Popular Antidepressants May Also Affect Human Immune System

[Guest guest]

Popular Antidepressants May Also Affect Human Immune System

http://www.medicalnewstoday.com/medicalnews.php?newsid=36441

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. "