Cyst Formation from Virulent RH Strain of Toxoplasma gondii Tachyzoite: In Vitro Cultivation.
BACKGROUND
This study was performed to induce conversion of RH strain tachyzoites of Toxoplasma gondii to bradyzoites by pH changing of the culture medium.


METHODS
HeLa cell monolayers were infected at a 1:1 tachyzoite to cell ratio. Four hours after infection, the culture medium was removed and replaced with culture medium and 5% FCS, adjusted to pH 8 with NaOH. The culture was maintained at 37 °C without CO2 until the end of the experiment. Cyst-like structures were collected and stained with periodic acid schiff (PAS) staining method. The soluble antigens of cyst-like structures of RH strain, in addition to RH tachyzoite, bradyzoites of avirulent Tehran strain and uninfected HeLa cells were electrophoresed on 12.5% polyacrylamide gel. The gel was stained by coomassie brilliant blue R-250.


RESULTS
Four days after infection of HeLa cells with tachyzoites of T. gondii, RH strain, cyst- like structures were noticed and stained with PAS. In the SDS-PAGE, protein bands of these structures had some differences with tachyzoites of RH strain, but there was quite similarity between protein bands of these structures and tissue cysts (bradyzoites) of Tehran strains. P34 and P36 (bradyzoite-specific proteins) were observed only in T. gondii bradyzoites of RH (cyst like structures) and bradyzoites of Tehran strains.


CONCLUSIONS
Alkalization of culture medium to pH 8 induced expression of bradyzoite- specific proteins and production of RH cysts in cell culture.
Department of Medical Parasitology and Mycology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran.
Mahboobeh
M
Salimi
Department of Medical Parasitology and Mycology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran.
Saeedeh
S
Shojaee
Department of Medical Parasitology and Mycology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran; Center for Research of Endemic Parasites of Iran (CREPI), Tehran University of Medical Sciences, Tehran, Iran.
Hossein
H
Keshavarz
Department of Medical Parasitology and Mycology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran; Center for Research of Endemic Parasites of Iran (CREPI), Tehran University of Medical Sciences, Tehran, Iran.
Mehdi
M
Mohebali
Cell culture; Cyst; RH strain; Toxoplasma gondii