Working in negative space: Type I interferon mediated immuno-modulation through transcriptional suppression in disease and homeostasis.

The type I interferon family of cytokines are rapidly produced following innate pattern recognition receptor engagement and establish a critical early state of host defense. Type I interferons act in antiviral immunity as transcriptional activators and the binding of any type I interferon to the common IFNAR receptor triggers the transcription of nterferon timulated enes (ISGs). A defined set of ISGs have been described through exhaustive studies and the protein products of these ISGs function to increase cell intrinsic resistance to viral growth and to promote viral clearance. Simultaneously, interferons also drive a much less well studied program of transcriptional suppression, inhibiting the expression of an unknown number of genes, with poorly understood consequences for disease. The limited number of genes currently known to be transcriptionally suppressed by IFN are enriched for those with immune-mediating activities such as inflammatory cytokines (e.g., IL-1β), cytokine receptors (e.g., IFNγR) and chemokines. Interferon dependent transcriptional suppression of immune response genes is therefore thought to underlie the immune suppression associated with interferon production during many bacterial infections (e.g., mycobacterium tuberculosis and listeria monocytogenes) and may also explain the palliative effects of interferons in some autoimmune diseases. Despite the health relevance of IFN driven transcriptional suppression, no consensus molecular model exists to explain its selectivity or regulation. In this review we highlight the current literature detailing the known targets of IFN transcriptional suppression within the various disease models in which it has been observed. We also review the relevant molecular mechanisms which have been proposed to explain transcriptional suppression by interferons and discuss the remaining open questions in this field with an ambition to stimulate future work in this area.