Summary of Research Project Results under JSPS FY2001
"Research for the Future Program"

1.Research Institution Kyoto University
2.Research Area Life Sciences
3.Research Field Infectious Diseases and Bioregulation
4.Term of Project FY 1997 〜 FY 2001
5.Project Number 97L00706
6.Title of Project Basic Analysis of Bacterial Infection with Respect to Escape and Virulence Mechanism of Bacteria and its Application to the Host Defense

7.Project Leader
Name Institution,Department Title of Position
Masao, Mitsuyama Kyoto University, Gradudate School of Medicine Professor

8.Core Members

Names Institution,Department Title of Position
Ikuo, Kawamura Kyoto University, Graduate School of Medicine Assistant Professor
Mitsuaki, Nishibuchi Kyoto University, South-East Asian Research Center Professor

9.Summary of Research Results

Mycobacterium and Listeria are representative intracellular parasitic bacteria and they are capable of resist bactericidal mechanism of phagocytes. TH1-dependent protective immunity is induced in infected host and is indispensable for the host defense. The major purpose of this study was to elucidate how the virulence/escape factors of intracellular parasitic bacteria are involved in the host response in terms of cytokine response and the generation of protective immunity. In addition, experimental model of intracellular parasitic fungal infection was established and molecular mechanism of infection with virulent Vibrios were also examined. The major results obtained in this study are summarized as follows;
1) A novel function of listeriolysin O (LLO), the central escape/virulence factor of Listeria monocytogenes, was found. It was clarified that LLO is highly capable of inducing host cytokine response resulting in TH1-dependent protective immunity.
2) Cytokine inducing activity was dependent on the N-terminal domain of LLO molecule independent from the original pore-forming cytolytic activity that was dependent on C-terminal domain. A similar dual function was observed also in many other related family proteins including pnumolysin or seeligeriolysin O.
3) LLO induced first IL-12 and IL-18 in macrophages, then these cytokine induced IFN-γ production from NK cells. Both TLR2 and 4 appeared to be involved in the initial response by macrophages. The presence of novel cytoplasmic protein was implicated in the response resulting in NF-κB activation in macrophages.
4) IL-12 and IFN-γ responses were critical in TH1 response of the host against viable BCG and the lack of these response is related to the ineffectiveness of vaccination with killed BCG. Some proteinaceous factor is implicated in the cytokine response induced only by viable BCG.
5) TH1-dependent immune response was characterized in S. schenkii infection. Virulence expression was rather dependent on the inherent pathogenicity than host condition.

10.Key Words

(1)Intracellular bacteria、(2)Escape factor、(3)Listeria
(4)Listeriolysin O、(5)Thiol-activated cytolysin、(6)TH1 cells