Selective depletion of lymphoid tissue by cyclophosphamide.

Selective depletion of lymphocytes from the lymph follicles and cortico-medullary junction in lymph nodes and equivalent non thymus dependent areas of the spleen can be produced by cyclophosphamide (CY) (300 mg/kg) in the mouse and guinea-pig. Despite three such injections on alternate days, thymus dependent areas still contained lymphocytes. Total depletion of lymphocytes from lymph nodes and spleen was produced by combining neonatal thymectomy in the mouse or ALS treatment in the guinea-pig with CY. CY produced depletion of lymphocytes in the cortex of the thymus before the medulla. Maximal depletion occurred at 3 days and in surviving animals repopulation was evident by 7 days at the cortico-medullary junction only. Lymph follicles were found in lymph nodes of neonatally thymectomized CY treated mice following repopulation with bone marrow. These findings suggest that the lymphocytes of the lymph follicles are derived from a population of rapidly dividing cells, part of which at least can be found in the bone marrow.