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. conclusion: alkalization of culture medium to ph 8 induced expression of bradyzoite- specific proteins and production of rh cysts in cell culture.