Terminal deoxynucleotidyl transferase during the development of chicken thymus

Antibodies specific for chicken terminal deoxynucleotidyl transferase (TdT) were used to develop immunoperoxidase and immunofluorescence assays. The cellular distribution and localisation of TdT during the development of chicken thymus were studied. TdT began to appear in the embryonic thymus in the cytoplasm of large cells, between 11 and 12 days of incubation. Thereafter, the proportion of TdT-positive cells increased and TdT was detected in both nucleus and cytoplasm. The first appearance of TdT positive cells, their increasing proportion and the intracellular localisation of TdT will be discussed in correlation with the developmental stages of the thymus.