Peripheral homeostasis of mature NK cells is conditioned by cytokines and the presence of endogenous NK cells. (A) CFSE dilution profiles of splenic NK cells 5 days after adoptive transfer into the indicated hosts. An electronic gate was set on CD122⁺ (IL-2Rβ⁺) cells. Boxes indicate percentages of CFSE⁺ NK cells that have not divided. ND represents not detected. (B) CD127 versus CD11b expression on electronically gated NK1.1⁺ splenocytes from Rag° mice. Isotype control staining is shown for comparison. (C) Absolute numbers of recovered splenic CD122⁺NK1.1⁺ NK cells at 5 days after transfer. Black bars (▪) indicate nondivided donor NK cells and open bars (□) indicate NK cells with more than one division. Error bars denote standard deviations.