Enhancing effect of Salmonella enteritidis SPA on nonspecific resistance.

The peritoneal macrophages from mice treated with soluble protective antigen (SPA) or lipopolysaccharide (LPS) showed an increase in chemotactic activity, but muramyl dipeptide (MDP)-induced macrophages did not show any enhancing effect. Conversely, the chemotactic activity of mice peritoneal neutrophils was enhanced by SPA, LPS or MDP treatment. The superoxide anion (O2-)-generating activity of SPA-induced macrophages was higher than LPS or MDP. And even 30 days after SPA treatment, a significant increase of O2(-)-generating activity was evident as compared to the control. SPA-induced macrophages showed a higher degree of intracellular killing of Listeria monocytogenes, in vitro, as compared to macrophages obtained from normal mice. In the studies of in vivo protection, the number of bacteria in the liver after challenging with L. monocytogenes was smaller in SPA-treated mice than in untreated mice. Also, SPA-treated mice showed an increased resistance to L. monocytogenes infection.