THYMUS CELL MATURATION : STUDIES ON THE ORIGIN OF CORTISONE-RESISTANT THYMIC LYMPHOCYTES

Outer thymic cortical large lymphocytes were labeled by transcapsular administration of tritiated thymidine. By 2–4 days after labeling, small and medium labeled lymphocyte descendants were found throughout the cortex and in the medulla. The labeled cortical lymphocytes undergo pycnosis after parenteral administration of hydrocortisone 24 h previously, but their (labeled) medullary descendants do not. In addition, parenteral administration of hydrocortisone at the time of surface labeling results in the absence of the appearance of labeled medullary descendants.