Early exposure to tetrahydrocannabinol (THC), the main active component of marijuana, can affect immune system development, leading to immune-related diseases in adulthood.

Italian researchers found that using marijuana in adolescence may do serious long-term damage to the immune system. This damage may result in autoimmune diseases and chronic inflammatory diseases, such as multiple sclerosis, inflammatory bowel disease and rheumatoid arthritis in adulthood.

"I hope that the knowledge that early exposure to marijuana is associated with immediate and long-term deleterious effects on the immune system may reach adolescents and their families," Paola Sacerdote,., a researcher involved in the work from the Università degli Studi di Milano in Milano, Italy, said in a statement. "The increased risk of getting sick in adulthood may hopefully be a deterrent for marijuana abuse among young individuals."

For the study, scientists injected "adolescent" mice with THC for 10 days. This period in the mouse lifecycle corresponded to the adolescence period in humans (approximately ages 12-18). A second group of adolescent mice received only a placebo.

At the end of treatments, both groups of animals were left undisturbed for approximately two months, until they reached full adulthood. The activity of the immune system was then evaluated, taking into consideration several important measurements, such as the ability of leukocytes to produce cytokines to mount an antibody response to vaccination or the capacity of macrophage to phagocyte particles.

They found that the group of mice treated with THC in adolescence had severe alterations of immune responses in adulthood, characterized by a clear switch toward a pro-inflammatory and cytotoxic phenotype.

"These studies not only point to adolescence as a key phase of immune system sensitivity, but also highly the dramatic and long-lasting negative effects that a common recreational drug abused by teenagers may have on immune function," said John Wherry, deputy editor of the Journal of Leukocyte Biology.

The findings were published in the October 2014 issue of the Journal of Leukocyte Biology.