Lm. Weiss et al., A CELL-CULTURE SYSTEM FOR STUDY OF THE DEVELOPMENT OF TOXOPLASMA-GONDII BRADYZOITES, The Journal of eukaryotic microbiology, 42(2), 1995, pp. 150-157
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.