The effect of neonatal thymectomy on the ontogeny of mitogen responses in the quokka ( Setonix brachyurus)

Abstract

The lymphocyte responses to phytohaemagglutinin (PHA), Concanavalin A (Con A), and Pokeweed mitogen (PWM) were determined at various intervals throughout pouch life in the quokka ( Setonix brachyurus). The responses to both PHA and Con A of lymphocytes from the blood and mesenteric lymph node of thymectomised pouch young were significantly depressed, indicating that these mitogens stimulate thymus-dependent lymphocytes. In contrast to most other vertebrates, splenic leucocytes from intact pouch young responded poorly to stimulation with these mitogens: after neonatal thymectomy the responses were slightly, but not significantly, depressed. Peripheral blood lymphocytes from thymectomised quokkas showed a significantly decreased responsiveness to PWM at 100 and 140 days of age, but the response of lymphocytes from other sources was not significantly different from that of intact animals at comparable ages. There were no significant trends with age in the mitogen responses of lymphocytes from thymectomised pouch young. These data are discussed in relation to the spontaneous restoration of immune responsiveness which occurs after the end of reserves of immunocompetent lymphocytes which had been built up.