Cohen, S., Kaplan, J. R., Cunnick, J. E. et al. 1992. Chronic social stress, affiliation, and cellular immune response in nonhuman primates. Psychological Science 3, 301-304.

Animals in the unstable [group-] 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 influence of chronic social stress.