Exogenous IGF-1 symmetrically expands TEC populations and increases their turnover. (A) Thymic weights of diluent-treated control mice and mice treated for 14 days with IGF-1. Shown are combined data of 4 experiments with 11 mice per group. Error bars represent SEM. *P < .05 between IGF-1– and diluent-treated mice. (B) Light microscopy image of thymus sections of diluent-treated and IGF-1–treated mice. Images (100× magnification) are representative of 3 mice per group. (C) Representative confocal images (200× magnification) of thymi from diluent-treated and IGF-1–treated mice identifying major cortical (red; K5⁻ K8⁺), minor cortical (yellow; K5⁺ K8⁺), and major medullary (green; K5⁺ K8⁻) TEC subsets. (D) Representative confocal images (100× magnification) of thymi identifying minor cortical (red; K5⁺ K14⁻ UEA-1⁻), major medullary (pink; K5⁻ K14⁻ UEA-1⁺), and minor medullary (green; K5⁻ K14⁺ UEA-1⁻) TEC subsets. Images are representative of 4 to 6 sections per animal, 3 animals per experimental group. (E) TECs were isolated from thymi of IGF-1–treated and diluent-treated control mice by enzymatic digestion. By flow cytometry, cortical TECs (cTECs) were identified phenotypically as CD45⁻ Ly51⁺ UEA-1⁻, and major medullary TECs (mTECs) were identified phenotypically as CD45⁻ Ly51⁻ UEA-1⁺. For each TEC population, the total number of TECs and their relative proportion to the entire nonhematopoietic CD45⁻ population was calculated. These values were then compared with the total number of thymocytes to compare their relative changes with IGF-1 treatment. Graphs represent the relative fold changes between IGF-1–treated and diluent-treated control mice on day 4 and day 14 of IGF-1 administration in the following parameters: relative percentage of cortical and medullary TECs (), total cortical and medullary TECs (), and total thymocyte numbers (). Shown are combined data from 3 independent experiments with TECs isolated from 3 thymi per group per experiment. (F) For measurements of TEC turnover, continuous BrdU was administered into mice for 5 days, from day 2 to day 7 and from day 9 to day 14, after which BrdU incorporation in sorted cortical and medullary TECs was measured. Shown are representative results from 2 independent experiments, with 3 thymi per group per experiment. Error bars represent SEM. *P < .05 between IGF-1– and diluent-treated mice.