In vitro cultivation of Toxoplasma gondii cysts in astrocytes in the presence of gamma interferon.

Long-term culturing of Toxoplasma gondii cysts was accomplished in vitro in association with murine astrocytes and intermittent additions of gamma interferon to the media. Phase-contrast microscopy was used to follow the stages of cyst development, and electron microscopy confirmed the presence of morphologic characteristics of T. gondii cysts. T. gondii cysts formed in vitro had a single trilaminar membrane during both intracellular and extracellular existence and contained amorphous electron-dense material either throughout the cyst or in a uniform layer under the trilaminar membrane. The bradyzoites were similar to previous descriptions of tachyzoites in vitro except that they were smaller and contained numerous electron-lucent vacuoles. Gamma interferon is not necessary for cyst formation, but it controls the division of tachyzoites and may allow cysts to remain for prolonged periods without rupturing. In vitro-cultivated T. gondii cysts will be useful for producing bradyzoite and cyst antigens and for measuring the effects of antimicrobial agents and immune modulators on the viability of intracystic T. gondii.