Effects of dominance status and environmental enrichment on cell-mediated immunity in rhesus macaques

Psychosocial variables have been shown to affect cell-mediated immune responses in captive macaques. To explore whether one major (social dominance) and/or one minor (environmental enrichment) psychosocial variable affected immune responses in female rhesus monkeys, cell-mediated immune responses were compared in six monkeys that were the highest ranking and 12 monkeys that were middle ranking in their respective social groups. All subjects were 5- and 6-year-old rhesus living in stable unimale-multifemale groups, and were matched on social history, parity, weight, and health characteristics. Highest-ranking females had significantly lower mitogen-induced proliferation responses to lipopolysaccharide and pokeweed mitogen and higher natural killer cell activity, CD4⁺ lymphocyte counts, and CD8⁺ lymphocyte counts than did middle-ranking females. These data demonstrate that dominance rank, an important psychosocial factor, affects immune response in a stable social setting. One-half of the subjects (three highest-ranking and six middle-ranking) received a variety of environmental enhancements between the ages of 1 and 4 years (the enriched group), while the other nine subjects did not (the control group). No differences between enriched and control groups reached statistical significance, but some interesting trends appeared, tentatively suggesting that a minor psychosocial manipulation, inanimate enrichment, may subtly affect cell-mediated immune responses. The relationship between psychosocial factors and cellular immune function may have important implications for disease progression and for the management, treatment, and selection of primate subjects for studies in which immunological variables are of interest.