Thymus after cyclophosphamide treatment (rat)

Stain: Hematoxylin & eosin. A single injection with cyclophosphamide (CP, 4 70 mg/ml) induces a transient cortical involution, i.e. inhibition of the cell proliferation and maturation. A: Normal thymus with medulla (1) and cortex (2). B1: Inversion of thymic cortex and medulla 4 to 8 days after CP treatment, i.e. the cortex is lightly stained due to exit of T cells into the medulla without a concomitant supply of new T cells in the cortex. The medulla is stained darkly. B2: Detail of B1 showing a majority of blast-like cells in the cortex and nearly no small T cells, while the medulla (1) contains predominantly small, darkly stained lymphocytes. C: Recovery of the normal situation two weeks later. The CP treatment causes transiently an immunosupression of the antibody response.