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Marijuana May Help Prevent Organ Transplant Rejection


Most of the news surrounding medical developments from marijuana are about cannabidiol (CBD), the substance that doesn’t get you high and has little, if any, palpable effect on your average user. In this field, THC, with its undesirable psychotropic properties, is usually considered the bogeyman.  Recently, though, scientists have found that THC can actually help prevent transplant rejections, albeit in mice.

Scientists first injected splenocytes from one mouse strain into the spleens of other, and found that in mice treated with THC the T-cell and cytokine profile was less inflammatory. Treating mice with THC also attenuated the rejection of a skin allograft, indicating that signaling through the cannabinoid system  could play a role in transplant rejection.  Neither of these findings are entirely remarkable, given how the immune system responds to cannabinoids.  What is surprising is that the authors claim that this immunosuppressant effect seems to occur through the CB1 receptor.  

Why this matters:  by and large, the compounds in marijuana react with two different receptors, (unimaginatively) called CB1 and CB2.  The differences between these two, physically, is quite large, actually, and if it weren’t for the fact that they both bind cannabinoids you’d be forgiven for never having thought they were related.  Both receptors are found throughout the body, but CB1 is predominant in the brain and CB2 seems to mostly found in the immune system. Most studies looking at how marijuana affects the immune system therefore focus on the CB2 receptor; the few investigations into cannabinoids and organ transplantation have found that CB2 receptors mediate the immune response..  

So if the discovery that cannabinoids can affect the immune system through the CB1 receptor is confirmed, it’s a big deal. First of all, it could mean that there may not be a way to separate some of the desired immune system effects from the undesired mental ones (unless they are desired) if they are both mediated by the same receptor.  Secondly, it means that we may have to rethink the relevance of CB1 in the immune system.  

There is no question that marijuana can affect the immune system, and in ways that are mostly for the better—at least, in the short term.  Very few things in nature are purely good or purely bad for you—and what we’re finding as we learn more and more about marijuana is that its effects are often more nuanced than we’ve realized.