A new study, involving an Indian-origin boffin, has explained how cannabis dampens the body's immune system.
Cannabis is a double-edged sword: by dampening the immune system, it provides relief from inflammatory diseases, but also increases the risk of infections.
Now, scientists have found that its active ingredient targets a newly discovered type of cell that lowers the immune response.
Prakash Nagarkatti at the University of South Carolina School of Medicine and colleagues injected the main active ingredient of cannabis, delta-9-tetrahydrocannabinol (THC), into mice, reports New Scientist.
THC activated two types of cannabinoid receptor on immune cells, called CB1 and CB2. Activation of these receptors led to a "massive mobilisation" of myeloid-derived suppressor cells (MDSCs), which play a crucial role in lowering the immune system response back down to normal levels.
The discovery offers a possible explanation of why cannabis smokers have a higher risk of getting infections, says Nagarkatti.
It may also mean THC could be used when there is a need to suppress the immune system - after an organ transplant, for example.
The study appears in the European Journal of Immunology.