Effect of thymic humoral factor on intracellular levels of cyclic AMP in human peripheral blood lymphocytes.

The exposure of human peripheral blood lymphocytes to thymus hormone causes an increase in the intracellular cyclic AMP level in these cells. Studies of the thymus-hormone-induced changes in cellular cyclic AMP levels revealed that cord blood lymphocytes contain significantly more target cells for the hormone than adult peripheral blood lymphocytes. The data obtained also suggest that the interaction between the hormone and its target cell is not readily reversible and that only a certain proportion of target cells in a given population of lymphocytes can be activated by a constant and limited amount of thymus humoral factor.