Effect of thymosin and lipopolysaccharide on murine lymphocyte cyclic AMP

The effects of thymosin and lipopolysaccharide (LPS) on cyclic AMP levels in lymphocytes were evaluated using three independent assays which included adenine prelabeling, protein kinase binding, and radioimmunoassay. All three assays proved to be both sensitive and accurate in assessing relative changes in lymphocytes after incubation in vitro with various agents. The assays confirmed that basal and stimulated levels of cyclic AMP depended on the origin of the lymphocyte population. Each of the three techniques demonstrated that pyrogen-free bovine thymosin fraction 5 did not elevate thymocyte cAMP levels. In contrast, it was found that lipopolysaccharide (lps) significantly elevated cAMP levels in both spleen and thymus lymphocytes. These studies indicate that assays for measuring the activity of thymic extracts in which the intracellular levels of cyclic nucleotides are a criterion for activity are only valid if the preparations are not contaminated with endotoxins.