Antidepressants like Prozac and Zoloft, which affect a brain chemical called serotonin, may also influence the body’s immune system, new research suggests.

Prozac and Zoloft belong to a group of drugs called selective serotonin reuptake inhibitors or “SSRIs,” which are thought to combat depression by causing serotonin to linger longer at nerve junctions. The new findings, which appear in the medical journal Blood, suggest that serotonin also works as a signaling molecule between certain immune cells.

Using various laboratory techniques, Dr. Gerard P. Ahern, from Georgetown University in Washington, DC, and colleagues show that serotonin is passed between two types of immune cells - dendritic cells and T cells.

The findings indicate that dendritic cells can pick up serotonin at sites of inflammation and then pass it to T cells, which influences their growth and division into new cells. Treatment with the antidepressant Prozac (fluoxetine) blocked this serotonin uptake.

Further research is needed to better understand how SSRIs might affect the immune system, the researchers note. It is possible that these drugs could one day be used to modify immune responses, they add.

SOURCE: Blood, February 1, 2006.