenza virus-infected mice were killed and the lungs were removed for analysis. The liver of the THOV-infected mouse was harvested when the animal was severely diseased at 72 hours post infection. RNA samples from the organs were reverse transcribed and analyzed by PCR for transcripts of the indicated genes.</p

Exogenous IFN-λ protects <i>IFNAR1^0/0</i> mice against intranasal challenge with influenza A virus but not against intraperitoneal challenge with THOV.

<p>(A) Survival of mice intranasally treated for 10 hours with a mock preparation or 7,500 units of either IFN-λ2 or IFN-λ3 before challenge with 100 pfu (∼20 LD₅₀) of influenza A virus strain SC35M. (B) Survival of mice intraperitoneally treated for 10 hours with a mock preparation or 15,000 units of IFN-λ3 before infection with 100 pfu (∼20 LD₅₀) of THOV.</p

Inverse correlation of Mx1 protein levels and viral load in lungs of mice lacking functional receptors for IFN-α/β, IFN-λ or both.

<p>Groups of mice were infected with 10⁵ pfu of SC35M-ΔNS1 and either killed at (A) 48 hours post infection to determine viral titers in the lung or at (B) 20 hours post infection to determine Mx1 protein levels by western blotting. Two animals of each group are shown. Actin-normalized Mx1 signal intensities are indicated. The calculated value of the wild-type mice was set to 100%. (*: p<0.05), ***: p<0.001).</p

Mice lacking functional receptors for both IFN-α/β and IFN-λ exhibit enhanced susceptibility toward highly attenuated influenza A viruses but not toward two different attenuated hepatotropic viruses.

<p>Survival of <i>IFNAR1^0/0</i> (diamonds) and <i>IFNAR1^0/0IL28Rα^0/0</i> double knockout mice (circles) after (A) intranasal infection with the indicated doses of SC35M-ΔNS1, (B) intranasal infection with 10⁶ pfu of PR8-ΔNS1, (C) intraperitoneal infection with the indicated doses of THOV-ΔML, and (D) intraperitoneal infection with the indicated doses of RVFV clone 13. Groups consisted of four to nine animals.</p

Mice lacking functional receptors for IFN-λ show slightly reduced resistance to influenza A virus.

<p>Wild-type and <i>IL28Rα^0/0</i> mice were infected by the intranasal route with 5×10⁴ pfu of SC35M. (A) Survival and (B) virus titers in lungs at 72 hours post infection were recorded. Combined data of several independent experiments are shown. (**: p<0.01).</p

Interferon-{lambda} renders epithelial cells of respiratory and gastrointestinal tract resistant to viral infections.

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 contribution of the various IFN subtypes to innate immunity against virus infections remains elusive. IFN-alpha, IFN-beta and other type I IFN molecules signal through a common universally expressed cell surface receptor, whereas type III IFN (IFN-lambda) 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-lambda 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 SARS coronavirus. These viruses were more pathogenic and replicated to higher titers in the lung of mice lacking both IFN receptors than in mice with single IFN receptor defects. By contrast, Lassa fever virus, which infects via the respiratory tract but primarily replicates in the liver, was not influenced by the IFN-lambda receptor defect. Careful analysis revealed that expression of functional IFN-lambda receptor complexes in lung and intestinal tract is restricted to epithelial cells and 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 from mice lacking single receptors, supporting the view that IFN-lambda contributes to the control of viral infections in epithelial cells of both respiratory and gastrointestinal tract