During the preparation of our manuscript Sun et al. published that an infection with mouse CMV (MCMV) elicits a massive expansion of NK cells (72-fold within 7 days) in IL-15Rα-deficient mice and that these NK cells can be activated in vitro for the expression of IFN-γ and target cell cytotoxicity 42. The gene discussed is IL15RA; the disease is infection.