Characterization of autoantibodies generated in mice by immunization with the C-terminal region of Trypanosoma cruzi ribosomal P1 and P2 proteins

The R13 peptide sequence (EEEDDDMGFGLFD) that corresponds to the C-terminal region of Trypanosoma cruzi ribosomal P1 and P2 proteins differs from the eukariotic P consensus sequence EESDDDMGFGLFD (H13) only in a nonconservati ve amino acid substitution. Since the immunization with R13 peptide coupled to a carrier protein like OVA would break the tolerance to a self-sequence and generate autoantibodies, we characterized the antibodies induced in mi ce by R13 immunization, analyzing by ELISA their capacity to bind to R13 an d the self-sequence H13. Besides, we studied the course of these reactiviti es a long time after immunization. It was found that all R13-immunized mice had antibodies against H13 and this reactivity was always lower than R13 r eactivity. The anti-H13 reactivity evaluated by competitive ELISA demonstra ted that the H13 peptide is able to inhibit the binding of immune sera to R 13 at high doses. When the levels and the avidity of anti-R13 and anti-H13 were evaluated at 10 and 80 days post third immunization, it was observed t hat anti-R13 levels were higher than anti-H13 levels in all sera from 10 da ys after the third immunization. However, avidity of both antibodies was hi gh. In sera from 80 days post third immunization, anti-R13 and anti-H13 lev els and avidity either remained elevated or showed a rise, whereas anti-OVA levels declined. Moreover, when ECG traces were obtained from immunized mi ce, the heart functional alterations observed at 10 days continued at 80 da ys after the third immunization, showing an association with the levels of the antibodies. In addition, the isotype pattern that recognizes R13 and th e self-sequence H13 is different. For anti-R13 response, IgG1 reactivity wa s higher than IgG2; meanwhile, for anti-H13 response IgG2 reactivity was hi gher than IgG1. These results indicate that sera from R13-immunized mice bi nd the H13 sequence and this autoreactivity may be self-perpetuating. (C) 1 999 Academic Press.