Adult mice double deficient in Fl and Il7r expression have severely reduced numbers of naive T cells: evidence for clonal expansion of peripheral T cells. PB (A) and spleen (B-D) cells from 8- to 10-week-old WT, Fl^−/−, Il7r^−/−, and Fl^−/−Il7r^−/− mice were enumerated and stained with antibodies against CD4, CD8, CD44, and CD62L to establish the relative distribution between naive (CD44^low) and activated/memory (CD44^high) T cells.³⁵  (A) Total number of CD4⁺ and CD8⁺ T cells in PB. (B) Representative FACS profiles of CD44^low and CD44^high cells within CD4⁺ gate. Numbers in quadrants show mean values of 6 to 10 mice. (C,D) Total number of naive and activated/memory CD4⁺ (C) and CD8⁺ (D) T-cell subsets, respectively. (E-G) Sequences of TCR Vβ8, Vβ 5.2 D-J6 recombinations in splenocytes from one representative 8- to 10-week-old WT (E) and 2 age-matched Fl^−/−Il7r^−/− (F,G) mice. Letters indicate germ-line sequences and bold underlined text indicates insertions (N and P nucleotides). D region is indicated in italics. *P < .01, comparing Il7r^−/− and Fl^−/−Il7r^−/− mice.