title: Retro-inverso peptide analogues of Trypanosoma cruzi B13 protein epitopes fail to be recognized by human sera and peripheral blood mononuclear cells.
abstract: Retro inverso (RI) analogues of antigenic synthetic peptides, which are made of D-amino acids with a reversed sequence, may mimic the side chain conformation of natural all-L peptides. RI analogues were cross-reactively recognized by antibodies and CD4+ T cells reactive against natural all-L synthetic peptides or native proteins in animal models. Since peptides containing D-amino acids are highly resistant to proteolytic digestion, cross-reactive RI analogues may be ideal for in vivo administration to humans as synthetic peptide vaccines or immunomodulators. B13 is an immunodominant tandemly repetitive protein from Trypanosoma cruzi, a protozoan parasite that is the causative antigen of Chagas' disease. In order to test whether RI peptides can be recognized by human antibody and T cells, we synthesized two all-L peptides containing the immunodominant B (S12) and T (S15.7) cell epitopes of B13 protein from T. cruzi and their retro (R, made of all-L amino acids with reversed sequence), inverso (I, made of all-D amino acids) and RI analogues. Recognition of peptides S12, S12-R, S12-I and S12-RI by anti-B13 antibodies in sera from T. cruzi-infected patients was tested in competitive ELISA assay with recombinant B13 protein as the solid phase antigen. Peptides S15.7 and its topological analogues were tested at the 10-50 microM range in proliferation assays on peripheral blood mononuclear cells (PBMC) from S15.7-responder individuals. The median percentage inhibition of B13 ELISA for peptide S12 was 94%, while those of the RI analogue or the other topological analogues were below 12%. While peptide S15.7 was recognized by PBMC from all subjects tested, none recognized the RI analogue of the S15.7 T cell epitope. Our results indicate that cross-reactivity with natural epitopes is not an universal property of RI analogues. This may limit the general applicability of the use of cross-reactive RI analogues as human vaccines and immunotherapeutic agents.
authors.affiliation: Laboratory of Immunology, Heart Institute (InCor), and Division of Allergy and Immunopathology, Department of Medicine, University of São Paulo School of Medicine, São Paulo, Brazil.
authors.forename: L K
authors.initials: LK
authors.lastname: Iwai
authors.forename: M A
authors.initials: MA
authors.lastname: Duranti
authors.forename: L C
authors.initials: LC
authors.lastname: Abel
authors.forename: M A
authors.initials: MA
authors.lastname: Juliano
authors.forename: J
authors.initials: J
authors.lastname: Kalil
authors.forename: L
authors.initials: L
authors.lastname: Juliano
authors.forename: E
authors.initials: E
authors.lastname: Cunha-Neto
mesh_terms: D000818:Animals; D001483:Base Sequence; D002455:Cell Division; D004797:Enzyme-Linked Immunosorbent Assay; D000939:Epitopes; D006680:HLA Antigens / Q000096:biosynthesis; D015235:HLA-B Antigens / Q000737:chemistry*; D059908:HLA-B13 Antigen; D006801:Humans; D007963:Leukocytes, Mononuclear / Q000378:metabolism*; D008969:Molecular Sequence Data; D010452:Peptide Biosynthesis; D010455:Peptides / Q000737:chemistry; D011485:Protein Binding; D013601:T-Lymphocytes / Q000166:cytology / Q000378:metabolism; D014349:Trypanosoma cruzi / Q000737:chemistry*
chemical_list: D000939:Epitopes; D006680:HLA Antigens; D015235:HLA-B Antigens; D059908:HLA-B13 Antigen; D010455:Peptides