Lymphocyte activation: The dualistic effect of cAMP

The effects of exogenously added cyclic nucleotides on DNA synthesis have been investigated in human peripheral blood lymphocytes stimulated with phytohemagglutinin (PHA). At low doses of PHA the addition of exogenous cAMP resulted in an inhibition of DNA synthesis. At optimal or supraoptimal doses of PHA the addition of cAMP, db-cAMP, or 8-Br-cGMP resulted in enhancement of DNA synthesis. Measurement of cell associated cAMP and cGMP levels in lymphocytes exposed to PHA with or without exogenously added cAMP revealed a gradual increase in cAMP levels and a fluctuating decline in cGMP levels.