THE AVIRULENCE OF THE CULTIVATED Y STRAIN OF TRYPANO- SOMA CRUZI IV — THE EFFECT OF IMMUNOSUPPRESSIVE AGENTS IN MICE.

Antiprolifer ative drugs (Azathioprine and Methotrexate) were able to enhanoe a T. cruzi virulent infectkm in mioe, but failed to induce evident in-fectibn in animais previously vaccinateã with the live PF strain of the same parasite. Vinblastine (Vbl) had a similar effect w ith the virulent Y strain, but pro-moted the appearance of positive blood eultures in animais vaecinated and treated previously w ith the drug. Negative results are obtained if the immuno-supressive agent is used 15 days after the vaocine. The flagellates isolated from the vaccinateã Vbl treated mice remaineã avirulent for baby mice, after i.p. inoculation. The im m unity induceã by the PF strain is probably sterile i. e. does not imply in the persistence of a latent infection (premunition)