Social status can be used as predictor of life expectancy and overall health. It is easy to conclude that this is a result of better diet, healthcare, and lack of external risk factors but, as a team of researchers reported in the November 25th issue of the journal Science, movement in social status in rhesus macaques influenced changes in immune system phenotypes.
The study experimentally manipulated the social status of 45 adult female rhesus macaques by sequential introduction of the macaques into newly constructed social groups. An earlier introduction to a group predicts a higher social standing. At the midpoint of the study the primates were rearranged in the same or adjacent groups by performing another round of sequential introduction. In both phases of the study, the order of introduction to a group accurately predicted social status which in turn influenced rates of harassment and grooming behavior of the macaques.
The arrangement of the social status among the groups revealed differences in the primate’s leukocyte composition. RNA sequencing on 5 major types of immune cells identified Natural Killer cells and Helper T cells as the most sensitive to social ranking. After rearrangement of the groups and alterations of the dominance hierarchy, the gene expression profiles of the NK and T helper cells altered and correlated with the new social status.
The researchers also monitored the immune response of the primates using TruCulture®, an ex vivo whole-blood collection and leukocyte culture system. Both a control and a lipopolysaccharide-stimulated sample were taken in parallel for each macaque and examined using RNA sequencing. Pro-inflammatory genes were activated in cells from the primates with a subordinate social status where as higher ranking monkeys activated anti-viral genes.
These experiments together demonstrate how social hierarchy alone can alter a primate’s immune system and response to external stimuli. The study also suggests that although social status can affect one’s health, the damage may be reversible. The immune system altered in the macaques as they moved up and down the social ladder. An inflammatory response in an infected individual is an integral part of the immune system but unnecessary inflammation can damage organs. This evidence suggests why people with lower social status have increased risk in developing inflammatory diseases and a lower life expectancy.