Fig. 2

Effects of systemic sirolimus treatment on thymus histology and immunoperoxidase staining with cytochrome c and caspase 3. Mice received intraperitoneal DMSO or sirolimus on Days 0–3. Thymus fragments were then stained with H&E and immunoperoxidase with anti-cytochrome c and caspase 3 on Day 4 (Panel a) or Day 14 (Panel b). Panel a (Day 4): DMSO (control): Normal thymus histology demonstrating darkly staining lymphocyte rich cortex and pale staining medulla; few (<2 %) cortical lymphocytes with positive staining for cytochrome c and caspase 3 are present (arrow). Sirolimus: Thymic cortical involution with thinning of cortex and loss of the demarcation between the cortex and medulla; increased staining by cytochrome c and caspase 3 (about 20 % of the cells are positive). Panel b (Day 14): Normal thymus histology with a cortex rich in lymphocytes and a lymphocyte scant medulla; rare (<2 %) cortical lymphocytes with positive staining for cytochrome c are present (arrow)