Steady-state NF-κB activation in BM and splenic NK cells. (A) NF-κB activation was assessed using κB-lacZ transgenic mice having the β-galactosidase gene driven by a κB responsive promoter.^29,30  Increasing NF-κB activity is correlated with increasing fluorescence. NF-κB activity is shown on BM and splenic B (CD19⁺) and NK (CD3^-NK1.1⁺) cells of κB-lacZ mice (bold lines) and nontransgenic littermate controls (shaded histograms). (B) Steady-state NF-κB activity in NK cell subsets. Splenic NK cells (CD3^-NK1.1⁺) were electronically gated and analyzed for expression of CD43, CD45R, or CD117. NF-κB activity is shown on NK cells gated from κB-lacZ mice (bold lines) and nontransgenic littermate controls (shaded histograms) gated for -/lo versus +/hi expression of the indicated markers. Mean fluorescence intensities (MFIs) of cells are indicated (background levels in nontransgenic mice/levels in κB-lacZ mice).