Characterization of thymus - and bone marrow-derived lymphocytes in rats by means of 3H-uridine incorporation

Lymphocytes from various lymphoid oro.ans and from the thoracic duct of normal and thymectomized rats, irradiated and reconstituted with syngeneic bone marrow were tested in vitro in a minimal non-enriched cultivation medium with 3H-uridine, and the percentage of uridine-labelled lymphocytes was determined. The highest number of heavily labelled small lymphocytes was found in the thymus and in the thoracic duct, fewer in peripheral blood, the lymph nodes and the spleen, the smallest number in the bone marrow. The thymectomized animals showed reduced uridine uptake. The method of immune rosette formation was used to determine the presence of B lymphocytes in the lymphoid rat population. The highest quantity of B lymphocytes was recorded in the bone marrow and the least in the thymus and in the thoracic duct. Thymectomized animals had a significantly higher percentage of EAC rosettes than normal and sham-operated animals. The methods employed and existing literary data enabled us to identify the heavily uridine-labelled lymphocytes as T cells, while unlabelled lymphocytes are considered to be B cells. The difference in uridine uptake in rat lymphocytes may serve as one of the T lymphocyte markers in a heterologous lymphoid population. (author)