Cellular changes in the bursa of Fabricius and thymus of cyclophosphamide-treated pigeons

The histological changes occurring in the bursa of Fabricius and in the thymus of 4-week-old pigeons after cyclophosphamide (Cy)-treatment are described. The bursa underwent atrophy and lymphoid cells virtually disappeared from the follicles in which only the reticulo-epithelial cells persisted. The thymus also showed marked degeneration accompanied by lymphocyte depletion. The development of lesions ceased 4 days after the beginning of treatment in the thymus and 6 days later than this in the bursa. After 2 weeks, the two organs showed regeneration. The histological appearance of the thymus returned to normal after 3 weeks and that of the bursa after 7 weeks. Cy-treatment of pigeons produced a profound B and T-cell deficiency which is more transient for T-cells.