Effects of social manipulations and environmental enrichment on behavior and cell-mediated immune responses in rhesus macaques

This paper reviews a series of studies that have examined the effects of manipulations to the social and the inanimate environments on the behavior and cell-mediated immune responses of rhesus macaques of various ages living in different settings. In general, enrichment of the inanimate environment with toys, structures, foraging devices, and/or videotapes increased the amount of species-typical behavior expressed by the monkeys, but did not affect their immune responses. Housing monkeys socially, on the other hand, not only resulted in increased time spent in species-typical activities, but also resulted in (1) decreases in time spent in abnormal behavior and (2) changes in a number of immune parameters. Additionally, attempts to directly influence the affiliative interactions of socially housed adult rhesus have resulted in systematic changes in affiliative behavior, although anticipated accompanying systematic alterations to cell-mediated immune responses have yet to be realized. The data suggest that aspects of the physical and social environments influence behavioral and immunological parameters in captive macaques in the absence of other experimental manipulations. As such, these influences need to be appropriately managed and/or controlled in order to minimize potential confounds in experimental designs.