Evaluation of the Physiological Responses to Lipopolysaccharide in Different Genetic Populations of Pigs

Purdue University 2002 Swine Research Report. The activation of the innate immune system in growing pigs via peripheral injection of lipopolysaccharide (LPS) induces a pronounced inflammatory response and alters metabolism. This makes the use of LPS injection a valuable model in the study of the mechanisms of the inflammatory response. The inflammatory response is believed to be mediated via the action of proinflammatory cytokines such as tumor necrosis factor a (TNF-a) which are released by antigen presentation cells upon encountering LPS. Indeed, several investigators have demonstrated that peripheral injection of LPS increases circulating concentrations of TNF-a (Leininger et al., 2000; Webel et al., 1997; Wright et al., 2000). Additionally, peripheral LPS challenge has been shown to decrease circulating concentrations of IGF-I in growing pigs (Wright et al., 2000). However, genetic population differences for immunological and somatotropic responses to peripheral LPS have not been investigated. It has been demonstrated that certain genetic populations of pigs are more sensitive to immunological stressors when reared in sub-optimal environments. Pigs of a high lean genotype experience reduced growth performance and increased mortality rates as compared to a lower lean genotype when reared in facilities managed under a conventional weaning, continuous flow system (Frank et al., 1997; 1998). Furthermore, the mechanisms responsible for this increased environmental sensitivity have not been delineated. Peripheral injection of LPS may serve as a model to evaluate mechanisms responsible for genetic differences in sensitivity to environmental stressors. Our objective was to determine whether there were differences in the immunological and somatotropic responses to LPS in growing pigs belonging to different genetic populations.