STUDIES ON CRYOPRESERVATION OF TOXOPLASMA-GONDII AND ITS ANTIGENICITYIN MICE

Two strains (RH and GC, the latter of which is a Taiwan isolate of por cine origin) of Toxoplasma gondii were kept at -20 degrees C, -60 degr ees C, and in liquid nitrogen (-196 degrees C) to follow the time cour se change in viability and virulence of the parasites by direct count and animal inoculation methods. Changes in antibody titers in some of the mice inoculated with the thawed organisms were assayed by the indi rect immunofluorescent antibody test. Viability and virulence of T. go ndii were best preserved by storage in liquid nitrogen. Tachyzoites ke pt in liquid nitrogen for eight years still can lead to the death of t he injected mice in 2-3 weeks. Virulence of the tachyzoites could be m aintained for eight weeks at most at -20 degrees C and -60 degrees C. Dimethylsulfoxide (DMSO) seemed to be a better cryoprotectant for T. g ondii than glycerol, but the DMSO-preserved organisms resulted in fewe r tachyzoite-containing peritoneal exudates in inoculated mice than th e glycerol-preserved organisms. The local isolate (GC strain) tachyzoi tes tolerated cryopreservation less well than the RH strain parasites. Low antibody titers (at most 1:64) were produced in mice that survive d more than 16 days after inoculation with thawed tachyzoites.