Abstract
By using reverse transcription-PCR, cytokine gene expression was examined in mice 24 h after infection with various strains of Listeria spp. differing in virulence as determined by in vivo growth and 50% lethal dose values. All the virulent strains of Listeria monocytogenes induced the expression of mRNAs specific for interleukin-1 alpha (IL-1 alpha), gamma interferon (IFN-gamma), and tumor necrosis factor alpha (TNF-alpha) in the spleen of mice, while an L. monocytogenes strain incapable of producing listeriolysin O and strains of Listeria innocua induced the expression of TNF-alpha mRNA only. The levels of expression of IL-1 alpha and IFN-gamma mRNAs were proportional to the levels of listeriolysin O produced by each strain. Those strains which induced the expression of IFN-gamma were capable of generating protective immunity in the infected host, suggesting that the virulence-related induction of some cytokine at the initial stage of infection plays a role in the induction of acquired cellular resistance to L. monocytogenes.