title: Detection of the initial site of Toxoplasma gondii reactivation in brain tissue.
abstract: Detection of the initial site of Toxoplasma gondii reactivation in brain tissue is difficult because the number of latent cysts is small and reactivation is a transient event. To detect the early stage of reactivation in mouse brain tissue, we constructed a cyst-forming strain of T. gondii in the tachyzoite stage, specifically expressing red fluorescence. The PLK strain of T. gondii was stably transfected with a red fluorescent protein gene, DsRed Express, under the control of a tachyzoite-specific SAG-1 promoter and the resulting parasite was designated as PLK/RED. Tachyzoites of PLK/RED growing in Vero cells showed red fluorescence. When C57BL/6J mice were i.p. infected with tachyzoites of PLK/RED, red fluorescent tachyzoites were detected in their brains at the fourth day p.i. However, red fluorescent tachyzoites were not detected in BALB/c mice latently infected with PLK/RED, although non-fluorescent cysts were detected in their brains. After treatment of latently infected mice with dexamethasone for 1 month, the mice showed neurological symptoms. In mice with symptoms, red fluorescent tachyzoites were again detected in their brains and in other organs. To detect the initial site of reactivation, BALB/c mice latently infected with the strain were treated with dexamethasone for 3 weeks, and brains were excised before any symptoms appeared. Excised brains were examined for red fluorescence-positive sites. By a histological study of red fluorescent-positive sites, we detected a cyst containing red fluorescent zoites, which still had a PAS stain-positive cyst wall. A few red fluorescent zoites breaking away from the cyst were also observed. The stage-specific expression of fluorescent protein facilitates detection of a rare transient event and makes it possible to detect the initial site of reactivation.
authors.affiliation: Department of Veterinary Parasitological Diseases, Gifu University, Yanagido 1-1, Gifu 501-1193, Japan. atakashi@gifu-u.ac.jp
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Takashima
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Suzuki
authors.forename: Xuenan
authors.initials: X
authors.lastname: Xuan
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Nishikawa
authors.forename: Akihiro
authors.initials: A
authors.lastname: Unno
authors.forename: Katsuya
authors.initials: K
authors.lastname: Kitoh
mesh_terms: D000818:Animals; D001921:Brain / Q000469:parasitology*; D003907:Dexamethasone / Q000494:pharmacology; D005260:Female; D049408:Luminescent Agents; D008164:Luminescent Proteins; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D014122:Toxoplasma / Q000187:drug effects / Q000302:isolation & purification / Q000472:pathogenicity / Q000502:physiology*; D014124:Toxoplasmosis, Animal / Q000469:parasitology*; D016781:Toxoplasmosis, Cerebral / Q000469:parasitology*; D014774:Virulence; D000097573:Red Fluorescent Protein
chemical_list: D003907:Dexamethasone; D049408:Luminescent Agents; D008164:Luminescent Proteins; D000097573:Red Fluorescent Protein