Tehran University of Medical Sciences Iranian Journal of Parasitology 1735-7020 11 1 2016 03 14 81 85 Mahboobeh SALIMI Department of Medical Parasitology and Mycology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran Saeedeh SHOJAEE Department of Medical Parasitology and Mycology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran Hossein KESHAVARZ Department of Medical Parasitology and Mycology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran AND Center for Research of Endemic Parasites of Iran (CREPI), Tehran University of Medical Sciences, Tehran, Iran Mehdi MOHEBALI Department of Medical Parasitology and Mycology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran AND Center for Research of Endemic Parasites of Iran (CREPI), Tehran University of Medical Sciences, Tehran, Iran 2016 03 14 2016 03 14 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. https://ijpa.tums.ac.ir/index.php/ijpa/article/view/813 https://ijpa.tums.ac.ir/index.php/ijpa/article/download/813/656