title: Distribution of terminal deoxynucleotidyl transferase and purine degradative and synthetic enzymes in subpopulations of human thymocytes.
abstract: Terminal deoxynucleotidyl transferase (TdT) and purine metabolic enzymes were examined in subsets of human infant thymocytes (defined by surface cell antigens) and normal peripheral T lymphocytes. Putative prothymocytes (RFB-1+, HTA-1+/- large blast-like cells), medium and high density cortical thymocytes (RFB-1+, HTA-1+), and medullary thymocytes (RFB-1-, HTA-1-, OKT3+) were isolated by density gradient centrifugation, monoclonal antibody and complement-mediated cytolysis, and cell-antibody affinity chromatography. Peripheral T lymphocytes were isolated from normal adult mononuclear cells using nylon fiber technique. Adenosine deaminase (ADA) and TdT were highest in prothymocytes 48.8 +/- 14.7 mumol/hr/10(8) cells (mean +/- SE) and 22.9 +/- 1.4 U/10(8) cells, respectively. Both enzymes decreased progressively down the maturation pathway. In peripheral T lymphocytes, ADA was 3.9 +/- 1.5 mumol/hr/10(8) cells, and TdT was undetectable. Purine nucleoside phosphorylase (PNP) and ecto-5'nucleotidase (5'NT) were lowest in cortical thymocytes (27.5 +/- 11.0 nmol/hr/10(6) cells and 2.8 +/- 1.3 nmol/hr/10(6) cells, respectively) and increased with T cell maturation. The PNP level was 124.9 +/- 17.2 nmol/hr/10(6) cells and 5'NT was 30.1 +/- 3.9 nmol/hr/10(6) cells in peripheral T lymphocytes. The deoxynucleoside kinases (deoxyguanosine, deoxyadenosine, and deoxycytidine kinases) paralleled the changes in ADA and TdT activity among the different T subsets. The proliferative activity (labeling index) was highest in the prothymocyte fraction and lowest in peripheral T cells. Variation in the distribution of these enzymes in T cell subsets may explain their different sensitivities to deoxyadenosine and deoxyguanosine toxicity and the different effects on T cell development of ADA or PNP deficiency.
mesh_terms: D000243:Adenosine Deaminase / Q000378:metabolism; D004253:DNA Nucleotidylexotransferase / Q000378:metabolism*; D004254:DNA Nucleotidyltransferases / Q000378:metabolism*; D006801:Humans; D009708:Nucleotidases / Q000378:metabolism; D010770:Phosphotransferases / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor); D011683:Purine-Nucleoside Phosphorylase / Q000378:metabolism; D013601:T-Lymphocytes / Q000145:classification / Q000201:enzymology*
chemical_list: D011683:Purine-Nucleoside Phosphorylase; D010770:Phosphotransferases; D017853:Phosphotransferases (Alcohol Group Acceptor); C020018:deoxyribonucleoside kinases; D004254:DNA Nucleotidyltransferases; D004253:DNA Nucleotidylexotransferase; D009708:Nucleotidases; D000243:Adenosine Deaminase