Medical Dangers: Antidepressants may affect human immune system.

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Source: Georgetown University Medical Center

 

http://www.sciencedaily.com/releases/2006/01/060119230939.htm

 

Commonly Used Antidepressants May Also Affect Human Immune System Drugs

that treat depression by manipulating the neurotransmitter serotonin in the

brain may also affect the user's immune system in ways that are not yet

understood, say scientists from Georgetown University Medical Center and a

Canadian research institute.

That's because the investigators found, for the first time, that serotonin is

passed between key cells in the immune system, and that the chemical is

specifically used to activate an immune response. They do not know yet, however,

whether these SSRI (selective serotonin reuptake inhibitors) drugs " including

the brands Prozac, Zoloft, Paxil and others " could have either a beneficial or a

damaging effect on human immunity.

" The wider health implication is that commonly used SSRI antidepressants,

which target the uptake of serotonin into neurons, may also impact the uptake in

immune cells, " said Gerard Ahern, Ph.D., assistant professor of Pharmacology at

Georgetown and lead researcher on the study.

He said that while it may be possible that SSRI drugs may restore a healthy

immune function in people who are depressed and prone to infections, it is

possible that they might also bolster immunity to the point that they trigger

autoimmune disease. " At this point we just don't know how these drugs might

affect immunity, so we really need to clarify the normal role of serotonin in

immune cell functioning, " Ahern said.

The surprising finding that serotonin is rapidly passed between immune cells

in a manner similar to its transmission between brain neurons was revealed in

mid-October, when the research team published the findings in the journal Blood.

In December, the discovery was highlighted for the general scientific audience

by the journal Nature Reviews Immunology, and now the research team is working

to produce an animal model that may help describe the precise nature of this

interaction.

" The novelty is that we reveal a potential communication, involving the

transmitter serotonin, between immune cells that is normally only found between

neurons, " Ahern said.

In addition to Ahern, Peta Connell, Ph.D., from the Robarts Research Institute

in Canada, was also a co-lead researcher on the study. Scientists from the

Robarts Research Institute also contributed to the work.

In the brain, serotonin transmission between neurons is associated with

feelings of pleasure, mood, and appetite, and the class of antidepressants known

as SSRIs keeps serotonin active within the synaptic spaces between neurons,

enhancing the chemical's positive effects. Unlike in the brain, which uses

chemical messengers to communicate between nerve cells, the immune system is

believed to " converse " through physical contact -- one type of immune cell

touches another, setting off a response.

Specifically, " antigen presenting cells " display their antigens (bits of a

foreign invader) to T-cells, and a resulting physical coupling between the

antigens and the T-cells will prompt the T-cells to divide and expand in

population, triggering an immune response designed to destroy the invader. This

process may take hours.

What the Georgetown researchers found, however, is that dendritic cells -- the

most powerful of the antigen-presenting cells and the ones that can find

invaders that have never infected the body and " educate " the immune system to

fight them -- also use serotonin to quickly excite a T-cell response. They

discovered that these dendritic cells can rapidly secrete serotonin, which

activates serotonin receptors on certain types of T-cells.

" In addition to the physical contact, it surprised us to find that these

immune cells also have machinery to take up serotonin and to secrete it in an

excitatory manner, " Ahern said. " The point behind this transmission is not

entirely clear, but it appears to be an additional way of stimulating a T cell

response. "

Drugs that block serotonin reuptake " likely change some of the parameters of

T-cell activation, but we don't know yet if it enhances or inhibits the total

immune response, " Ahern said. " But it is something that should be explored

because we really have no idea what SSRIs are doing to people's immune systems. "

 

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About Georgetown University Medical Center

Georgetown University Medical Center is an internationally recognized academic

medical center with a three-part mission of research, teaching and patient care

(through our partnership with MedStar Health). Our mission is carried out with a

strong emphasis on public service and a dedication to the Catholic, Jesuit

principle of cura personalis -- or " care of the whole person. " The Medical

Center includes the School of Medicine and the School of Nursing and Health

Studies, both nationally ranked, the world-renowned Lombardi Comprehensive

Cancer Center and the Biomedical Graduate Research Organization (BGRO).

 

Editor's Note: The original news release can be found here.

 

 

This story has been adapted from a news release issued by Georgetown

University Medical Center.