In the Journal of Neuroimmune Pharmacology in July 2013, lead author and Temple University School of Medicine Researcher Rebecca Hartzell Robinson writes that THC, the stuff on weed that causes euphoria, also helps with immunosuppression during organ transplants.
In the abstract for the paper, "Cannabinoids Inhibit T-cells via Cannabinoid Receptor 2 in an In Vitro Assay for Graft Rejection, the Mixed Lymphocyte Reaction" the authors write THC and other pot compounds - "cannabinoids" - "are known to have anti-inflammatory and immunomodulatory properties."
So the researchers doped mouse immune cells "leukocytes" with Δ9-tetrahydrocannabinol (Δ9-THC) to see if the molecule inhibits the murine Mixed Lymphocyte Reaction (MLR), which is "an in vitro correlate of graft rejection following skin and organ transplantation."
"Δ9-THC significantly suppressed the MLR in a dose dependent fashion," researchers write. "These data support the potential of this class of compounds as useful therapies to prolong graft survival in transplant patients."
THC binds to a receptor site on human and mouse leukocytes known as the CB2, where it's been shown to modulate - often beneficially - immune cell reactions to bodily injury, disease and grafted organs. Researchers in 2009 wrote:
"It is becoming increasingly clear that cannabinoid receptors and their endogenous ligands play a crucial role in the regulation of the immune system. Exogenous cannabinoids have been shown to suppress T-cell-mediated immune responses by primarily inducing apoptosis and suppressing inflammatory cytokines and chemokines. Such observations indicate that targeting cannabinoid receptor–ligand interactions may constitute a novel window of opportunity to treat inflammatory and autoimmune disorders. As CB2 receptors are primarily expressed on immune cells, targeting CB2 may result in selective immunomodulation without overt toxicity."