Induction of TNF-alpha mRNA in murine macrophages by virulent and avirulent strains of Salmonella choleraesuis serovar typhimurium and serovar Choleraesuis.

TNF-alpha mRNA induction in murine macrophages by virulent and avirulent Salmonella strains was measured in vitro by RT-PCR method. Virulence plasmid-cured strains of S. choleraesuis serovar Typhimurium and serovar Choleraesuis, and rpoS-defective mutant of S. choleraesuis serovar Typhimurium induced significantly higher level of TNF-alpha mRNA than their parent (virulent) strains in macrophages of C3H/HeN mice. When macrophages of LPS-low responder (C3H/HeJ) mice were used, the difference of the induction level was not observed, indicating that LPS was involved in the enhanced level of TNF-alpha mRNA induction by avirulent Salmonella strains. LPSs from virulent and avirulent strains were analysed, but no difference was found for cytokine-inducing activity, and chemical properties. Those results suggested that avirulent Salmonella strains were damaged more easily, and released more LPS in macrophages to enhance TNF-alpha induction.