Trypanosoma cruzi exoantigens: can those recognized by sera from chagasic patients trigger a protective immune response in mice?

Exoantigens (Ea) of Trypanosoma cruzi released in blood during the acute phase of experimental murine infection and recognized as antigens by sera from chagasic patients were grouped into two zones: one zone of pl 4–5 (Ea4–5), which had components of 35 kDa, 50 kDa and slightly higher than 100 kDa, MW, and another zone, of pl 6–7 (Ea6–7), with Ea of 50 kDa, 66-80 kDa and higher than 100 kDa. Immunization of mice with Ea4-5 or Ea6-7 prior to infection induced a protective immune response, as judged by levels of parasitaemia which were significantly lower than those of controls. Analysis of the immune response by skin test revealed that both groups of Ea induced immediate type hypersensitivity, the values of which were higher in animals immunized with Ea4-5. These antigens also induced specific cellular immunity (delayed-type hypersensitivity). There was a direct correlation between intensity of reactivity and the drop in the number of blood forms of parasites in these animals. Antibodies able to fix to the epimastigote surface were also detected by ELISA and the immunofluorescence test in mice immunized with Ea4-5 or Ea6-7. There were no qualitative or quantitative differences in the antibody induced by the two groups of Ea; the main isotypes of these antibodies which recognized Ea expressed on the parasite surface were IgG1 and IgG2. Les exoantigènes (Ea) de Trypanosoma cruzi relargués dans le sang au cours de la phase aiguë de l'infection expérimentale de la souris, ct reconnus comme antigènes par le sérum de patients atteints de la maladie de Chagas, se groupent dans deux zones en isoélectrofocalisation: les Ea4-5 (pI 4–5) dont les composants ont un poids moléculaire de 35, 50 et légèrement supériur à 100 kDa, et les Ea6-7 (pI 6–7) qui ont un poids moléculaire de 50, 66–80 et > 100 kDa. L'immunisation des souris par les Ea4–5 ou 6–7 préalablement à l'infection expérimentale, induit une réponse immunitaire protectrice, évaluée par les niveaux de parasitémie, significativement plus basse que celle des témoins. L'analyse de la réponse immunitaire par test cutané révèle que les 2 groupes d'Ea induisent une hypersensibilité de type immédiat dont l'intensité est plus élevée chez les animaux immunisés par les Ea4–5. Ces antigènes induisent aussi une immunité cellulaire spécifique (hypersensibilité de type retardé). Il y a correlation directe entre l'intensité de ces réactions et la baisse du nombre de parasites sanguins chez ces animaux. Des anticorps capables