Social stress in laboratory rats: behavior, immune function, and tumor metastasis.

This report summarizes data from social confrontations studies in laboratory rats dealing with the effects of psychosocial stress on immune functioning and tumor metastasis. The paper focuses on the physiological alterations observed in subdominant males after 2 days of continuous social confrontation. A significant loss of body mass and elevated plasma concentrations of adrenal hormones in subdominant males indicate a stressful social environment. Subdominant males showed lower numbers of blood CD4 and CD8 T cells as well as reduced activity levels of T cells and natural killer (NK) cells relative to control subjects. In order to evaluate the possible health impact of suppressed NK functioning, we used the MADB 106 tumor model. A 10-fold lower tumor clearance in subdominant males demonstrates suppression of the animals' capacity to prevent metastatic development. The relationship between individual behavior and immunological outcome is briefly discussed. Together, the study of male rats in social confrontations appears to be a good model to investigate stress-induced immune modulation and tumor metastasis under relatively naturalistic social conditions.