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[mb12 valtrex] MED,RES:Antidepressants May Also Affect Immune System

Source: town University Medical Center

Date: 2006-01-20

URL: 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 town

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 town 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 town 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. "

###

About town University Medical Center

town 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).

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