Construction of the lck–IL-7 transgene and IL-7 expression in Tg⁺ and B6 mice. (A) The construct included 3 kb of the lck proximal promoter, 533 bp of IL-7 murine cDNA containing the whole coding murine sequence, and 2 kb of the intron post stop codon of the 3′ human growth hormone (hGH).26 (B-C) Comparison of thymic IL-7 expression among the 3 founder lines of IL-7 Tg and negative controls in newborn and 6- to 8-week-old mice, respectively. Real-time PCR was performed for IL-7 expression and normalized to HPRT expression. Results were presented as the ratio of IL-7 (fg)/HPRT (fg) expression. (B) Total thymocyte tissue was used to determine IL-7 expression in day-1 newborn mice. The numbers of mice were as follow: TgA = 5, TgH = 3, TgB = 4, and negative littermates n = 8. (C) DP, CD4SP, and CD8SP cells from adult thymi were positively selected as described in “Materials and methods” and compared with thymic tissue from normal B6 mice. Error bars indicate SEM. (D) In situ hybridization with IL-7 RNA probe. Representative sections from the thymus of TgA, TgH, TgB, and normal B6 mice showing the localization of IL-7 expression to the cortex “C” and the medulla “M.”