Abstract

5'-Nucleotidase (5'N) activity, which is present in lymphocytes isolated from the blood of normal subjects, is markedly diminished or not detectable in most patients with chronic lymphocytic leukemia (CLL). The relation to lymphocyte subpopulations and the effect of mitogenic stimulation and disease states on 5'N were investigated. The reduced activity in CLL does not stem from the increase in the percentage of B-lymphocytes found in this disorder. Stimulation of normal or 5'N-positive CLL lymphocytes with phytohemagglutinin does not lead to a decrease in activity comparable to that found in 5'N-deficient CLL cells. In contrast to what was observed with 5'N, the level of another plasma membrane marker enzyme, diphosphopyridine nucleotide diaphorase, is normal in CLL. In lymphocytes from 103 patients with a wide variety of clinical disorders, normal levels were found in all cases except during the early phase of infectious mononucleosis, when a marked decrease occurred. In certain patients with CLL the decreased enzyme level has remained constant over more than 24 months of observation; the decreased activity in infectious mononucleosis is, on the contrary, a very transient finding, with a gradual return to normal levels. The lymphoblasts isolated from the blood in 2 out of 5 patients with acute myeloblastic leukemia studied had markedly decreased 5'N activity. It appears that lymphocyte 5' activity may be useful in the biochemical characterization of subgroups of patients with lymphoid leukemias. 1 This work was supported by NIH Grants CA 11655 and AM 01431. 2 Scholar of the Leukemia Society of America.