GAMMA-GLUTAMYL TRANSPEPTIDASE-CELLULAR EXPRESSION IN POPULATIONS OF NORMAL HUMAN MONONUCLEAR-CELLS AND PATIENTS SUFFERING FROM LEUKEMIAS

The expression of the ectoenzyme gamma-glutamyl transpeptidase (EC2.3. 2.2, gamma GT) was investigated by flow cytometry on populations of pe ripheral blood mononuclear cells (PBMC) from healthy subjects and pati ents suffering from several types of leukemia before and under chemoth erapy. In unstimulated PBMC, 28% of these cells were found to be gamma GT positive. The highest expression was measured on monocytes (CD14/g amma GT(+) cells: 60%). Within the subsets of T lymphocytes (CD3/gamma GT(+) cells: 18%) we saw no clear differences between CD4(+) and CD8( +) cells. B lymphocytes, NK cells, and activated cells showed low expr essions (up to 10%). Treatment of PBMC with mitogens, alpha-IFN, IL-2, and GM-CSF did not affect the enzyme expression on normal mononuclear cells (MNC). However, a rapid increase of gamma GT(+) cells was found in the presence of glutathione (GSH) and n-acetyl cysteine (nAC), par ticularly on monocytes, B cells, and NK cells. Comparing 40 healthy su bjects and untreated patients suffering from leukemias, a significantl y higher expression of gamma GT(+) cells in the total MNC populations (B-CLL: 57%, CML: 62% gamma GT(+) cells) was observed in B-chronic lym phocytic leukemia (B-CLL) and chronic myelogenous leukemia (CML), wher eas other leukemias did not show clear differences. Most interestingly , the gamma GT expression was diminished in all populations of CML cel ls after 5 h of incubation in the presence of 10 units/ml IFN-alpha. T hese data suggest a possible protective role of gamma GT in MNC and a regulatory function of this enzyme in the development of CML.