The negative effects of marijuana on teenagers' brain development have come into sharper focus lately; now, a study in the European Journal of Immunology shows how cannabis can adversely affect the immune system. Dr. Prakash Nagarkatti of the University of South Carolina led a team of immunologists who found that marijuana consumption can leave the body open to a host of serious diseases, including cancer. Here's a brief guide to Dr. Nagarkatti's findings:

What's the central conclusion?

Nagarkatti found that chemicals in cannabis, including its psychoactive ingredient THC, may lead to an increasingly vulnerable immune system. His team found that marijuana activates a group called myeloid-derived suppressor cells, or MDSCs. These cells often act as a "safety brake" on the immune system by ensuring that it does not go too far in fighting a disease. But in the case of cancer patients, MDSCs over-multiply, leaving the immune system weakened. Marijuana consumption mimics this response, Nagarkatti discovered, leaving the body more open to pneumonia, cancerous tumors, and bacterial infections like Legionnaire's disease.

Is this all bad news?

Not necessarily. Even though a surplus of MDSCs can lead to infections, says Nagarkatti, "further research of these compounds could provide opportunities to treat a large number of clinical disorders where suppressing the immune response is actually beneficial."

Is this a definitive link?

It has not yet been established definitively, since it is unclear whether trials on mice will translate into human results. Says Henry Scowcroft of Cancer Research UK: "The issue of whether cannabis can cause cancer is a controversial one that is still not settled."

Sources: The Daily Mail, eMaxHealth