5′Nucleotidase and Adenosine Deaminase Activities in Human Lymphocytes and Lymphoblastoid Cell Lines
The adenosine generating enzyme 5′nucleotidase (5′N) is located on the external surface of most mammalian cells including lymphocytes1. Recent studies indicate that different lymphoid cells have widely different 5′N levels; some discrepancies appear among these data, which certainly result from different methods of 5′N determination2, but low 5′N activities were unambiguously found in lymphocytes from patients with CLL3 or hypogammaglobulinemia4 and in cord blood lymphocytes5. It was postulated that 5′N deficiency could reflect an early stage of maturation, hypothesis which is emphasized by the fact that low 5′N activities were reported for thymocytes from various species6–9. We previously demonstrated that in mouse this low level of 5′N is due to the high percentage of peanut agglutinin (PNA)-positive, hydrocortisone-sensitive thymocyte population, which represents immature cortical cells; on the contrary PNA-negative thymocytes, which are immunocompetent and represent the medullary mature population, display a 10-fold higher 5′N level than PNA+ thymocytes10. This report was conflicting with that of Barton et at 11 who found no difference in 5′N activities between rat medullary and cortical thymocytes. A recent report of Cohen et al 12, showing that 5′N activity of unseparated human thymocytes increased after incubation with factors known to induce thymocyte maturation, prompted us to verify if immature human thymocytes also lack 5′N activity like immature mouse thymocytes.
KeywordsPeripheral Blood Lymphocyte Adenosine Deaminase Burkitt Lymphoma Lymphoblastoid Cell Line Human Thymocyte
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