Marijuana and immunity: tetrahydrocannabinol mediated inhibition of lymphocyte blastogenesis.

The effects of delta-9-tetrahydrocannabinol (THC) and its major metabolite, 11-OH delta-9-tetrahydrocannabinol (11-OH THC) on mitogen driven lymphocyte blastogenic transformation (LBT) were studied. THC inhibited LBT responses to the T lymphocyte mitogens phytohemagglutinin and concanavalin A but not the B lymphocyte stimulant pokeweed mitogen. The metabolite 11-OH THC caused a comparable, but less significant, inhibition of LBT responses to the T cell mitogens. These inhibitions were dependent upon the drug doses and the time of incubation with the lymphocytes. There was no significant inhibitory activity of THC to the LBT when it was added 24 or 48 h after mitogen. In addition, exposure of lymphocytes to THC for 3 h, followed by removal of the drug prior to addition of mitogen had no effect on the cells' ability to respond to the mitogen. Thus, there appears to be a specified temporal period during which exposure of lymphocytes to THC results in an inhibition of blastogenesis. Interleukin 2 (30 units/ml) could not preclude the THC induced inhibition of lymphocyte blastogenesis. We conclude that THC and 11-OH THC inhibit T lymphocyte blastogenesis. However, unlike the THC mediated inhibition of natural killer cell activity (as shown previously), the process is not responsive to the cytokine interleukin 2.