Adenosine deaminase activity in thymus and other human tissues

Adenosine deaminase activity (ADA) has been estimated in human tissues. Levels in the thymus during childhood were very much higher than in any of the other 6 tissues studied. Intermediate activities were obtained from spleen and lymph nodes and also skin. Cerebral cortex, liver and kidney had relatively low levels. ADA activity in lymphocytes from peripheral blood was significantly increased after antigenic stimulation by TAB immunization. The available evidence appears to be consistent with T-lymphocyte growth and development in the thymus being dependant on ADA.