Marijuana and the Cannabinoids

Effects of Marijuana on Immune Defenses 267
Fig. 4. Tetrahydrocannabinol (THC) shifts the capacity for activated T-cells to produce
T-helper type 1 (Th1) and T-helper type 2I (Th2) cytokines. Purified human T-
cells were activated with a combination of monoclonal antibodies directed against
the T-cell receptor (CD3) and costimulatory molecules (CD28) in the presence of
control medium (left panel) or medium supplemented with interleukin (IL)-12 (10 ng/mL,
middle panel) or THC (5 µg/mL, right panel). Cells were permeabilized, and the
production of interferon (IFN)-γ, a Th1 cytokine, and IL-4, a Th2 cytokine, was
detected in each cell by flow cytometry. IL-12 increased the Th1/Th2 ratio, whereas
THC decreased the production of IFN-γ and the Th1/Th2 ratio.
balance similar to that observed in animal models (44,74,75). When examined at the
single cell level, THC decreased both the number of T-cells producing IFN-γ and the
average cytokine production per cell (Fig. 4). CD4 + and CD8 + T-cells were both equally
suppressed. The impact of THC on the subsets was also examined at the level of mRNA
expression using a ribonuclease protection assay to simultaneously assay for both Th1
(IL-2, IFN-γ) and Th2 (IL-4, IL-5) cytokines. Consistent with the results obtained by
enzyme-linked immunosorbent assay and single cell analyses, mRNA encoding for
IFN-γ and IL-2 was reduced by 21–48% in cells treated with 5 µg/mL THC, and mRNA
encoding for IL-4 and IL-5 was increased by 1.5- to 11.2-fold. Pretreatment with
SR144528, a CB 2 -selective antagonist, prevented the majority of the THC-mediated
effects, whereas there was little response to AM251, a selective CB 1 antagonist. This
work suggests a strong correlation between murine models and human studies, with
THC acting via cannabinoid receptors to suppress antigen-specific T-cell activation
and skew responding T-cells toward a Th2 profile (86).
As in the mouse model by Zhu et al. (44), THC also upregulates the production
of TGF-β when human T-cells are activated by immobilized anti-CD3 (68). TGF-β,
although not a classic Th2 cytokine, inhibits T-cell proliferation, suppresses production
of IL-2 and IFN-γ, and antagonizes the activation of both lymphocytes and monocytes.
As little as 50 ng/mL of THC increased the production of TGF-β two- to threefold,
and 5 µg/mL of THC increased the release of TGF-β protein fivefold. To evaluate the
role of cannabinoid receptors in this response, human T-cells were pretreated with
either pertussis toxin, forskolin, or methylxanthine before activation in the presence
of THC. Inactivation of G protein-coupled receptors by pertussis toxin, activation of
adenyl cyclase by forskolin, and inactivation of phosphodiesterase activity by