Ontogenetic Studies on Lymphoid Cell Traffic in the Chicken : III. Cell Traffic from the Thymus

• Male chickens of different ages were injected with tritiated thymidine into the parenchyma of the thymus and the transport of thymic label and of thymus-derived cells to other lymphoid organs was studied. Using a radiochemical method based on DNA and tritium measurements in different organs, a quantitatively significant transport of label from the thymus to the spleen, the caecal tonsils, and to the bone marrow could be demonstrated in the 9-day-old chicken. The transport to the spleen was shown to continue in the 6-week-old and 14-week-old animal. Autoradiographically, thymus-derived cells could be found in the spleen and caecal tonsils as early as in the newly hatched period. Autoradiographic data also indicated that the traffic increased up to 6 weeks of age but decreased in older animals. In the 6-week-old group, the localization of the thymus-derived cells in the target organs was determined. Such cells in the spleen were distributed almost equally between the red and white pulp. Very few of the thymus-derived cells were highly pyroninophilic. None could be found in the germinal centres. No sign of cell transport from the thymus to the bursa of Fabricius could be detected. The pattern of cell migration is well correlated to the morphological and functional maturation of the lymphoid system.

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