In vitro lymphopoiesis in foetal thymic organ cultures: effect of various agents

In this study 14-day-old foetal BALB/c mouse thymic lobes were removed and grown as organ culture in vitro for up to 6 days. The cultures were treated with agents which are known to alter the intracellular levels of cyclic nucleotides. The proliferative response of the lobes was judged by histological examination, 125I-UdR uptake and cell yields, of the lobes at various time intervals. The results indicate that agents which raise cyclic GMP levels stimulate the proliferative response of the lobes as judged by the various parameters used and that the response was largely restricted to the lymphoid cells. It has been suggested that most probably cyclic GMP is the positive signal for thymic lymphopoiesis perhaps not only in vitro but also in vivo.