A contribution to the study of lymphopoiesis in the bursa of Fabricius in Gallus domesticus.

It has been proposed that the anatomical connection between the bursa of Fabricius and the cloaca is the pathway for unknown intestinal factors which are necessary for the induction of normal bursal lymphopoiesis. It has also been suggested that normal lymphopoiesis occurs only if nerve and vascular connections are intact. Experiments were performed to test these hypotheses. To test the influence of the intestinal contents, the bursal stalk was cut on the 16th day of incubation or at hatching. In this way, contact between the bursa and the intestinal flow in embryos was avoided and bacterial contamination of the bursa at hatching was also avoided. No change in the bursal follicles was observed. To study the influence of the nervous system on bursal lymphopoiesis, the bursa was isolated from the cloaca at hatching, and by maintaining vascularization the bursa was sutured to the peritoneum of the abdominal wall after scratching the contact surfaces. Once a new vascular network was established, one fragment of bursa was completely isolated from its normal anatomical site, causing interruption of the blood vessels and nerves of the bursa. The histological appearance of the bursa was not changed. It would appear that the integrity of the anatomical relation between bursa and cloaca and an intact nerve supply is not necessary for normal lymphopoiesis to occur in the bursa of Fabricius. In contrast, sufficient vascularization appears to be essential.