The Fate of Thymocytes: A Study of Kinetics of Thymocytes using High Alkaline Phosphatase Activity as an Endogenous Label

Abstract

The high activity of alkaline phosphatase (AP) in the guinea pig cortical thymocytes offers a new, easily demonstrable endogenous label for these cells. In this study observations were made on the frequency of AP‐positive lymphocytes occurring spontaneously in blood and lymphatic organs and on the fate of xenogeneic, allogeneic and autologous thymocytes injected intravenously. In the guinea pig blood on the average 0.4 % of white cells are AP‐positive lymphocytes. In the lymph nodes about one in every hundred lymphocytes shows high AP‐activity, the corresponding frequency in the spleen being 1/1000 white cells. No significant difference was found between the frequencies of AP‐positive lymphocytes in the thymic and other venous blood. After intravenous injections xenogeneic, allogeneic and autologous thymocytes disappeared very rapidly from the blood and never returned into the circulation. Previous thymectomy did not affect the disappearance rate of thymocytes. A significant part of the cells injected was found in the spleen, bone marrow and lymph nodes. Our results are in favour of a theory that relatively few cortical thymocytes as such leave the thymus and those leaving are rapidly gathered in the spleen and lymph nodes. Lymphocytes directly deriving from the thymus (cortex) are no regular constituents of the blood white cell population.