title: Cytolysin-dependent escape of the bacterium from the phagosome is required but not sufficient for induction of the Th1 immune response against Listeria monocytogenes infection: distinct role of Listeriolysin O determined by cytolysin gene replacement.
abstract: Listeria monocytogenes evades the antimicrobial mechanisms of macrophages by escaping from the phagosome into the cytosolic space via a unique cytolysin that targets the phagosomal membrane, listeriolysin O (LLO), encoded by hly. Gamma interferon (IFN-gamma), which is known to play a pivotal role in the induction of Th1-dependent protective immunity in mice, appears to be produced, depending on the bacterial virulence factor. To determine whether the LLO molecule (the major virulence factor of L. monocytogenes) is indispensable or the escape of bacteria from the phagosome is sufficient to induce IFN-gamma production, we first constructed an hly-deleted mutant of L. monocytogenes and then established isogenic L. monocytogenes mutants expressing LLO or ivanolysin O (ILO), encoded by ilo from Listeria ivanovii. LLO-expressing L. monocytogenes was highly capable of inducing IFN-gamma production and Listeria-specific protective immunity, while the hly-deleted mutant was not. In contrast, the level of IFN-gamma induced by ILO-expressing L. monocytogenes was significantly lower both in vitro and in vivo, despite the ability of this strain to escape the phagosome and the intracellular multiplication at a level equivalent to that of LLO-expressing L. monocytogenes. Only a negligible level of protective immunity was induced in mice against challenge with LLO- and ILO-expressing L. monocytogenes. These results clearly show that escape of the bacterium from the phagosome is a prerequisite but is not sufficient for the IFN-gamma-dependent Th1 response against L. monocytogenes, and some distinct molecular nature of LLO is indispensable for the final induction of IFN-gamma that is essentially required to generate a Th1-dependent immune response.
authors.affiliation: Department of Microbiology, Kyoto University Graduate School of Medicine, Yoshida-konoecho, Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Hideki
authors.initials: H
authors.lastname: Hara
authors.forename: Ikuo
authors.initials: I
authors.lastname: Kawamura
authors.forename: Takamasa
authors.initials: T
authors.lastname: Nomura
authors.forename: Takanari
authors.initials: T
authors.lastname: Tominaga
authors.forename: Kohsuke
authors.initials: K
authors.lastname: Tsuchiya
authors.forename: Masao
authors.initials: M
authors.lastname: Mitsuyama
mesh_terms: D000818:Animals; D001427:Bacterial Toxins / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology; D002478:Cells, Cultured; D015169:Colony Count, Microbial; D003593:Cytoplasm / Q000382:microbiology; D004195:Disease Models, Animal; D005260:Female; D017353:Gene Deletion; D006360:Heat-Shock Proteins / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology / Q000502:physiology*; D006460:Hemolysin Proteins / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology / Q000502:physiology*; D007371:Interferon-gamma / Q000096:biosynthesis; D008089:Listeria monocytogenes / Q000235:genetics / Q000276:immunology*; D008088:Listeriosis / Q000276:immunology* / Q000517:prevention & control; D008264:Macrophages / Q000382:microbiology; D051379:Mice; D008809:Mice, Inbred C3H; D010588:Phagosomes / Q000382:microbiology; D013154:Spleen / Q000382:microbiology; D016019:Survival Analysis; D016176:T-Lymphocyte Subsets / Q000276:immunology; D018417:Th1 Cells / Q000276:immunology*
chemical_list: D001427:Bacterial Toxins; D006360:Heat-Shock Proteins; D006460:Hemolysin Proteins; D007371:Interferon-gamma; C038705:hlyA protein, Listeria monocytogenes