A comparison of cell-mediated immune responses in rhesus macaques housed singly, in pairs, or in groups

A variety of psychosocial factors have been shown to influence immunologica l responses in laboratory primates. The present investigation examined the effects of social housing condition on cell-mediated immune responses, comp aring rhesus macaques (Macaca mulatta) in three housing conditions (single, pair, and group). Subjects included 12 adults of both sexes in each housin g condition (N=36). Multiple blood samples (0, 4, 8, and 12 months) were co llected for immunological analyses, including lymphocyte subsets, lymphocyt e proliferation to pathogens and nonspecific mitogens, natural killer cell activity, and cytokine production. CD4(+) to CD8(+) ratios differed signifi cantly across housing conditions and singly caged subjects had significantl y lower CD4(+)/CD8(+) after the 4-month timepoint than did socially housed (pair and group) subjects. CD4(+) to CD8(+) ratios were positively correlat ed within subjects, suggesting a trait-like aspect to this parameter. Lymph ocyte proliferation responses to all four gastrointestinal pathogens differ ed across housing conditions (at least at the 0.08 level), as did prolifera tion responses to StaphA, and the production of cytokines (IFN-gamma, IL-2, and IL-10). Proliferation responses of singly caged monkeys did not differ from socially housed monkeys and the highest levels of both IFN-gamma and IL-10 were produced by group housed subjects. The data demonstrate that soc ial housing condition affects immune responses. While not unidirectional, t hese effects generally suggest enhanced immune responses for socially house d animals. Since rhesus monkeys live socially in nature, and the immune res ponses of singly housed animals differed from those housed socially, there is considerable motivation and justification for suggesting that the use of singly housed rhesus macaques may complicate interpretations of normal imm unological responses. This may have important implications for the manageme nt, treatment, and selection of primate subjects for immunological studies. (C) 2000 Elsevier Science B.V. All rights reserved.