The effect of cyclophosphamide on CD3-thymocytes in thymus (rat)

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 dark-blue 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-CD3 monoclonal antibody shows low staining in the normal cortex (A1-2), but medullar thymocytes are CD3+ (A1-1 and A2-1). CD3 expression increases on all T cells upon maturation of the cells as they migrate towards the medulla. Figure B1 and B2 show that, after CP treatment the strong CD3+ expression in the medulla (B1-1, B2-1) remains unaltered since these non-mitotic cells are not affected by CP. CD3 remains low in the cortex (B2-2). After ten days (C) the cortex and medulla pattern are repopulated to normal levels as shown in A.