The type I interferons (IFNs) are a family of cytokines discovered by their ability to protect from viral infection and realised to also modulate responses to bacteria both directly or via regulation of virtually every immune effector cell. These IFNs are encoded by a family of genes including 14 IFNa subtypes, IFNb, IFNe and IFNk, located in a locus on human chromosome 9p. It is an ongoing debate whether the type I IFNs represent functional redundancy or have specific functions. All type I IFNs act through conserved receptors IFNAR1 and IFNAR2 to activate JAK/STAT signalling pathways and similar biological responses.
IFNb appears to have functional differences because it has unique regulation of expression, by LPS, other pathogens particularly bacteria and physiological production in myeloid lineage cells. We have recently demonstrated that IFNb can also interact with a receptor component, IFNRA1, differently to other type I IFNs and transmit unique signals with important in vivo functional consequences ( de Weerd et al., Nature Immunology 2013). Another example of specific function is IFNe which we discovered to be exclusively expressed in the female reproductive tract where it regulates immune responses to bacterial and viral infections in a different manner to other type I IFNs ( Fung & Mangan et al., Science 2013). However, there is less clear evidence for different functions for the numerous IFNa subtypes which will also be discussed.