Humoral immune response kinetics in Philander opossum and Didelphis marsupialis infected and immunized by Trypanosoma cruzi employing an immunofluorescence antibody test

Philander opossum and Didelphis marsupialis considered the most ancient mam mals and an evolutionary success, maintain parasitism by Trypanosoma cruzi without developing any apparent disease or important tissue lesion. In orde r to elucidate this well-balanced interaction, we decided to compare the hu moral immune response kinetics of the two didelphids naturally and experime ntally infected with T. cruzi and immunized by different schedules of paras ite antigens, employing an indirect fluorescence antibody test (IFAT). Both didelphids responded with high serological titers to different immunizatio n routes, while the earliest response occurred with the intradermic route. Serological titers of naturally infected P. opossum showed a significant in dividual variation, while those of D. marsupialis remained stable during th e entire follow-up period. The serological titers of the experimentally inf ected animals varied according to the inoculated strain. Our data suggest t hat (1) IFAT was sensitive for follow-up of P. opossum in natural and exper imental T. cruzi infections; (2) both P. opossum and D. marsupialis are abl e to mount an efficient humoral immune response as compared to placental ma mmals, (3) experimentally infected P. opossum and D. marsupialis present di stinct patterns of infection depending on the subpopulation of T. cruzi, (4 ) the differences observed in the humoral immune responses between P. oposs um and D. marsupialis, probably, reflect distinct strategies selected by th ese animals during their coevolution with T. cruzi.