How Cannabis Suppresses Immune Functions: Cannabis Compounds Found to Trigger Unique Immune Cells Which Promote Cancer Growth
ScienceDaily (Nov. 26, 2010)
— An international team of immunologists studying the effects of
cannabis have discovered how smoking marijuana can trigger a
suppression of the body’s immune functions. The research, published in
the European Journal of Immunology, reveals why cannabis users are more susceptible to certain types of cancers and infections.
The team, led by Dr Prakash Nagarkatti from the University of South
Carolina, focused their research on cannabinoids, a group of compounds
found inside the cannabis plant, including THC (delta-9
tetahydrocannabinol) which is already used for medical purposes such as
“Cannabis is one of the most widely used drugs of abuse worldwide
and it is already believed to suppress immune functions making the user
more susceptible to infections and some types of cancer,” said Dr
Nagarkatti. “We believe the key to this suppression is a unique type of
immune cell, which has only recently been identified by immunologists,
called myeloid-derived suppressor cells, MDSCs.”
While most immune cells fight against infections and cancers to
protect the host, MDSCs actively suppress the immune system. The
presence of these cells is known to increase in cancer patients and it
is believed that MDSCs may suppress the immune system against cancer
therapy, actually promoting cancer growth.
Dr Nagarkatti’s team demonstrated that cannabinoids can trigger a
massive number of MDSCs through activation of cannabinoid receptors.
This research reveals, for the first time, that marijuana cannabinoids
may suppress the immune system by activating these unique cells.
“These results raise interesting questions on whether increased
susceptibility to certain types of cancers or infections caused from
smoking marijuana results from induction of MDSCs,” said Nagarkatti.
“MDSCs seem to be unique and important cells that may be triggered by
inappropriate production of certain growth factors by cancer cells or
other chemical agents such as cannabinoids, which lead to a suppression
of the immune system’s response.”
In a related study, also published in the European journal of
Immunology, Dr Christian Vosshenrich from the Institut Pasteur in
Paris, reveals that when cancer cells grow they produce a molecule
called interleukin-1 β (IL-1β), which also triggers MDSCs. This study
identifies how MDSCs produced during cancer growth also weaken the
ability of immune cells to kill cancer cells.
“Marijuana cannabinoids present us with a double edged sword,”
concluded Dr Nagarkatti. “On one hand, due to their immunosuppressive
nature, they can cause increased susceptibility to cancer and
infections. However, further research of these compounds could provide
opportunities to treat a large number of clinical disorders where
suppressing the immune response is actually beneficial.”