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.