CHRONIC SOCIAL STRESS, AFFILIATION, AND CELLULAR IMMUNE-RESPONSE IN NONHUMAN-PRIMATES

We report the first experimental study of the effect of long-term (over 2 years) exposure to a stressor on cellular immune response. Forty-three male cynomolgus monkeys were randomly assigned to stable or unstable social conditions for 26 months. The proportion of time spent in affiliative behaviors was assessed by observations made twice weekly. T-cell immune response (mitogen-stimulated cell proliferation) was assessed weekly for 3 weeks immediately following the 26-month manipulation. The possibility that affiliative behavior represents an attempt to cope with social stress was supported by greater affiliation among animals in the unstable condition than in the stable condition. Animals in the unstable condition also demonstrated relatively suppressed immune response. More affiliative animals showed enhanced immune response, with the beneficial effects of affiliation occurring primarily among unstable animals. The data are interpreted as consistent with the stress-buffering hypothesis; that is, affiliation protects animals from the potentially pathogenic influences of chronic social stress.