Short-term IL-7 administration results in preferential accumulation of naive T cells and TRECs in the lymph nodes of thymus-intact and thymectomized mice. Thymus-intact (A-F) and thymectomized (G-L) mice were given rmIL-7 (▪) by continuous infusion at a dose of 5 μg per day, or diluent only (▦), for 7 days or 14 days. Following the 7-day treatment course, numbers of naive (CD44lo) CD4⁺ and CD8⁺ cells (A,G), Ki67 expression (B,H), organ TREC frequency (C,I), and total organ TREC number (D,J) were determined. TREC frequency (E,K) and total organ TREC number (F,L) following 14 days of rmIL-7 treatment are also shown. Shown are combined data from 2 to 3 experiments, with mean plus or minus SD of 7 to 12 mice per group. ^*P < .05 when comparing rmIL-7 treatment to diluent by the Mann-Whitney U test. In both thymus-intact and thymectomized mice, statistically significant differences in naive cell number and total TRECs between the lymph nodes and spleen of rmIL-7-treated mice (A,D; G,J) are indicated by brackets after 7 days of rmIL-7 treatment, and after 14 days of rmIL-7 treatment in thymus intact mice (F).