Research over the past few years has linked man's physical or social environment to their well-being. Stress suppresses the body and compromises the immune system, leaving a person more vulnerable to diseases and other conditions. Different stressors, from family anxiety to air pollution, can lead to inflammation, diabetes and heart disease.
But scientists do not fully understand how the relationship between stress and health develops on a cellular level. A new study, led by the University of Washington, examines one key stressed condition – the consequences of the social hierarchy – and how cells respond to the hormones released in response to this stress. They found that social status determines how individual macaques meet a key hormone of stress – glucocorticoid.
"The goal is to understand the mechanisms by which social experiences or the environment" fall under the skin, "so to say, affect health and survival," says lead author Noah Snyder-Mackler, UW's Psychology Assistant.
The study was published on December 11, Collection of the National Academy of Sciences,
For this study, Sneijder-McLuhr and the team turned to a non-human social primate: the sharp macaque. Scientists mix existing social groups of nearly four dozen macaques, observe behavior among new groups and analyze blood samples to determine the cellular effects of the new social order. The team specifically measures the effects on the peripheral immune system, which are immune cells that patrol other body systems such as muscles.
Mackerels are an appropriate subject of this study, Snyder-McLuer explained, because they are relatively close cousins of humans but do not have specific cultural or societal factors such as substance use or access to medical care that can complicate any relevant human health research.
The new study covers Snyder-Mackler's post-graduate studies at Duke University, which in a study in 2016 suggests that social status has a direct effect on the immune system. This study changes groups of monkeys to see how cells react to what will happen in a short-term stress situation.
In humans and other primates, social status is related to health and quality of life. Lower social status may mean less social and community support and fewer buffers against stress or unfavorable circumstances. In the case of animals, this amounts to fewer allies and more harassment by peers, whereas for people, the lower status is often related to income struggle, employment and the stability of the relationship.
Organizing the macaques in nine new groups has actually created a new social hierarchy, the authors wrote, according to which the order in which each monkey was introduced, also defines its status. The first in the group became the most dominant and occupies the highest rank, while the latter joins the group, usually has the lowest status.
Once the hierarchy of each group has been established and the team can monitor the behavior of the macaques, the researchers have taken blood samples and treated them with a synthetic glucocorticoid – which mimics the natural major stress hormone of the macaques. In both macaques and humans, glucocorticoid hormones are activated to mobilize resources during increased stress; ways in which cells respond to the stress hormone leap may show whether the body can react appropriately to the stressor or whether the pathway that damages the body and makes it more susceptible to illness is chronically activated.
By using synthetically processed blood samples to simulate what is happening inside macaques during acute stress, researchers could show how glucocorticoid hormone can affect cellular behavior in different macaques – especially whether macaques respond productively to the stress hormone or are worn out from it and no longer responds appropriately. In this experiment, cells of lower-grade macaques are less able than those of higher-order animals to respond productively to glucocorticoid. One explanation for this lack of response was found in the genetic information on the macaque immune cells. By measuring the availability of the chromatin – how the DNA is packed in the cell – they find that women with low status have immune cells that are less accessible to the glucocorticoid signal.
In people, stressful or traumatic situations such as loss of work, caring for a chronically ill child, or grief of a close person are related to the resistance of glucocorticoids – the physical stress on the cellular level of stress on the human body. Sneijder-McLuer's work implies a possible mechanism, namely modified access to chromatin, which may be based on the resistance of glucocorticoids to low-status individuals.
"Given shared biology and the evolutionary history between monkeys and humans, these discoveries help us better understand how social status can affect people," said Snyder-McLuhr.
Further research is needed to determine the magnitude of the effects of stress caused by the change in social status and what buffers can protect individuals from these impacts. Not all people react similarly to the same stress; some of them are more resilient or susceptible to the same stressful stress.
"We know that social injustices at the beginning of life can have profound consequences that extend to adulthood. The question is when should these events happen, how severe they are, whether they are reversible or can even be prevented? "Snaider-McLuer said.