Via BBC News: Social rank 'linked to immunity'. Excerpt:
A study of rhesus macaque monkeys may have solved a long-standing puzzle on a link between social rank and health.
A study of 10 social groups of macaque females showed that the activity level of an individual's immune genes was an accurate predictor of her social rank.
In a paper in Proceedings of the National Academy of Sciences, the team also showed that the monkey's immunity changed when social rank was altered.
The work suggests that status drives immune health, rather than vice-versa.
A great many studies have shown associations in both humans and non-human primates between social environment and biological markers of health.
In previous studies of rhesus macaques, the so-called dominance rank has been correlated to levels of the stress-linked glucocorticoid hormones, sex hormones, the brain chemicals serotonin and dopamine, and white blood cell counts.
But one unanswered question concerns cause and effect: does a compromised immunity or imbalance of some chemical cause a particular social rank, or does taking on a particular social rank set the immune system and neural dials?
Jenny Tung, now at Duke University, and colleagues addressed this question by carefully assigning social rank to 10 groups of rhesus macaques, each containing five females.
This can be done by altering the order in which females are introduced into the group; the later she arrives, the lower her social rank.
The team then measured the levels of a broad class of immune cells, peripheral blood mononuclear cells, in the bloodstream.
They found that on the basis of those levels of circulating immune cells alone, they could predict an individual female's social rank with 80% accuracy.