Natural killer (NK) cells are important innate effectors that play a pivotal role in the defense against tumors and infections and participate in regulating adaptive immunity.Recent studies have revealed phenotypic and functional heterogeneity of NK cells.Here,using murine models of acute and chronic lymphocytic choriomeningitis virus infection,we observed that a CD49a+ CD49b+ NK cell subset emerged in the liver and other tissues,and underwent vigorous expansion following viral infection,before progressively decreasing in cell number.These viral infection-induced CD49a+CD49b+ NK cells displayed an activated and mature phenotype.Moreover,compared with liver-resident NK cells and conventional NK (cNK) cells,CD49a+CD49b+ NK cells showed increased functional competence,as evidenced by higher amounts of IFN-γ,production and stronger cytotoxic capabilities during viral infection.Generation of these CD49a+CD49b+ NK cells was shown to be independent of the T-bet transcription factor.Adoptive transfer experiments revealed that cNK cells could convert into CD49a+CD49b+ NK cells following viral infection.Collectively,these results suggest that viral infection-induced CD49a+CD49b+ NK cells represent a transiently activated state of eNK cells.