Thymus lymphocytes in rats during induction of bladder tumors and effects of thymosin fraction 5 in vitro.

Bladder tumors were induced in Wistar rats by oral administration of N-butyl-N-(4-hydroxybutyl)nitrosamine [(BBN) CAS: 3817-11-6], after which changes in bladder mucous membranes and in the response of thymus lymphocytes to concanavalin A (Con A) were studied. The response of thymus lymphocytes to Con A began to decrease from the 8th week after BBN administration, with changes such as hypertrophy or vascular formation in the bladder membrane. The response decreased markedly from the 15th week, when the tumors became visible. At about the 20th week, approximately 95% of the rats had bladder tumors. When thymus lymphocytes were pretreated with thymosin fraction 5 extracted from calf thymus, the response to Con A improved between the 8th and 20th weeks. When the thymus small-lymphocyte population was separated into lighter, intermediate, and heavier subpopulations by discontinuous density gradient centrifugation and an adhesion column, the effect of thymosin fraction 5 was much greater in the lighter subpopulation.