INDUCTION OF CYTOKINE GENE-EXPRESSION BY LISTERIOLYSIN-O AND ROLES OFMACROPHAGES AND NK CELLS

To determine the role of listeriolysin O (LLO) of Listeria monocytogen es in the host response at the initial stage of infection, cytokine ge ne expression in mouse peritoneal exudate macrophages and spleen cells was examined by reverse transcription-PCR. Expression of various cyto kine mRNAs, especially those of interleukin-1 (IL-1), tumor necrosis f actor 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 ge l electrophoresis. Induction of mRNA expression by LLO was as not bloc ked by cholesterol, which abrogated the hemolytic activity of LLO. Aft er the depletion of NK cells in spleen cells by treatment with anti-as ialo 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, i ncluding IL-1 alpha tumor necrosis factor alpha, and IL-12,was diminsh ed. In addition, IFN-gamma mRNA expression mas Impaired, indicating th at IFN-gamma mRNA expression from NK cells required signaling from mac rophages. It is suggested that LLO is capable of inducing endogenous c ytokines of mice, and both NK cells and macrophages are involved in th e host cytokine response to LLO.