Chicken Harder's gland: evidence for a relatively pure bursa-dependent lymphoid cell population

Theophylline, caffeine, and dibutyryl cAMP, agents that elevate intracellular levels of cyclic AMP, were found to inhibit cytotoxin elaboration by PHA-stimulated human lymphocytes. Cytotoxins in diluted supernatants from 3-day lymphocyte cultures were assayed by ⁵¹Cr release from L cells. Addition of the agents to the lymphocyte cultures inhibited cytotoxin elaboration 70–90% at 10^?3M and 20–50% at 10^?5M. In addition, it was found that the inhibition is reversible and occurs at a step other than the initial mitogen triggering.The inhibition of cytotoxin elaboration by these agents correlates strikingly with their inhibition of lymphocyte-mediated target cell lysis. The results are consistent with the hypothesis that cytotoxin is the mediator of target cell killing by lymphocytes.