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

Lymphocytes from various lymphoid organs and of 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-labeled lymphocytes was determined. The highest number of heavily labeled small lymphocytes was found in the thymus and the thoracic duct, less in peripheral blood, the lymph nodes and the spleen, and the smallest numbers in the bone marrow. A reduced ability of uridine uptake was noted in the thymectomized animals. 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 noted in bone marrow and the least in the thymus and 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-labeled lymphocytes as T cells, while unlabeled lymphocytes are considered to be B cells. The difference in uriding uptake by rat lymphocytes may serve as one of the T lymphocyte markers in a heterologous lymphoid population.