Although murine NK cells are known to respond to IL‐2 by proliferation and enhanced cytotoxic function 36, it has long been assumed that this response is mediated by the low‐affinity IL‐2R as studies in the early 1990s failed to detect expression of IL‐2Rα (CD25) in murine NK cells after in vivo administration of IL‐2 or IFN‐β or after infection with lymphocytic choriomeningitis virus 36. This evidence concerns the gene IFNB1 and infection.