The major psychoactive marijuana component, delta-9-tetrahydrocannabinol (THC), suppressed proliferation of murine spleen cells stimulated with recombinant human interleukin 2 (IL-2) and also suppressed the appearance of the lymphokine-activated killer (LAK) cell phenomenon in IL-2-treated spleen cell preparations. Cell function was depressed in a dose-dependent manner with as little as 2.5 μg/ml THC (8μM). In addition, spleen cells previously stimulated in culture with IL-2 and then incubated with THC for 4 h prior to target cell addition, displayed suppressed cytolytic activity against both YAC-1 and EL-4 tumor targets. Killing of EL 4 cells was suppressd at lower drug doses than the killing of YAC-1 targets. These results suggest that THC can suppress several important functions of IL-2 including clonal expansion of lymphocytes, expansion of killer cell populations and stimulation of killer cell cytotoxic activity.
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