Mitogen-induced changes in sialyltransferase activity in human normal and leukemic lymphocytes.

Phytohemagglutinin-P (PHA-P) and concanavalin A (Con A) induced an increase in sialyltransferase (S-T) activity of the blood lymphocytes within 24 hours. PHA-P induced the maximal increase in S-T activity in the lymphocytes at 10 micrograms/ml and with Con A at 5 micrograms/ml. PHA-P induced a greater response than that by Con A. An additional effect of these mitogens was not observed. The exposure of cell extracts to these mitogens did not induce the increase in S-T activity. PHA-P or Con A had no effect on the induction of terminal deoxynucleotidyl transferase (TdT) activity, TdT-positive cells or peanut agglutinin (PNA)-positive cells from blood lymphocytes. Therefore, the change of the lymphocytes induced by these mitogens does not indicate a reversion to more immature state of lymphocyte differentiation, but represents a process of the functional differentiation to more activated lymphocytes. These mitogens had only a slight effect on S-T activity of human T-lymphoid leukemia cell lines. The decreased effects of the mitogens on S-T activity of leukemic cells may reflect the change of the membranes due to malignant transformation or the incomplete membrane structure in undifferentiated leukemic cells.