Adolescent exposure to THC may cause immune systems to go up in smoke

"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," said Paola Sacerdote, Ph.D., a researcher involved in the work from the Università degli Studi di Milano in Milano, Italy. "The increased risk of getting sick in adulthood may hopefully be a deterrent for marijuana abuse among young individuals."

To make this discovery, scientists injected "adolescent" mice with THC, the main active component of marijuana, 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. 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.

"The immune system is characterized by an impressive ability to 'remember' previous exposures and changes during the period of immune system development especially early in life can have important long-term consequences," said John Wherry, Ph.D., Deputy Editor of the Journal of Leukocyte Biology. "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."