Terminal deoxynucleotidyl transferase development in the postnatal human thymus.

Terminal deoxynucleotidyl transferase activity was studied in 42 whole human thymuses of different ages (2 days to 70 years). The results indicate that enzyme activity is high perinatally, falls soon after birth, rises to maximal activity early in life, and falls thereafter. Enzyme activity in homologous thymocytes of 9 thymuses ranging from 2 days to 105 months was also determined. The relative enzyme activity (thymocyte/thymus) did not remain constant with age. These results suggest that age-related changes in thymus terminal transferase activity occur which do not reflect a simple coordinate regulation of thymocyte and non-thymocyte elements.