Acquired immunity in mice infected with strains of immunological types A and B of Trypanosoma cruzi

Abstract

Groups of 20 mice were inoculated with cultural forms of strains of Trypanosoma cruzi of two distinct immunological types: strains Y and L isolated from humans; M, from a bat (type A); strains 8857 and OPF, from opossums; and 8717, from a wild rat (type B). Parasitemia and mortality rates recorded during 7 weeks showed the human strains to be more infective than the animal strains, the course of parasitemia being, however, quite different when human strains Y and L were compared. A challenge inoculation of blood forms of virulent Y strain was performed in half of the mice previously inoculated with the cultural forms of each strain, the other half being kept as controls. Subsequent observation for 8 weeks revealed that some protection was conferred by all strains, but while no definite differences in mortality rates were verified, the proportion of animals with parasitemia was lower among mice previously infected with cultural forms of the Y (homologous) strain. Protection tests could not distinguish type A and B strains of T. cruzi; this suggests that defense mechanisms do not depend on the antigenic differences responsible for the “ in vitro” typing of the strains.