Terminal deoxynucleotidyl transferase (TdT) in human foetuses. An immunofluorescent and biochemical study.

The liver, bone marrow and cord blood of 30 human foetuses between the 15th and 21st weeks of gestational age were examined. Liver suspensions were investigated both by immunofluorescent and biochemical assay; cord blood suspensions and bone marrow touches with immunofluorescent assay. The results indicate the existence of a few TdT+ cells in the liver, cord blood and bone marrow of human foetuses in the ages studied. The peaks for each organ were: 15 +/- 1.60 (mean +/- SD) TdT+ cells in the liver, 12 +/- 2 in the bone marrow and 18 +/- 2.83 in the cord blood. In all the organs TdT+ cells decrease in the later weeks. In the liver, the results of the immunofluorescent assay were confirmed by the biochemical activity.