INDUCTION OF ANTICARBOHYDRATE ANTIBODIES BY PHAGE LIBRARY-SELECTED PEPTIDE MIMICS

One of the prerequisites for the development of polysaccharide subunit vaccines is the induction of an efficient immune response to carbohyd rate antigens like lipopolysaccharide (LPS) or capsular polysaccharide antigens of pathogens. In an attempt to overcome the problems that ar ise from the T-independent immune response induced by such antigens, s electing peptide sequences that mimic protective carbohydrate epitopes has been proposed. In this study, we investigate a new selection stra tegy for immunogenic peptide mimics using the phage-displayed peptide library technology. Two monoclonal antibodies (mAb) of the A isotype ( mIgA), mIgA C5 and mIgA I3, specific for the O-antigen (O-Ag) part of the human pathogen Shigella flexneri serotype 5a LPS and protective ag ainst homologous infection were used to screen two phage-displayed non apeptide libraries in pVIII. Using mIgA C5, 13 different specific clon es were selected, and 6 using mIgA 13; 5 of the latter also interacted in enzyme-linked immunosorbent assay with the first mAb. All of the 1 9 clones selected were separately used to immunize mice, but only 2 of them, p100c (mIgA I3-specific) and p115 (interacting with both mIgA) were able to induce anti-O-Ag antibodies. The immune response was spec ific for the O-Ag of the S, flexneri serotype 5a, and also selectively recognized the corresponding bacterial strain, The amino acid sequenc es of p100c and p115 immunogenic peptide mimics were YKPL-GALTH (flank ed by two Cys residues) and KVPPWARTA, respectively. These results are the first example of immunogenic mimicry of carbohydrates by phage-di splayed peptides, and indicate a new strategy of selection of immunoge ns for the development of anti-polysaccharide vaccines.