| Description |
Stain: Immunoperoxidase staining with diaminobenzidin (DAB) and hematoxylin counterstained on frozen section. A single injection with cyclophosphamide (CP, 70 mg/ml) induces a transient cortical involution after 4 days, i.e. the darkly stained cortex and the lightly stained medulla in normal thymus (A1, A2) turn to darkly stained medulla and a lightly stained cortex (B1, B2) four days after a single injection with CP. The thymus recovers to normal about 10 days later. (C) shows a negative immunoperoxidase control of a normal thymus. The anti-CD8 monoclonal antibody in normal thymus tissue (A1, A2) shows an intense cortical staining, while in the medulla (A2-1) the positively stained cells are much less, since the medulla contains single-positive CD8 cells, while the cortex contains both double-positive (CD4+CD8+) and single positive lymphocytes (CDE8+). The large CD4+ CD8+ population harbours the majority of dividing thymocytes. Due to the CP-induced inhibition of cell proliferation in the cortex (B1, 2) the remaining cortical thymoblasts hardly express CD8, while the medullar thymocytes are strongly positive, confirming the so-called transient thymic inversion. (A1, A2): Normal thymus. (B1, B2): CP-treated thymus. (C): A negative immunoperoxidase control. (1) medulla; (2) cortex; (3) septa or trabeculae. |
