The mechanisms of the inhibitory effects of liver extract on lymphocyte proliferation. III. The effects of arginase on DNA polymerase activities

Inhibition of lymphocyte proliferation by liver arginase

The activities of thymidine kinase and uridine kinase (enzymes for pyrimidine salvage pathway) in phytohemagglutinin (PHA)--prestimulated lymphocytes were inhibited by arginase in a similar pattern to the inhibition on thymidine incorporation. Further study revealed that arginase did not directly affect the activities of these enzymes in the cell-free system. Thymidine kinase and uridine kinase activities of PHA-prestimulated lymphocytes were inhibited by arginase making their activities as low as that cultured in arginine-free RPMI-1640 medium. These results suggest that arginine-depletion in the culture medium is the primary mode of action of arginase on the inhibition of mitogen-stimulated lymphocyte proliferation.