A CELL-CULTURE SYSTEM FOR STUDY OF THE DEVELOPMENT OF TOXOPLASMA-GONDII BRADYZOITES

Toxoplasma gondii is a ubiquitous apicomplexan parasite and a major op portunistic pathogen under AIDS-induced conditions, where it causes en cephalitis when the bradyzoite (cyst) stage is reactivated. A bradyzoi te-specific Mab, 74.1.8, reacting with a 28 kDa antigen, was used to s tudy bradyzoite development in vitro by immune-electron microscopy and immunofluorescence in human fibroblasts infected with ME49 strain T. gondii. Bradyzoites were detected in tissue culture within 3 days of i nfection. Free heating cyst-like structures were also identified. West ern blotting demonstrated the expression of bradyzoite antigens in the se free-floating cysts as well as in the monolayer. Bradyzoite develop ment was increased by using media adjusted to pH 6.8 or 8.2. The addit ion of gamma-interferon at day 3 of culture while decreasing the total number of cysts formed prevented tachyzoite overgrowth and enabled st udy of in vitro bradyzoites for up to 25 days. The addition of IL-6 in creased the number of cysts released into the medium and increased the number of cysts formed at pH 7.2. Confirmation of bradyzoite developm ent in vitro was provided by electron microscopy. It is possible that the induction of an acute phase response in the host cell may be impor tant for bradyzoite differentiation. This system should allow further studies on the effect of various agents on the development of bradyzoi tes.