B220⁺ NK cells exhibit close homology to CD27⁺ NK cells. (A) Gating strategy for sorting B220⁺, CD27⁺, and CD27⁻ NK-cell subsets from the spleen of B6.Rag1^−/− mice. B220⁺ NK cells are selected as CD11c^lowB220⁺CD122⁺ cells, whereas CD27⁺ and CD27⁻ NK-cell subsets are CD11c^−/lowB220⁻CD122⁺ cells and are further separated according to CD27 expression. (B) The function of B220⁺, CD27⁺, and CD27⁻ NK-cell subsets from B6.Rag1^−/− mice is depicted by their cytotoxic activity toward ⁵¹Cr-labeled YAC-1 cells. The percentage-specific lysis is shown for B220⁺ NK cells (round), CD27⁺ NK cells (square), and CD27⁻ NK cells (triangle). Results are representative of ≥ 3 experiments. (C-D) Hierarchical clustering of differentially expressed genes among B220⁺, CD27⁺, and CD27⁻ NK-cell subsets. Three hundred twenty-six genes with an adjusted P value < .05 and an absolute fold change > 1.5 in any of the 2 comparisons (CD27⁺ vs B220⁺; CD27⁻ vs B220⁺) were considered differentially expressed. (C) Gene clustering heat map is shown with the red-green scale presenting the z-transformed intensities whereby red represents a relative increase in expression and green represents a relative decrease. (D) a sample clustering dendrogram is represented from data in panel C.