A maturational defect causes reduced NK cell numbers in ItpkB^−/− mice. Splenocytes (A) and BM cells (C) from WT and ItpkB^−/− mice were stained for CD3 and NK1.1 or the indicated lineage markers, CD122, CD27, and CD11b to distinguish terminal maturational stages¹⁷  and analyzed by flow cytometry. WT level CD3⁻NK1.1⁺ NK cell (spleen; A) and CD3⁻CD122⁺ NK cell precursor (BM; C) percentages reflect the profound CD3⁺NK1.1⁻ T-cell deficiency in ItpkB^−/− mice.^26,31,32  However, CD11b⁺CD27⁻ mature NK cells were considerably reduced in ItpkB^−/− spleens and BM. (B) Paired Student t test analysis (n = 12) revealed a significant reduction (P < .0001) of total splenic NK cell numbers in ItpkB^−/− mice.