Changes in gross thymic morphology and histology of old WT and Foxn1 Tg mice (line 60). (A) Gross thymic morphology of a 26-month-old WT mouse with adipose tissue present (arrows). (B) H&E staining of the same thymus shows the loss of cortical-medulla demarcation and the abundance of adipose tissue (*). (C) Gross thymic morphology of a 31-month-old Foxn1Tg mouse with intact parenchymal tissue with little adipose tissue deposition. (D-F) H&E staining of the same thymus shows a clear cortical-medulla demarcation and little adipose tissue deposition. Images were acquired with a Leitz Diaplan microscope with a 25×/0.6 W (B-D) and 50×/1.0 W equipped with Religa 2000R camera and QImaging Pro software (Version 6.0). Scale bars represent 50 μm.