• Parasites, Hosts and Diseases
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• v.36 no.3
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• pp.191-198
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• 1998

The responses to antifolales of ToxopLasmc Bondii were investigated by measuring the dihydrorolate redLlctase (DHFR) activity. quantity of DHFR mRNA, and single-strand conformational polymorphism (SSCP) pattern. Pyrimethamine (PYM) and methotrexate (MTX) were tested ds anlifolates. When T. gondii was treated wish PYM, the viability was decreased by the increasing concentration of PYM. DHFR activity tended to increase as the passage proceeded. and the quantity of mRNA expressed was also increased according to passages. The viability of 7. gonnii was decreased by the increasing concentration of MTX, but it was maintained over 40% up to $100{\;}{\mu\textrm{m}}$ MTX. DHFR activity was 77.4% in the 1st passage ($1{\;}{\mu\textrm{m}}$). 82.2% in the 4th passage ($10{\;}{\mu\textrm{m}}$), and 141.3% in the 7th passage ($100{\;}{\mu\textrm{m}}$) But no changes were detected in SSCP pattern of T gondii rxposvd to FYM and MTX. both. These results suggested that the response of T gondii to FYN was rofulalcd by transrriptional level and that, in MTX. the viability of T. gonnii was derived from increasing DHFK activity.