title: Malaria parasite induces tryptophan-related immune suppression in mice.
abstract: Plasmodium spp. cause the worst parasitic diseases in humans and evade host immunity in complicated ways. Activated catabolism of tryptophan in dendritic cells is thought to suppress immunity, which is mediated by an inducible rate-limiting enzyme of tryptophan catabolism, indoleamine 2,3 dioxygenase (IDO), via both tryptophan depletion and production of toxic metabolites. In various infections, including malaria, IDO is known to be activated but its biological significance is unclear; therefore, we investigated whether malaria parasites induce IDO to suppress host immune responses. We found that enzymatic activity of IDO was elevated systematically in our mouse malaria model, and was abolished by in vivo IDO inhibition with 1-methyl tryptophan. Experimental infection with Plasmodium yoelii showed that IDO inhibition slightly suppressed parasite density in association with enhanced proliferation and IFN-gamma production by CD4+ T cells in response to malaria parasites. Our observations suggest that induction of IDO is one of the immune mechanisms of malaria parasites.
authors.affiliation: Kyushu University Graduate School of Medicine, Department of Parasitology, 3-1-1, Maidashi, Fukuoka, 812-0054, Japan. tetztani@parasite.med.kyushu-u.ac.jp
authors.forename: K
authors.initials: K
authors.lastname: Tetsutani
authors.forename: H
authors.initials: H
authors.lastname: To
authors.forename: M
authors.initials: M
authors.lastname: Torii
authors.forename: H
authors.initials: H
authors.lastname: Hisaeda
authors.forename: K
authors.initials: K
authors.lastname: Himeno
mesh_terms: D000818:Animals; D000962:Antimalarials / Q000494:pharmacology; D015496:CD4-Positive T-Lymphocytes / Q000187:drug effects / Q000502:physiology; D002738:Chloroquine / Q000494:pharmacology; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004912:Erythrocytes / Q000469:parasitology; D005260:Female; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism; D007371:Interferon-gamma / Q000097:blood; D007737:Kynurenine / Q000097:blood; D008288:Malaria / Q000276:immunology* / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D010967:Plasmodium yoelii / Q000187:drug effects / Q000276:immunology*; D013997:Time Factors; D014364:Tryptophan / Q000031:analogs & derivatives / Q000097:blood / Q000276:immunology* / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D000962:Antimalarials; D004791:Enzyme Inhibitors; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase; D007737:Kynurenine; C028129:tryptophan methyl ester; D007371:Interferon-gamma; D002738:Chloroquine; D014364:Tryptophan