γ-Glutamyl transpeptidase-cellular expression in populations of normal human mononuclear cells and patients suffering from leukemias

Abstract

The expression of the ectoenzymeγ-glutamyl transpeptidase (EC2.3.2.2.,γGT) was investigated by flow cytometry on populations of peripheral blood mononuclear cells (PBMC) from healthy subjects and patients suffering from several types of leukemia before and under chemotherapy. In unstimulated PBMC, 28% of these cells were found to beγGT positive. The highest expression was measured on monocytes (CD14/γGT⁺ cells: 60%). Within the subsets of T lymphocytes (CD3/γGT⁺ cells: 18%) we saw no clear differences between CD4⁺ and CD8⁺ cells. B lymphocytes, NK cells, and activated cells showed low expressions (up to 10%). Treatment of PBMC with mitogens, α-IFN, IL-2, and GM-CSF did not affect the enzyme expression on normal mononuclear cells (MNC). However, a rapid increase of yGT⁺ cells was found in the presence of glutathione (GSH) and n-acetyl cysteine (nAC), particularly on monocytes, B cells, and NK cells. Comparing 40 healthy subjects and untreated patients suffering from leukemias, a significantly higher expression ofγGT⁺ cells in the total MNC populations (B-CLL: 57%, CML: 62%γGT⁺ cells) was observed in B-chronic lymphocytic leukemia (B-CLL) and chronic myelogenous leukemia (CML), whereas other leukemias did not show clear differences. Most interestingly, theγGT expression was diminished in all populations of CML cells after 5 h of incubation in the presence of 10 units/ml IFN-α. These data suggest a possible protective role ofγGT in MNC and a regulatory function of this enzyme in the development of CML.