Personality modulates proportions of CD4 + regulatory and effector T cells in response to socially induced stress in a rodent of wild origin.

The way how individuals respond to chronic challenges can vary tremendously, and such differences are closely linked to personality. The few available studies on individual differences in stress-related immunosuppression in non-human mammals have been mainly carried out with laboratory strains. We conducted a study in male mound-building mice (Mus spicilegus) of wild origin. We distinguished between high (HAN) and low anxious/neophobic (LAN) personality types, quantified by subjects' consistent and associated behavioral responses in repeated elevated plus maze and novel object tests. After reaching maturity, parts of the subjects were regularly confronted to different resident pairs over a period of 5days to provoke a condition of chronic social stress, while others were used as untreated controls. We measured fecal corticosteroid metabolite (FCM) concentrations and different cellular immune parameters from blood and spleen. Socially confronted HAN showed higher increases in FCM concentrations than LAN, indicating a more pronounced physiological stress response in the former personality type. HAN of the experimental group also showed lower percentages of effector T cells (Teff) and higher regulatory T cells (Treg) in the spleen; the latter are known for their immunosuppressive activity. Considering the ratio of Teff/Treg, animals with higher increases in FCM concentrations during the late period of the experiment showed a stronger shift towards Treg cells, supporting immunosuppressive effects of chronically elevated corticosteroid levels. Summarizing, our results strongly suggest that immunomodulatory effects of socially induced stress were altered by individual differences in anxiety/neophobia, emphasizing the significance of personality in shaping physiological responses to challenge.