Immunity changes in confined animals: a route to disease?

An intriguing and important biological question is how the immune system is subject to regulation by exogenous factors. In the mouse system, our laboratory has demonstrated that a wide variety of environmental stimuli, such as heat, cold, short-term restraint and conditioned-taste aversions, affect cell-mediated immune events in vivo. The reduction in cell-mediated immunity that is caused by restraint can be abolished by adrenalectomy or treatment with an inhibitor of corticosterone biosynthesis. We have therefore examined the effect of a short-term restraint stressor on the immune system of pigs. Five-to-eight-week-old-pigs were restrained by placing them in an expanded-metal box for 2 h each day for 3 consecutive days. Restraint caused a significant increase in serum cortisol. Preliminary evidence indicates that restraint significantly reduced size of the thymus gland from 0.14% to 0.10% of body weight and also significantly reduced in vivo phytohemagglutinin-stimulated, cell-mediated reactions by 25%. Addition of cortisol at a concentration of 130 ng/ml to phytohemagglutinin and concanavalin A-stimulated porcine lymphocytes in vitro reduced mitogenesis of splenocytes, peripheral blood lymphocytes and thymocytes. Although these data reflect changes in immune function caused by an acute environmental stressor in vivo and by cortisol in vitro, research from another laboratory indicates that longer-term restriction of pigs with tethers and farrowing crates can also decrease immune events.(ABSTRACT TRUNCATED AT 250 WORDS)