The Role of Cyclic AMP in Modulating Cytotoxic T Lymphocytes

Abstract

Cytotoxic T lymphocytes (CTL) were generated in the spleen by immunizing C57BL/6 mice (H-2^b) i.p. with allogeneic P815 cells (H-2^d), or by culturing C57BL/6 spleen cells in vitro with mitomycin C-treated P815 cells. Agents that increase cyclic AMP levels, including histamine, prostaglandin E₂, dibutyryl cyclic AMP, and theophylline, markedly inhibited the activity of in vivo-generated CTL. In contrast, these agents had little inhibitory effect on the activity of in vitro-generated CTL. The inhibition by cyclic AMP-active agents was not altered by varying lymphocyte:target cell ratios or assay times, or by removing dead cells. The differences in inhibition by histamine and dibutyryl cAMP persisted even in the presence of high concentrations of the cAMP phosphodiesterase inhibitors, theophylline and Ro 20-1724. Inhibition by mixtures of in vivo- and in vitro-generated CTL populations was the weighted average of the inhibition of each separate population. When in vivo-generated CTL were restimulated in vitro with antigen, within 24 hr, the inhibition by cAMP-active agents of the resultant CTL was no greater than inhibition of in vitro-generated, primary CTL. Thus, culture induces nonspecific desensitization of CTL to cyclic AMP-active agents, possibly by altering biochemical events in CTL such that their cytotoxic mechanism is disassociated from the cAMP-mediated regulatory step(s) that are present in in vivo populations.