June 5, 2019

It’s proven stress wears down the body and compromises the immune system—but why?

Scientists can’t yet fully explain how the association between stress and health plays out at the cellular level, but they are closer thanks to recent results from a collaborative study. Researchers at the Washington National Primate Research Center (WaNPRC) at the University of Washington (UW) in collaboration with researchers at Duke University, the University of Montreal and the Yerkes National Primate Research Center (YNPRC) at Emory University examined the cellular effects of one common stressor: social hierarchy.

“The goal is to understand the mechanisms through which social experiences or environment ‘get under the skin,’ so to speak, to affect health and survival,” said the study’s lead author, Noah Snyder-Mackler, a UW assistant professor of psychology.

In the study, scientists mixed up the existing social groupings of nearly four dozen rhesus macaques at the Yerkes Research Center, observed behaviors among the new groups and analyzed blood samples to determine the cellular effects of the new social order. The team specifically measured effects on the peripheral immune system, which are immune cells that patrol other systems of the body, such as muscles.

Organizing the macaques into novel groups effectively created a new social hierarchy.  The first in the group became the most dominant and held the highest rank, while the last to join the group typically held the lowest status.

After each group’s hierarchy was established and behavior observed, the researchers took blood samples and treated the macaques with a synthetic stress hormone. The results showed the cells of the lower-status macaques were less able to respond productively to the hormone than those of the higher-status animals.

One explanation for this lack of a response was found within the macaques’ immune cells’ genetic information. Low-status females had immune cells that were less accessible to the signal from the hormone. In humans, stressful or traumatic situations have been linked to similar hormonal resistance.

“We know that social adversity early in life can have far-reaching effects that extend into adulthood,” Snyder-Mackler said. “The questions are, when do these events have to occur, how severe do they have to be and are they reversible or even preventable?”

Further research will help the researchers answer these questions, identify the magnitude of the effects of stress and, in the pursuit of improved human health, determine what might protect people from those impacts.

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