DIFFERENCE IN SUSCEPTIBILITY TO LYSIS BETWEEN CLONES OF THE Y-STRAIN OF TRYPANOSOMA-CRUZI

Three clones isolated from the Y strain of Trypanosoma cruzi - YP1, YP 2 and YP3 - were adapted to in vitro cultivation in VERO cells. The re covery of the parasites from the Y strain and clone YP3 was similar af ter 24 hr of contact with cells (3.2% and 2.7%, respectively) and much lower than the recovery of clones YP1 and YP2 (56.7% and 60.0% of ino culum, respectively). After five days incubation, the ratio Trypomasti gotes/Amastigotes released into the supernatants was about 90/10 for c lone YP1, YP3 and Y strain, and 50/50 for clone YP2. After nine days, the ratio was 62138 for clone YP1, 97/3 for clone YP3, 81/19 for Y str ain and 50/50 for clone YP2. The susceptibility of tissue culture deri ved trypomastigotes (TCT) to lysis in the presence of chronic chagasic human sera and human complement was assessed using Complement Mediate d Lysis reaction (CML). Trypomastigotes from clone YP2 were consistent ly less susceptible to CML (% lysis less than 20), than parasites from the other clones and Y strain. Parasites of clone YP3 had susceptibil ity to CML comparable to that of the Y strain (about 70%), while TCT o f clone YP1 had intermediary susceptibility (40%).