MHC and B7-1 promote incorporation of BrdU into NK cells. RAG-1(-/-)C57BL6/j mice were injected with 10⁶/mouse of tumor cells intravenously and with 2 daily doses of BrdU intraperitoneally. Mice were killed at 48 hours after tumor cell challenge for analysis. Mononuclear leukocytes from liver (A) or spleen (B) were stained with NK1.1 mAb, and after permeabilization, incubated with anti-BrdU mAb. Data shown are profiles of gated NK1.1⁺ cells from one representative mouse in each group. The gates for BrdU⁺ cells were set based on isotype control, which gave less than 0.5% positive cells. The percentages of BrdU⁺ cells are shown in the panels. Data shown are representative of 2 independent experiments. (C) Composite data on percentages of BrdU⁺ cells of NK1.1⁺ cells from liver and spleen. Means, standard error, and statistical significance were described in the text.