Search

PERIPHERAL blood lymphocytes in culture undergo cell division in the presence of the mitogenic stimulant phyto-haemagglutinin (PHA)1. Some of the metabolic processes that occur shortly after stimulation include phosphorylation of membrane bound phosphatidyl inositol2, acetylation of histones3, changes in cyclic GMP levels4, a pronounced elevation of uridine kinase activity5 and increases in RNA synthesis6 and protein synthesis7. These events are followed by the initiation of DNA replication within approximately 24 h8,9. Frequently, labelled uridine and thymidine are used as nucleic acid precursors to measure RNA and DNA biosynthesis. In one of these studies, Lucas observed that additions of cytidine inhibited the incorporation of labelled uridine into RNA in PHA-stimulated lymphocytes5. This finding was confirmed in this laboratory and these studies were expanded to include the effects of other nucleosides such as guanosine on lymphocytes from healthy donors and from patients with chronic lymphocytic leukaemia (CLL)10.

Lymphocytoid and plasmacytoid blasts have been identified in both normal and chronic lymphocytic leukemia lymphocyte cultures exposed to NaIO4. However, the appearance of ultrastructurally abnormal blasts in chronic lymphocytic leukemia cultures suggests that NaIO4 also stimulates the transformation of an abnormal subpopulation of lymphocytes. Development of invaginated nuclei produced morphological features similar to nuclear blebs, a cellular abnormally described in blood cells from other cancers. Furthermore, the consistent localization of nuclear invagination only to portions of nuclei adjacent to developing cytoplasmic microtublar complexes suggests a role for microtubules in the transformation process. The absence of these unusual blasts in cultures stimulated with other mitogens may indicate that these NaIO4-sensitive cells are not responsive to the more commonly used plant lectins.

The role of cyclic adenosine 3':5'-monophosphate (cyclic 3':5'-AMP) in the regulation of cell division in lymphocytes obtained from healthy donors and from patients with chronic lymphocytic leukemia (CLL) was investigated by determining the levels of cyclic 3':5'-AMP and glycogen and also the activities of several enzymes that are closely associated with the metabolism of these cellular components. Intracellular levels of cyclic 3':5'-AMP were measured in normal and CLL lymphocytes in nondividing, dividing, and quiescent [after phytohemagglutinin (PHA) addition]states. In normal lymphocytes the levels of cyclic 3':5'-AMP fluctuated throughout the cell cycle after PHA addition, whereas in CLL lymphocytes the levels were approximately 3-fold lower than in normal cells and remained relatively constant before, during, and after mitogenic stimulation. Normal cells contained approximately 3-fold lower levels of glycogen than CLL cells, whereas glycogen phosphorylase activities were increased 2- to 4-fold above those in nondividing cells in normal but not in CLL lymphocytes after stimulation with PHA. Furthermore, cyclic 3':5'-AMP phosphodiesterase activities were higher in CLL lymphocytes than in normal ones. Collectively, these studies demonstrated that (a) the intracellular levels of cyclic 3':5'-AMP differ in these two cell types; (b) the levels of cyclic 3':5'-AMP and glycogen qualitatively correlate with the activities of the enzymes that are related to these components; and (c) an inverse relationship between the levels of cyclic 3':5'-AMP and cell growth exists in mitogen-stimulated lymphocytes from healthy donors but not from patients with CLL. These biochemical differences are presumed to exist between normal and "leukemic" lymphocytes, but alternatively they may reflect normal populations of immunologically distinct lymphocytes.