B220⁺ NK cells are actively cycling. (A) Heat map of the mRNA expression of the genes from clusters VI and VII on DAVID Functional Enrichment analysis, wherein higher mRNA expression was observed in B220⁺ NK cells relative to both CD27⁺ and CD27⁻ NK cells. Z-transformed intensities are visualized by a red-green color scale whereby red represents a relative increase in expression and green a relative decrease. (B) Cell cycle analysis was performed on B220⁺, CD27⁺ and CD27⁻ NK cells, as well as total CD49b⁺ NK cells sorted from the spleen of C57BL/6 mice. The percentage of cells in each phase on the cell cycle is represented. Mann-Whitney U test was applied to obtain P values that compared B220⁺ NK cells with other cell types (n = 5).