Interferons are a diverse family of cytokines with critical roles in immunity. In the Journal of Experimental Medicine, Quintana-Murci and colleagues use population genetics to delineate the relative importance of members of the interferon family in human immunity. Interferons are categorized into three families according to the receptors they bind and their functional and signaling properties: type I (INF-α1–INF-α13, INF-β, INF-ε, INF-κ and INF-ω), type II (INF-γ) and type III (INF-λ1–INF-λ3). By looking at the mutation frequency of genes encoding the various interferons and how this relates to different geographical distributions (Africa, Europe and Asia), they are able to gauge the contribution to host survival. Notably, IFN-γ and, to a lesser extent, IFN-α6, IFN-α8, IFN-α13 and IFN-α14 show strong purifying positive selection in all populations, which suggests critical nonredundant functions in immunity to infection. Furthermore, strong positive selection is also seen for type III interferons, but only in Eurasian populations, probably as an adaptive response to specific pathogen exposure in this geographical locale.

J. Exp. Med. (12 January 2012) doi:10.1084/jem.20111680