Ž . Applied Animal Behaviour Science 68 2000 67–84 www.elsevier.comrlocaterapplanim A comparison of cell-mediated immune responses in rhesus macaques housed singly, in pairs, or in groups Steven J. Schapiro ) , Pramod N. Nehete, Jaine E. Perlman, K. Jagannadha Sastry Department of Veterinary Sciences, The UniÕersity of Texas M. D. Anderson Cancer Center, Rt. 2, Box 151-B1, Bastrop, TX 78602, USA Accepted 5 January 2000 Abstract A variety of psychosocial factors have been shown to influence immunological responses in laboratory primates. The present investigation examined the effects of social housing condition on Ž . cell-mediated immune responses, comparing rhesus macaques Macaca mulatta in three housing Ž . conditions single, pair, and group . Subjects included 12 adults of both sexes in each housing Ž . Ž . condition N s36 . Multiple blood samples 0, 4, 8, and 12 months were collected for immunological analyses, including lymphocyte subsets, lymphocyte proliferation to pathogens and nonspecific mitogens, natural killer cell activity, and cytokine production. CD4 q to CD8 q ratios differed significantly across housing conditions and singly caged subjects had significantly lower q q Ž . CD4 rCD8 after the 4-month timepoint than did socially housed pair and group subjects. CD4 q to CD8 q ratios were positively correlated within subjects, suggesting a trait-like aspect to this parameter. Lymphocyte proliferation responses to all four gastrointestinal pathogens differed Ž . across housing conditions at least at the 0.08 level , as did proliferation responses to StaphA, and Ž . the production of cytokines IFN-g, 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-g and IL-10 were produced by group housed subjects. The data demonstrate that social housing condition affects immune responses. While not unidirectional, these effects generally suggest enhanced immune responses for socially housed animals. Since rhesus monkeys live socially in nature, and the immune responses of singly housed animals differed from those housed socially, ) Corresponding author. Tel.: q 1-512-321-3991; fax: q 1-512-332-5208. Ž . E-mail address: sschapir@mdanderson.org S.J. Schapiro . 0168-1591r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S0168-1591 00 00090-3