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Stress hormones moonlight as immune-system traffic cops

Stress hormones moonlight as immune-system traffic cops

Birds do it. Bees do it. Even fishies in the seas do it. They freak out when put into stress-arousing situations. A hormone-induced call-to-arms called the flight-or-fight response quickens the senses, douses pain sensation, and pumps mammalian muscles to full strength.

Short-term stress not only energizes muscles but mobilizes immune cells, a just-published paper in the journal Psychoneuroendocrinology, spearheaded by Stanford’s Firdaus Dhabhar, PhD, shows. And that’s a good thing.

I know, I know. As I wrote in my press release on this development:

You’ve heard it a thousand times: Stress is bad for you. And it’s certainly true that chronic stress, lasting weeks and months, has deleterious effects including, notably, suppression of the immune response.

But short-term stress, a mobilization of bodily resources lasting minutes or hours in response to immediate threats, stimulates immune activity.

Dhabhar gently confined rats inside amply ventilated Plexiglas enclosures, inducing mild stress. (Think: “office cubies.”) Then he meticulously plotted the paths of several key immune-cell types. These cells responded like combat troops to squirts of three major stress hormones released from the rats’ adrenal glands on orders from the brain. First, they spilled out of their rest-and-recuperation reservoirs, the spleen and bone marrow, to the boulevard that is the bloodstream. Then – depending on the identities, timing and amounts of the stress hormones secreted - different immune-cell subsets parachuted out of circulation into potential front-line battle zones such as the skin and mucous membranes.

Which makes evolutionary sense, says Dhabhar. The immune system is crucial for wound healing and preventing or fending off infections, common risks during chases, escapes, and combat. “Mother Nature gave us the fight-or-flight site stress response to help us, not to kill us,” he says.

Dhabhar’s study caps over a decade of research into how the the brain manipulates the immune system with the aid of stress hormones. A few years ago he found that knee-surgery patients recovered faster and better if, during surgery, their immune-cell populations redistributed similarly to the pattern seen in the healthy rats in this new study. If those cells merely flatlined in response to the inevitable stress-hormone storm released during surgery, outcomes were poorer. (The latter pattern resembles what happens under conditions of chronic stress: a new bout of stress-hormone secretion just evokes a collective yawn from the body’s immune-cell army, which has been on alert so long it’s starting to sleep on the job.)

Imagine if this mechanism evolution built into us to help us get out of jams in the wild were domesticated. Dhabhar foresees a day when patients’ stress-hormone and immune status could be monitored before surgery or just prior to vaccination, and then precise, precisely timed doses of specific stress hormones could be given to optimize immune responsiveness. Conversely, crucial immune cells could be hormonally directed to hole up in safe havens such as the spleen while a cancer patient was getting chemotherapy or radiation, or to quiet down in a patient with an autoimmune disorder.

(The more quotidian takeaway: Life’s little stresses benefit your health. Just make sure to exhale.)

Photo by spaceamoeba

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