The avirulence of the cultivated P F strain of T. cruzi: VI. introduced immunotolerance in mice by a veryhigh inoculum

Abstract

Immunosuppression bp immunotolerance was obtained in mice by inoculat ing Trypanosoma cruzi avirulent PF strain in high doses to mice. Direct and indirect laboratory tests loere used to demoiistrate the above statements.Since our first works on avirulence of the T. cruzi PF strain we were surprised to find some vaccinated animals with po sitive blood cultures and only rarely with positive parasitemias (11,13, 14) .Although we couldn't define precisely the real nature of the fact, by then, we had already concluded th a t the observed parasites should be the same inoculated as vaccine. These trypanosomes did not in fect young mice.Among the various circumstances in which the fact happened, one specially called our attention -the relationship between it and the number of parasites inoculated as vaccine.For this reason we decided to verify if the phenomenon could be reproduced and explained as due to immunological tole rance. MATERIAL AND METHODSNinety three albino mice weighing lOg each were divided in three groups -the first group with 34 animals, the second one with 35 and the third with 25.The first group was vaccinated, subcutaneously, with 107 living trypanosomes of the PF strain from a culture 19 days old in Warren medium.The second group was vaccinated with 101 1 parasites just the same and by the same route.The third group was held as control. Eight and fifteen days after vaccination a peripheral blood search was performed for trypanosomes in the vaccinated mice On the fifteenth day, from each vac cinated group, 10 animals were selected at random and bled to death. From the lirst "* U S P . F a c u ld a d e d e M e d ic in a . R ib e irã o P r ê to . S . P a u lo . B ra s ii.