Changes in purine nucleoside phosphorylase activity during thymosin-induced human null cell differentiation.
Purine nucleoside phosphorylase (PNP) is a purine salvage pathway enzyme which we have found to be 8-10 times more active (per cell) in human peripheral blood null lymphocytes than in T lymphocytes. To test the hypothesis that null cells are, in part, pre-T lymphocytes we have defined an in vitro system for null cell differentiation into T cells and examined PNP activity during this differentiation process. We found that about 10% of human null cells could be driven to differentiate into T cells using thymosin fraction 5 (TF5) an extract of bovine thymus glands. The response to TF5 was dose related to up to 250 micrograms/ml with a maximum response occurring by 42-46 hr incubation. Exposure to TF5 was necessary for more than 4 hr but no more than 8 hr in order to obtain a maximum response. Both OKT4 and OKT8 positive cells were present in the newly differentiated T cell population but OKT8 positive cells appeared to predominate (OKT4/OKT8 = 0.698 +/- 0.30, mean +/- 1 SD). The differentiation process did not involve DNA synthesis but was inhibited at 4 degrees C. In the newly differentiated T cells PNP activity per cell was 8- to 10-fold lower (36 +/- 23 nm/hr/106 cells) than in null cells (311 +/- 136), and was at a level similar to mature T cells (56 +/- 7). Thus, human peripheral blood null cells can be induced to differentiate into T lymphocytes which can be characterized by both surface markers and biochemical parameters. Future studies will look at the function of TF5-induced T cells and the regulation of PNP activity during the differentiation process.
D000328:Adult; D002454:Cell Differentiation; D004247:DNA / Q000096:biosynthesis; D006801:Humans; D007700:Kinetics; D008215:Lymphocytes, Null / Q000166:cytology / Q000201:enzymology*; D010430:Pentosyltransferases / Q000097:blood*; D011683:Purine-Nucleoside Phosphorylase / Q000097:blood*; D013601:T-Lymphocytes / Q000145:classification / Q000166:cytology / Q000201:enzymology; D013696:Temperature; D013947:Thymosin / Q000031:analogs & derivatives / Q000494:pharmacology*; D013951:Thymus Hormones / Q000494:pharmacology*
D013951:Thymus Hormones; C033782:thymosin fraction 5; D013947:Thymosin; D004247:DNA; D010430:Pentosyltransferases; D011683:Purine-Nucleoside Phosphorylase