Induction of cytokine gene expression by listeriolysin O and roles of macrophages and NK cells

To determine the role of listeriolysin O (LLO) of Listeria monocytogenes in the host response at the initial stage of infection, cytokine gene expression in mouse peritoneal exudate macrophages and spleen cells was examined by reverse transcription-PCR. Expression of various cytokine mRNAs, especially those of interleukin-1 (IL-1), tumor necrosis factor alpha, gamma interferon (IFN-gamma), and IL-12, was observed to occur in spleen cells after direct stimulation with an LLO preparation purified to a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Induction of mRNA expression by LLO was as not blocked by cholesterol, which abrogated the hemolytic activity of LLO. After the depletion of NK cells in spleen cells by treatment with anti-asialo GM1 antibody plus complement, LLO-induced expression of IFN-gamma mRNA was decreased, indicating that NK cells were the main source of IFN-gamma. After depletion of macrophages by passing spleen cells over a Sephadex G-10 column, expression of macrophage-derived cytokines, including IL-1 alpha tumor necrosis factor alpha, and IL-12,was diminshed. In addition, IFN-gamma mRNA expression mas Impaired, indicating that IFN-gamma mRNA expression from NK cells required signaling from macrophages. It is suggested that LLO is capable of inducing endogenous cytokines of mice, and both NK cells and macrophages are involved in the host cytokine response to LLO.