Social stress may affect people not just emotionally but also at the genetic level, a recent Duke study suggests.
Jenny Tung, visiting assistant professor of evolutionary anthropology, studied 49 female rhesus macaques to investigate the effect of social ranking on health. She found a link between social rank and immune system gene expression such that she could predict social status based on gene expression data with 80 percent accuracy.
These findings, published this month in the journal Proceedings of the National Academy of Sciences, may be useful in analyzing the effects social stress has on the human immune system, Tung noted.
Low-ranking macaques had higher levels of stress, resulting in greater gene expression in genes associated with the immune system. The greater gene expression—the transfer of information from an organism’s genes to its physical appearance—resulted in higher levels of inflammation in the immune system, which can make low-ranking macaques more susceptible to becoming sick.
“We found that genes that tended to be turned up higher in low-ranking individuals were related to the immune system about twice as often as one would expect just by chance,” Tung said. “This dovetails with some evidence that people have been recording for some time that social stress tends to be associated with high rates of inflammation.”
These low-ranked macaques can face long-term harassment, Tung said. Other macaques may steal their food or make faces at them. The stability of the social hierarchies means this harassment causes chronic stress, which led to the elevated levels of immune system gene expression.
The study was developed for female macaques only because their social ranking depends on when they are introduced to a new environment, whereas males’ social ranking is determined by competition, Tung said. It is easier to manipulate the social status of female macaques because their introduction to a new environment can be controlled.
Anne Pusey, chair and James B. Duke professor of evolutionary anthropology, noted that a controlled study on the effects of social status on human health is not possible.
“Tung’s monkey studies provide very promising model systems for continued investigation of the physiological mechanisms involved [in humans] and how they may be altered,” Pusey wrote in an email Sunday.
The process by which social standing influences primate physiology is still not well understood, Tung noted.
“If social environment influences risk of disease or even mortality rates, well, there is a bit of a black box between social exposure and its effect on our physiology,” she said. “Some people have posed this question as how the social environment gets under the skin. A lot of progress has been made in that vein over the past couple of decades, but we still don’t have a complete answer.”
Susan Alberts, professor of biology, said although a controlled study on how social interconnectedness affects the human immune system is not possible, Tung’s study is still applicable to humans.
“We are primates, and it’s almost impossible to imagine that if we find broad general principles that affect gene expression and physiology in one primate, there isn’t going to be something useful about that information when thinking about another species,” Alberts said. “So does [the study] provide us with an understanding of the evolutionary roots of these kinds of relationships? Yes.”
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