Suppression of lymphocyte adenosine 3':5'-cyclic monophosphate (cAMP) by delta-9-tetrahydrocannabinol.

Delta-9-tetrahydrocannabinol (THC) is the major psychoactive component of marijuana. Suppression of mitogen-stimulated blastogenesis of human lymphocytes in vitro by THC was previously demonstrated. This effect was shown to be concentration dependent with the non-toxic concentrations 5, 7.5, and 10 micrograms THC/ml showing the greatest suppression. However, the mechanism(s) by which THC induces suppression are still unclear. The current study examines the effect of THC on the adenosine 3':5'-cyclic monophosphate (cAMP) pathway second messenger system, which is involved in activation of human peripheral blood lymphocytes. Lymphocyte cAMP levels were stimulated using three hormone receptor stimulators, isoproterenol, histamine, or 5'-N-ethylcarboxamide adenosine (NECA), each of which utilizes a different receptor to enhance cAMP production. THC suppressed cAMP levels independently of the hormone and receptor utilized. Levels of cAMP in non-mitogen-stimulated peripheral blood mononuclear cells and plastic non-adherent lymphocytes, as well as cells stimulated with phytohemmagglutinin, were suppressed by THC. Suppression of cAMP production by THC was further examined to determine whether inhibition involved a GTP-binding protein (Gi), which is known to down-regulate cAMP production. Cells were pre-treated with pertussis toxin to inhibit Gi activity; this blocked the THC-induced suppression of cAMP production. These results suggest that THC can exert its effects on second messenger systems at the lymphocyte membrane level, and that a pertussis toxin-sensitive Gi protein may be involved. Thus, second messenger regulated pathways may be involved in THC-induced immune suppression. However, the relationship between alteration of cAMP production and suppression of lymphocyte function due to the presence of THC in the medium remains to be established.