Alteration of Neutrophil Function in BCG-Treated and Non-Treated Swine after Exposure to Salmonella typhimurium

Abstract

<p><em>Salmonella typhimurium</em> infection in swine causes an enterocolitis followed by a persistent carrier state, but little is known about the mechanisms that allow this organism to colonize and persist in host tissues. Neutrophils provide a first line of defense against invading pathogens such as <em>Salmonella typhimurium</em>. The purpose of this study was to evaluate porcine neutrophil function after in vivo exposure to <em>Salmonella</em> and to determine if the immunomodulator, bacillus Calmette Guerin (BCG), exerts any effect on neutrophil function or on the colonization and persistence of <em>S. typhimurium</em> in the pig. Compared to negative controls, neutrophils from pigs exposed to <em>S. typhimurium</em> exhibited significantly decreased iodination, cytochrome-C reduction, antibody-dependent cell-mediated cytotoxicity, random migration, and chemotaxis (<em>P</em>≤0.05). Neutrophil bactericidal activity against <em>S. typhimurium</em> was significantly enhanced. Most of the significant differences were noted in the first two days after exposure to <em>Salmonella</em>. Often the functional alterations were biphasic, peaking again 7–10 days after exposure. BCG alone significantly depressed random migration and cytochrome-C reduction in unstimulated neutrophils. The clinical course, colonization pattern, and persistence of <em>Salmonella</em> were similar between pigs receiving BCG and untreated pigs. These data suggest that <em>S. typhimurium</em> infection causes a depression in oxidative metabolism and motility, yet an increase in overall bactericidal activity against <em>S. typhimurium</em> in circulating porcine neutrophils. It also appears that BCG treatment, as reported here, does not enhance resistance of pigs to <em>S. typhimurium</em> colonization or reduce the number of persistent organisms in the porcine ileum.</p>