Morphine-Induced Immunosuppression, From Brain to Spleen

RESEARCH FINDINGS

Morphine-Induced Immunosuppression, From Brain to Spleen

Morphine sets off a chain of biological events that stifles the immune response.

BY LORI WHITTEN, NIDA Notes Staff Writer

M

orphine and other opioids suppress the immune sys- tem, the body's innate defense against infections. Because of this effect, doctors weigh the pain-relief benefits of opioids against the added risk of infection they pose to patients, particularly those being treated for severe burns or certain cancers. Opioid abusers, many of whom are already infection-prone due to unclean needles, repeated injections, and poor nutrition and living conditions, are rendered even more vulnerable by these drugs.

Morphine affects the body's immune cells in many ways, both direct and indirect. Recently, NIDA-funded scientists pinpointed the biochemical trigger that sets off a chain reaction that ultimately inhibits an immune cell that is key in fighting viruses and cancer. If validated in future studies, the work could lead to interventions to bolster the immunity of those who regularly take opioids.

MORPHINE, DOPAMINE, AND

NATURAL KILLERS

Morphine suppresses the activity of three different types of white blood cells: T lymphocytes, B lymphocytes, and natural killer (NK) cells (see box). NIDA-funded investigators Dr. Donald Lysle, Dr. Timothy Saurer, and their colleagues at the Universi- ty of North Carolina (UNC), Chapel Hill, concentrated on NK cells, and found that

morphine-induced immunosuppres- sion follows activation of dopamine-1 (D) receptors in the shell of the nucleus accumbens (NAc); and

a train of biochemical events links stim- ulation of these D, receptors with reduced NK cell activity in the spleen. In previous studies, the UNC team had established that blocking one of mor- phine's pharmacological effects in the brain-a surge of dopamine into the NAC- averts suppression of NK cells in the spleen. This being the case, the researchers reasoned that morphine-induced NK sup- pression must start with something that dopamine does in the NAc.

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