Response to removal from and return to a social group in adult male rhesus monkeys.

The removal of four adult rhesus monkeys from a large social group (n = 85) to peer housing resulted in no significant changes in basal cortisol levels or absolute numbers of T lymphocyte subsets 24 h later. However, the return of these males 1 year later to the same social group resulted in significant increases in cortisol levels (66 +/- 21%) and significant decreases in T-helper (-31.6 +/- 15.8%) and T-suppressor cells (-35.2 +/- 8.7%) 24 h later. Blood samples for immune and cortisol measurements were obtained before and 24 h following both the removal and the return 1 year later. Aggressive and sexual behavioral data were recorded on audiotape for 3.5 h following the reintroduction using an all occurrences of some behaviors sampling technique. Analyses revealed a negative correlation between percent change from baseline in T-helper cells 24 h following the return and the frequency of bites (nonwounding) and chases received during the 3.5 h following the return. The absence of a stress response to separation in adult males is in contrast to the presence of a stress response observed in infants, juveniles, and adult females and possibly is due to sex differences in group attachment in sexually mature males. On the other hand, the return to the social group did induce a psychosocial stress response in the males, and the degrees of the stress, as determined by cortisol and immune cell measures, was related to the agonistic interactions experienced by the individuals.