γ Glutamyl transpeptidase, a lymphoid cell surface marker: relationship to blastogenesis, differentiation, and neoplasia
gamma-Glutamyl transpeptidase, an enzyme that catalyzes gamma-glutamyl transfer from gamma-glutamyl compounds to amino acid and peptide acceptors, and which is known to be localized in the membranes of many epithelial cells, was found in a variety of lymphoid cells. The lymphoid cell enzyme is located on the cell surface, and exhibits substantially the same substrate specificity as the enzyme found in epithelial cells. Human and rat (but not mouse) lymphocyte gamma-glutamyl transpeptidase was stimulated by treatment of the cells with mitogens. Normal human peripheral B-cells were more active than T-cells, but the reverse relationship of activities was found in chronic lymphocytic leukemia lymphocytes. Human lymphoblastic lines vary markedly in activity. In general, cell lines with B- and T-characteristics from patients with lymphoproliferative diseases had much lower activities than those of B-cell lines derived from normal subjects. The highest activity found was in a human myeloma line active in synthesis of an immunoglobulin light chain. The data indicate that gamma-glutamyl transpeptidase is a surface marker reflecting differentiation in normal and neoplastic cells.