Morphologic and Autoradiographic Observations of H³-Thymidine-Labeled Thoracic Duct Lymphocytes Cultured in Vivo

1. The behavior of mouse and rat thoracic duct lymphocytes cultivated in diffusion chambers implanted into the peritoneal cavity of recipient mice and rats has been described.

2. The temporal pattern of labeling of cultured thoracic duct lymphocytes labeled with H³-thymidine has been described. From an analysis of this pattern and the changes in the mean grain count of the different classes of lymphocytes a maximum generation time for large and medium lymphocytes of 15 and 24 hours has been calculated. The results of these experiments favor an origin of small lymphocytes from the division of large and medium lymphocytes.

3. Some evidence for the transformation of thoracic duct lymph cells into monocytoid cells was found. In homologous cultures of labeled thoracic duct lymph cells and unlabeled bone marrow apparent evidence for transformation of labeled cells into plasma cells was found. The data suggest that neither the monocytoid cells nor the plasma cells arose necessarily from small lymphocytes. It was concluded that some unidentified cells, presumably the largest cells which are normally present in thoracic duct lymph, can be transformed into these other cell types when appropriately stimulated.