Alteration of energy substrates utilized by small and large thymocytes in resting and stimulating state

Abstract Glucose and glutamine are well known as a major energy source for proliferating rat thymocytes. Nevertheless, it is still unclear whether there is a difference in utilization of energy substrates between the mature and immature thymocytes. In the present study, we prepared small and large thymocytes from male Wistar rats by Percoll density-gradient centrifugation to answer these questions. The average diameter of the large thymocytes was approximately 1.6 times that of the small thymocytes. By flow cytometry analysis, the most of small thymocytes was immature T cells (CD4 + 8 + cells) and about 20% of the large thymocytes was CD4 + 8 − T cells. After phytohemagglutinin (PHA) and concanavalin A (ConA) stimulations in vitro , large thymocytes showed significantly higher incorporation of [ 3 H]thymidine. In contrast, small thymocytes did not exhibit a proliferative response at all. After 48 hours culture of large or small thymocytes with or without ConA stimulation, the alterations in the medium concentrations of glucose, pyruvate, lactate, ketone bodies, free fatty acids (FFA), and amino acids were analyzed. The resting large thymocytes showed significantly higher consumption of glucose and production of lactate, which were further elevated in response to ConA. In contrast, the resting small thymocytes showed slight consumption of glutamine and production of glucose. When small thymocytes were stimulated with ConA, a change to glucose consumption and lactate production was observed without an increase in either total substrate consumption or proliferative response. These results suggest that the substrates utilized by thymocytes vary from immature to mature cells and that these changes of energy substrates utilized by thymocytes are closely related to the maturation and function of thymic T lymphocytes.