Feedback Mechanisms of Thymic Lymphocyte Production.

Summary Thymidine-H3 uptake of thymocytes from rats injected with antilymphocyte serum was increased when the blood lymphocyte count was low whereas it was decreased when the count returned to normal. Thymocytes from rats injected with antithymus serum showed increased RNA metabolism despite lowered thymidine-H3 uptake and sustained lymphopenia. The increased RNA metabolism may indicate a compensatory increase in the production of a thymic humoral factor which was inactivated by antithymus serum in the blood resulting in sustained lymphopenia.