THC (tetrahydrocannabinol) can suppress rodents' immune systems, according to a study at the University of South Carolina. If replicated in humans this could improve the prospects of using medical marijuana against autoimmune diseases such as arthritis, type1 diabetes and multiple sclerosis.
Despite the ceaseless ads promising that something will “boost your immune system” as an unquestioned goal, the strength of the immune response is a careful balancing act. Too weak and you are prey to a host of diseases. However, the immune system can also turn on the body itself, leading to a string of serious and sometimes fatal conditions. Finding ways to dial back the response in these cases, without opening up the floodgates to every infectious disease is one of the great challenges of modern medicine.
In the Journal of Biological Chemistry a team led by Dr Mitzi Nagarkatti reveal studies on 609 microRNAs in mice given THC. Of these, 13 showed substantial alteration. MicroRNAs regulate the expression of genes, and those affected in this case change the activation of genes associated with the immune system.
“THC mediates its activity through cannabinoid receptors (CB1 and CB2)” the authors say. “While CB1 is highly expressed in the brain, and to a lower extent in peripheral tissues, CB2 is predominant in immune cells. Therefore, besides it psychoactive effects, THC can suppress inflammation through activation of cannabinoid receptors on immune cells, using multiple pathways.”
The team's findings leave a lot of questions unanswered. Besides the question of applicability to humans, the timeframe of the effects is unclear – some are probably temporary, while others may be more permanent. However, the authors argue, “The current study opens new avenues to investigate the epigenetic pathways through which THC regulates immune response.” If the exact mechanisms through which THC affects immune response can be identified it may become possible to establish which autoimmune diseases are most likely to benefit from its use.
While some less than credible websites are keen to promote marijuana as a universal panacea, its most widely recognized medicinal uses are in treating nausea induced by chemotherapy and weight loss from AIDS. It is more widely recommended for pain and muscle spasms, but the idea of using it to treat multiple sclerosis is not new.
The researchers also have plenty of concerns about marijuana, noting “prenatal exposure to THC causes T cell dysfunction in the offspring.” They also found disturbing signs that the BRCA2 gene may be suppressed by THC. BRCA2 is famous for its association with early onset breast cancer, but this is because the BRCA2 protein normally suppresses tumor growth, and mutated versions fail to provide this protection, allowing tumors to flourish. Consequently, it is possible that suppressing BRCA2 could increase the risk of breast cancer, in contrast to research suggesting another active component in marijuana may have benefits for breast cancer.
Again, further research may help quantify this risk, and assist in working out when the increased dangers from marijuana use outweigh the benefits.
For those wondering, the THC was injected into the mice, rather than being supplied in the form of joints or hash cookies.