DIO induces thymic involution. (A) Compared with chow-fed control male mice, the thymus appeared “fatty” in age-matched 13-month-old DIO animals along with increased body weight and reduced total thymic cell numbers (n = 12 per group). (B) The hematoxylin and eosin–stained sections of 13-month-old control and DIO mice showed increased perithymic fat and obliteration of CMJ. (C) FACS analysis of CD4-FITC– and CD8-PE–stained thymocytes. The 13-month-old DIO mice had significant reduction in SP CD4 (bottom right quadrant) and CD8 (top left quadrant) and in double-positive cells (top right quadrant). (D) The annexin-V staining on CD4 SP and CD8 SP cells showed a statistically significant (P < .05) increase in the frequency of apoptosis. Data are expressed as mean ± SEM from 8 to 12 mice per group. Images were acquired using Zeiss Axioskope microscope (10× and 20× objectives) and Axiovision Rel 4.6 software.