Reduced serum antibodies associated with social defeat in rats.

Many studies have linked various physical stressors with changes in immune function. The present experiment examined the effect of a social stressor, defeat associated with territorial defense, on serum antibodies to a specific protein, keyhole limpet hemocyanin (KLH). Pairs of male rats formed colonies and experimental rats were intruders. Experimental animals were immunized with KLH prior to exposures to territorially defensive colonies. Control animals were placed into colonies but separated from residents by a Plexiglas barrier. Behavioral measures, including number of bites and total time spent in submissive postures, were taken for colony-intruder interactions. Serum antibody levels were determined from blood samples taken one, two, and three weeks following immunization. Experimental animals had significantly less serum antibodies to KLH than did controls. Within the experimental group, total time spent in submissive postures at week one was significantly correlated with serum antibody levels, such that animals spending the most time in submission had lower antibody levels. Total bites correlated only slightly with antibody levels. The correlation between submission and serum antibody levels increased when the bites factor was partialled out. A stressful social encounter may thus affect immune function in a manner independent of the influence of physical (nociceptive) stressors.