Thymic lymphopoiesis and cholinergic innervation.

This study was carried out to determine whether the thymic rudiments implanted into the anterior eye chambers of syngenic hosts receive cholinergic neuronal input from the host, similar to the adrenergic neuronal input into the implants, observed in previous studies. In addition, the study was also aimed at examining the effect of this (cholinergic) neuronal input on thymic lymphopoiesis. 13/14-day-old fetal thymic rudiments were implanted into the anterior eye chambers of syngenic (BALB/c) mice. They were removed at weekly intervals and examined for the presence of cholinergic nerves by localising choline-acetyltransferase (ChAT) containing nerves using an immunofluorescence method. The host animals had been subjected to surgical sympathectomy on the right side about one week prior to the implantation. The results provide evidence, for the first time, for the presence of cholinergic nerves on the basis of immunocytochemical localisation of ChAT positive nerves in a developing thymic rudiment in vivo. They also indicate that the presence of these nerves is associated with an increased thymic lymphopoiesis. The inter-relationship between the presence of cholinergic nerves and the maturation of thymocytes and their immunoreactivity is being further investigated.