Alterations in number and phenotype of NK cells in various organs of aged mice. (A) Cells from the indicated organs from young and aged naive mice were stained for surface CD3, NK1.1, CD27, CD11b, and CD62L and analyzed by flow cytometry. For blood, mononuclear cells were isolated by ficoll-hypaque centrifugation. For the liver, mononuclear cells were isolated by centrifugation in a Percoll gradient. Data are representative of two to four similar experiments. P-values are for two-tailed Student’s t tests. (B) As in A, but displaying the proportion of R3 cells. (C) As in A, but displaying the proportion of R1 cells in the total NK cell population. (D) As in A, but displaying the proportion of the indicated NK population in the blood that was CD62L⁺. (E) As in A, but displaying the proportion of R3 NK cells in the indicated organs that was CD62L⁺. P-values are for two-tailed Student’s t tests. For all panels, the horizontal bars indicate the mean and the vertical bars the SEM.