STAGE CONVERSION OF TOXOPLASMA-GONDII IN MOUSE-BRAIN DURING INFECTIONAND IMMUNODEPRESSION

The kinetics and pattern of expression of bradyzoite-specific proteins were studied in mouse brain during infection with Toxoplasma gondii, Parasites found in the brain 6 days after ingestion of cysts were expr essing only tachyzoite-specific proteins (anti-SAG1 antibodies being u sed as a marker). Bradyzoite-specific protein (Pb36) expression was fi rst found after 9 days in vacuoles containing mixed parasites simultan eously expressing SAG1 and Pb36 or cysts containing parasites expressi ng only the bradyzoite marker. Reactivation of toxoplasmosis was studi ed in mouse brain using corticosteroids for immunosuppression. Parasit es expressing SAG1 were first found 6 days after the beginning of trea tment, but a very heterogeneous pattern was found throughout the study , We simultaneously found vacuoles containing parasites expressing onl y SAG1 or containing intermediate stages or cysts containing parasites expressing only bradyzoite proteins. A striking observation was the m ultiplication of cysts in foci, suggesting that the immune suppression triggered the release of parasites from preexisting cysts but that th e factors inducing bradyzoite development remained fully effective in driving parasites into this pathway.