The influence of orientation and number of copies of T and B cell epitopes on the specificity and affinity of antibodies induced by chimeric peptides.

CBA and TO mice were immunized with chimeric peptide immunogens consisting of B cell (residues 404-414) and T cell (residues 288-302) epitopes from the F protein of measles virus. The chimeras were co-linearly synthesized to contain one or two copies of the T cell epitope linked to one or two copies of the B cell epitope via a glycine.glycine spacer. Two orientations were synthesized such that the T cell epitope(s) were located at either the amino or carboxyl terminus of the B cell epitope(s). The levels of antibody induced following immunization with the chimeras were assessed by enzyme-linked immunosorbent assay using microtiter plates coated with either the homologous chimera or the B cell epitope sequence. The affinities of the anti-chimera antibodies for the B cell epitope were assessed by a fluid-phase double-isotope radioimmunoassay. All the chimeras induced good antibody responses in both strains of mice with specificity for the B cell epitope. Chimeras containing two copies of the T cell epitope induced antibodies with higher affinity for the B cell epitope than did chimeras containing one copy of the T cell epitope or two copies of the B cell epitope. Furthermore, the amino terminal location of the T cell epitope in relation to the B cell epitope in the chimera induced higher affinity anti-B cell antibody than did the reverse orientation. These results suggest that orientation of epitopes and amino acid composition of chimeric peptides affect antigen processing and presentation to T cells which govern both the specificity and affinity of antibody produced. Thus, for the production of synthetic peptide immunogens with vaccine potential, attention needs to be given to the number and orientation of the component epitopes required to produce highest affinity antibody.